Category Archives: PXW-FS7

A7, cameras, cinematography, PMW-F55, PXW, PXW-FS5, PXW-FS7, Shooting Tips, Technology

The great S-Log2 or S-Log3 debate.

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I’ve written about this many times before, but still it comes up again and again. Which is better? Which should I use? I hear all kinds of crazy comments and a lot of incorrect information, so first of all lets dispel a few myths:

S-Log2 captures more dynamic range than S-Log3, it goes to a higher level on the waveform, S-Log3 clips the highlights sooner.

On most of Sony’s current cameras S-Log2 and S-Log3 both currently record exactly the same dynamic range as this is limited by the sensors that Sony are using. The S-log3 curve could be used in a future camera to capture up to 16 stops and in fact the new Venice camera records over 15 stops.  But as all of Sony’s other cameras sensors can only see 14 stops and the S-Log3 curve is designed to go beyond 14 stops, stop No. 14 is not recorded all the way at the top of the recording range.  S-Log2 is a 14 stop maximum curve, so the peak level is recorded right at the top of the recording range. There is no space held in reserve for anything beyond 14 stops.

In Sonys current camera range (other than Venice) the limit is 14 stops whether it’s S-Log2 or S-Log3. The chart that Sony provide showing both S-Log2 and S-Log3 is a little confusing as it shows the entire gamma curve rather than what the camera can actually “see”. In their current implementations both curves stop at +6 stops over middle grey, both capture the same dynamic range, there is no difference.

S-Log2 is brighter than S-Log3 so it must be capturing highlights better.

No, not really, see above. Playback and on screen brightness comes from the levels chosen to record something at and is dependant on the shape and range of the gamma curve. But the actual captured range is dependant on what the sensor can cope with. As we are not changing the sensor, the captured dynamic range, brightness range and shadow range does not change between S-Log2 and S-log3, both of which take the entire sensor range (they just store that same range using slightly different levels or code values). After applying a LUT or other conversion to your normal viewing gamma both S-Log2 and S-log3 will have the same brightness, same highlight and same shadow range.

S-Log3 has noisy shadows.

No, not really. Shadows appear noisy with S-Log3 as the shadow part of the curve is stored using higher code values compared to S-Log2. So when you view S-Log3 uncorrected the shadows are raised and stretched on your conventional monitor and this gives the impression of a noisy picture. In reality once you restore the levels to normal there is no additional noise. See this article for a full explanation.

S-log-levels The great S-Log2 or S-Log3 debate.
Chart showing S-Log2 and S-Log3 plotted against f-stops and code values. Note how little data there is for each of the darker stops, the best data is above middle grey. Note that current sensors only go to +6 stops over middle grey so S-Log2 and S-Log record to different peak levels.

S-Log3 is newer than S-Log2 so it must be better.

Newer, perhaps not. Better, no not really. S-Log3 is based on the industry standard Cineon log gamma curve. This curve was developed in the 1980’s to allow the digitising of film using 10 bit data. So S-Log3 matches a curve designed to work with negative film and is capable of storing more than the 14 stops that most of the current cameras sensors can see. In effect it is an old log gamma curve. As it is a curve designed for more than 14 stops, when used in a 14 stop camera some of the available recording data is empty and wasted.

S-Log2 was specifically designed by Sony to work with an electronic sensor with 14 stops of dynamic range and is optimised to match the performance characteristics of video sensors. By using a 14 stop curve with a 14 stop camera almost every bit of available data is utilised, there is no wastage. So S-Log2 makes better use of the data you have available to you,

BUT THERE ARE SOME OTHER FACTORS WE NEED TO CONSIDER.

S-Log2 and S-Gamut:

As well as the gamma curve we also have different Gamuts or color ranges. S-Log2 was originally designed for the F65 camera. The F65 sensor can capture a huge color range beyond the range that most conventional video sensors can see. So as well as S-Log2 Sony introduced S-Gamut which was matched to the very wide color range of the F65 sensor. S-Log2 is designed to be used with S-Gamut. But many of the cameras we use, like the FS7, F5, FS5 cannot see this color range (Sony’s F55 and Venice can). In addition this very large color range can be a little tricky to deal with in post production. Add to this the fact that S-Log2 is quite different to the quite common Cineon gamma curve and behaves differently to other curves in post. The end result was that in the early days of S-Log2 there were a number of complaints and comments that Sony’s S-log2 material was difficult to grade.

S-Log3 and S-Gamut3.

Because some people were struggling a bit with S-Gamut and S-Log2 in post production (Resolve and many of the other tools we have today were not as well developed 4 years ago), Sony introduced S-Gamut3 and S-log3 as well as a further Gamut called S–Gamut3.cine. S-Log3 was based on Cineon as that’s what people were familiar with. Arri’s Log-C is also based on Cineon as are many other log curves. This makes it a more “familiar” grading experience for many colorists. In addition Sony created a modified version of the super large S-Gamut to make it easier to grade.  S-Gamut3 is just as big as S-Gamut but some tweaks inside make it easier to grade (fewer color shifts). At the same time Sony realised that most users were producing content for TV, the web or digital cinema that had little use for the huge color range of S-Gamut/S-Gamut3.  So S-Gamut3.cine was developed as a smaller, more manageable version of S-Gamut3 and it incorporated a few tweaks to the color science to provide colors closer to those used by other manufacturers. S-Gamut3.cine is also a better match for cameras with sensors that cannot see the full S-Gamut range (like the FS5, FS7, F5, A7).

The end result is that in general most people prefer or find it easier to grade S-Log3/S-Gamut3.cine material than S-Log2/S-Gamut. Plus you can often use LUT’s designed for Log-C or Cineon with S-log3 material (this isn’t optimum, but it can work).

Gamuts-1024x632 The great S-Log2 or S-Log3 debate.
SGamuts Compared.

Getting the data from camera to post.

In terms of getting the data from your cameras sensor in to post production S-Log2 is the better choice (unless you have a Sony Venice which only has S-Log3). S-Log2 is optimised for the way an electronic sensor works. S-log3 is essentially a curve designed for negative film applications, not video and no matter how you look at it, these are electronic video cameras. However, if you are recording 10 bit or greater you have a lot of data whichever curve you use, so in practice it will be rare to see any difference in the final result.

So use the curve you find easiest to work with. It is true that S-Log 3 allocates a little more data to the shadows and less to the highlights than S-Log2, but don’t confuse data and code values with more range. S-Log3 has a few extra code values in it’s darkest stops, S-log2 has a few extra in the bright stops, but the dynamic range, highlight and shadow handling is governed by the sensor not the gamma curve. Overall S-Log3 has fewer code values than S-Log2, S-Log2  makes better use of the data available, but with 10 bit this really isn’t going to make a huge difference.

8 Bit Recording.

But if you are only recording with an 8 bit codec you are already at a disadvantage. When recording 8 bit you really need to maximise the way what little data you have is used. For that reason I will always recommend that S-Log2 is used when recording 8 bit on a camera like the FS5 in UHD or A7s or similar (FS5 is 10 bit in HD). By using S-Log2 you are using as many of the limited code values available as you can. This doesn’t mean you can’t use S-log3, it just wouldn’t be my choice.

The end result should be the same.

At the end of the day, if you were to use matching LUTs, S-log2 and S-log3 material should look more or less exactly the same after grading or application of the LUT, no matter what the scene you are shooting. If they do look significantly different then you are doing something wrong. So your choice of curve, other than for 8 bit recordings will most likely come down to ease of use rather than anything else.

If your camera doesn’t have LUT’s then S-Log2 can be easier to work with as it is more contrasty. This makes it a bit easier to focus and also makes it easier to gauge exposure. If your camera has LUT’s and you use them, then you may decide to use S-Log3 simply because you should find it a little easier to work with in post. Either way both curves capture the same range of picture information and both should give more or less the same end result.

There may be some very, very subtle differences due to the small differences in data distribution, but often these will be hard to really see in the final image.

cameras, PMW-F55, PXW-FS5, PXW-FS7, Scene Files and Luts

Looking For LUT’s for the Sony S-Log2 and S-Log3 Cameras?

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This website has a great feature. If you look up in the top left corner of every page you will see a small magnifying glass symbol. If you click on that it will allow you to search the entire site for information… and there’s lots and lots of hint, tips and guides going back many years.

One thing though that a lot of people keep asking about is LUT’s or Look Up Tables. I have lots and they are all (for the moment at least) provided for free. There will be some paid LUT sets coming soon. If you follow the link below you will get a single page that lists all the current LUT articles on the web site. Links to my free LUT sets will be included in these articles.

Remember that LUT’s for S-Log2 and S-Log3 can be used in any camera with S-Log2 or S-Log3. So a LUT for the FS7 can also be used in the FS5 for example.

Here’s the link: https://www.xdcam-user.com/?s=LUT%27s

cameras, HDR, PXW-FS7, Technology

What does Rec-2020 on the PXW-FS7 II really mean?

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So, as you should have seen from my earlier post Sony has included Rec-2020 as a colorspace in custom mode on the new FS7 II. But what does this mean and how important is it? When would you use it and why?

Recommendation ITU BT.2020 is a set of standards created by the International Telecommunications Union for the latest and next generation of televisions. Within the standard there are many sub-standards that define things such as bit depth, frame size, frame rates, contrast, dynamic range and color.

Sony-Colorspaces-1024x815 What does Rec-2020 on the PXW-FS7 II really mean?
The colorspaces that Sony’s cameras can capture.

The Rec-2020 addition in the the FS7 II specifically refers to the color space that is recorded, determining the range of colors that can be recorded and the code values used to represent specific tones/hues.

First of all though it is important to remember that the FS7 II shares the same sensor as the original FS7, the FS5 and F5. Sony has always stated that this sensor is essentially a “709” sensor. The sensor in Sony’s PMW-F55 can capture a much greater color range (gamut) than the F5, FS5 and FS7, only the F55 can actually capture the full Rec-2020 color space, the FS7 II sensor cannot. It’s very difficult to measure the full color gamut of a sensor, but from the tests that I have done with the F5 and FS7 I estimate that this sensor can capture a color gamut close to that of the DCI-P3 standard, so larger than Rec-709 but not nearly as large as Rec-2020 (I’d love someone to provide the actual color gamut of this sensor).

So given that the FS7 II’s sensor can’t actually see colors all that far beyond Rec-709 what is the point of adding Rec-2020 recording gamut as the camera can’t actually fill the recording Gamut? Similarly the F5/FS5/FS7 cannot fill S-Gamut or S-Gamut3.

The answer is – To record the colors that are captured with the correct values. If you capture using Rec-709 and then play back the Rec-709 footage on a Rec-2020 monitor the colors will look wrong. The picture will be over saturated and the hues slightly off. In order for the picture to look right on a Rec-2020 monitor you need to record the colors at the right values. By adding Rec-2020 to the FS7 II Sony have given users the ability to shoot Rec-2020 and then play back that content on a Rec-2020 display and have it look right. You are not capturing anything extra (well, maybe a tiny bit extra), just capturing it at the right levels so it at least looks correct.

As well as color, Rec-2020 defines the transfer functions, or gamma curves to you and me, that should be used. The basic transfer function is the same as used for Rec-709, so you can use Rec-709 gamma with Rec-2020 color to get a valid Rec-2020 signal. For full compatibility this should be 3840×2160 progressive and 10bit (the Rec-2020 standard is a minimum of 10bit and as well as 3840×2160 also includes 7680×4320).

But, one of the hot topics right now in the high quality video world is the ability to display images with a much greater dynamic range than the basic Rec-709 or Rec-2020 standards allow. There is in fact a new standard called Rec-2100 specifically for HDR television. Rec-2100 uses the same colorspace as Rec-2020 but then pairs that bigger colorspace with either Hybrid Log Gamma or ST2084 gamma, also know as PQ (Perceptual Quantiser). As the FS7 II does not have PQ or HLG as gamma curves you cannot shoot material that is directly compatible with Rec-2100. But what you can do is shoot using S-Log2/S-Log3 with S-Gamut/S-Gamut3/SGamut3.cine which will give you the sensors full colorspace with the sensors full 14 stop dynamic range. Then in post production you can grade this to produce material that is compatible with the Rec-2100 standard or the Rec-2020 standard. But of course you can do this with an original FS7 (or F5) too.

So, when would you actually  use the FS7 II’s Rec-2020 colorspace rather than S-Log/S-Gamut?

First of all you don’t want to use it unless you are producing content to be shown on Rec-2020 displays. Recording using Rec-2020 color gamut and then showing the footage on a Rec-709 display will result in washed out colors that don’t look right.

You would probably only ever use it if you were going to output directly from the camera to a monitor that only supports Rec-2020 color or for a project that will be specifically shown on a standard dynamic range Rec-2020 display. So, IMHO this extra colorspace is of very limited benefit. For most productions regular Rec-709 or S-Log/S-Gamut will still be the way forward unless Sony add Hybrid Log Gamma or PQ gamma to the camera as well. Adding HLG or PQ however has problems of it’s own as the existing viewfinders can only show standard dynamic range images, so an external HDR capable monitor would be needed.

Rec-2020 recording gamut is a nice thing to have and for some users it may be important. But overall it’s not going to be a deal breaker if you only have a standard FS7 as the S-Log workflow will allow you to produce Rec-2020 compatible material.

 

 

cameras, PXW-FS7, Review

PXW-FS7 II. New camera that does NOT replace the FS7.

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2_SideL-1024x754 PXW-FS7 II. New camera that does NOT replace the FS7.
The new Sony PXW-FS7MKII. Can you spot the differences?

By the time you get to read this you may already know almost everything there is to know about the PXW-FS7 II as it has been leaked and rumoured all over the internet. But I’m under a Sony NDA, so have had to keep quiet until now.

And I’ve been told off for calling it a MKII,  the correct name is PXW-FS7 II. Sorry Mr Sony, but if you call it FS7 II, most people will think the “II” means MKII.

The FS7 camera is a mature product. By that I mean that  the early bugs have been resolved. The camera has proven itself to by reliable, cost effective (amazing bang for the buck really). To produce great images and 4K files that are not too big.  It can do slow-mo, 4K, 2K, HD and raw via an adapter and external recorder. As a result the FS7 is now one of the top choices for many broadcasters and production companies. It has become an industry standard.

The first and most important thing to understand about the FS7 II is that it does not replace the existing FS7. I would have preferred it if Sony had called this new camera the “FS7 Plus”. The “II” designation (which I take to mean MKII) implies a replacement model, replacing the MKI. This is not the case. The FS7 II is in fact a slightly upgraded version of the standard FS7 with a few hardware improvements. The upgrades make the MKII quite a lot more expensive (approx 10K Euros), but don’t worry. If you don’t need them, you can stick with the cheaper FS7 MK1 which remains a current model. In terms of image quality there is no real difference, the sensor and image processing in the cameras is the same.

So what are the changes?

20161102_153512-1024x576 PXW-FS7 II. New camera that does NOT replace the FS7.
A square rod supports the viewfinder on the PXW-FS7MKII

The most obvious perhaps is the use of a square rod to support the viewfinder. This eliminates the all too common FS7 problem of sagging viewfinders. As well as switching to a square rod each of the adjustments for the viewfinder mounting system now has a dedicated clamp. Before if you wanted to slide the viewfinder forwards or backwards you undid a clamp that not only freed off the sliding motion but also controlled the tilt of the screen. So it was impossible to have the fore-aft adjustment slack for quick adjustments without the viewfinder sagging and drooping.

25-300x225 PXW-FS7 II. New camera that does NOT replace the FS7.
Another view of the revised viewfinder mounting system on the PXW-FS7 MKII

With the MkII you can have a slack fore-aft adjuster without the VF drooping. Overall the changes to the VF mounting system are extremely welcome. The VF mount on the Mk1 is a bit of a disaster, but there are plenty of 3rd party solutions to this. So you can fix the problems on a MKI without having to replace the camera. In addition, if you really wanted you could buy the FS7 II parts as spare parts and fit them to a MKI.

The Lens Mount.

19-966x1024 PXW-FS7 II. New camera that does NOT replace the FS7.
The new locking E-Mount on the PXW-FS7 MKII

The next obvious change is to the lens mount. The FS7 MK1 has a normal Sony E-Mount where you insert the lens and then twist it to lock it in to place. The FS7 II mount is still an E-Mount but now it has a locking collar like a PL or B4 mount. This means that you have to insert the lens at the correct angle and then you turn a locking ring to secure the lens. The lens does not rotate  and once locked in place cannot twist or turn and has no play or wobble. This is great for those that use a follow focus or heavier lenses. BUT the new locking system is fiddly and really needs 2 hands to operate. In practice you have to be really careful when you mount the lens. It’s vital that you align the white dot on the lens with the white dot on the mount before you twist the locking ring.

20161102_153624-1024x576 PXW-FS7 II. New camera that does NOT replace the FS7.
Make sure the dots are correctly aligned! PXW-FS7 II lens mount.

As you rotate the locking ring a small release catch drops into place to prevent the ring from coming undone. But if the lens isn’t correctly aligned when you insert it, the lens can rotate with the locking ring, the catch clicks into place, but the lens will just drop out of the mount. When inserted correctly this mount is great, but if you are not careful it is quite easy to think the lens is correctly attached when in fact it is not.

Variable ND Filter.

16-1024x813 PXW-FS7 II. New camera that does NOT replace the FS7.
The PXW-FS7MKII has a variable ND filter.

Behind the lens mount is perhaps the most significant upgrade. The FS7 II does away with the rotating filter wheel and replaces it with the variable ND filter system from the FS5. I have to say I absolutely love the variable ND on the FS5. It is so flexible and versatile. You still have a 4 position filter wheel knob. At the clear position the ND filter system is removed from the optical path. Select the 1, 2 or 3 positions and the electronically controlled ND filter is moved into position in front of the sensor. You then have 3 preset levels of ND (the level of which can be set in the camera menu) or the ability to smoothly control the level of ND from a dial on the side of the camera. Furthermore you can let the camera take care of the ND filter level automatically. The real beauty of the variable ND s that it allows you to adjust your exposure without having to alter the aperture (which changes the depth of field) or shutter (which alters the flicker/cadence). It’s also a great way to control exposure when using Canon lenses as the large aperture steps on the Canon lenses can be seen in the shot.

20161102_154454-1024x576 PXW-FS7 II. New camera that does NOT replace the FS7.
New arm on the PXW-FS7 II

Another physical change to the camera is the use of a new arm for the handgrip. The new arm has a simple wing-nut for length adjustment, much better than the two screws in the original arm. In addition you can now use the adjuster wing-nut to attach the arm to the camera body and this brings the hand grip very close to the body for hand held use. This is a simple but effective improvement, but again 3rd party handgrip arms are available for the base model FS7.

FS72-loupe-1024x784 PXW-FS7 II. New camera that does NOT replace the FS7.
Improved viewfinder loupe attachment on the FS7 MKII.

The viewfinder loupe has seen some attention too. The standard FS7 loupe has two fiddly wire clips that have to be done up to secure the loupe to the viewfinder. The MK2 loupe has a fixed hook that slips over the top lug on the viewfinder so that you now only need to do up a single catch on the bottom of the loupe. It is easier and much less fiddly to fit the new loupe, but the optics and overall form and function of the loupe remain unchanged.

20161102_154540-1024x576 PXW-FS7 II. New camera that does NOT replace the FS7.
Folding sunshade on the PXW-FS7 MKII

As well as the loupe the FS7 II will be supplied with a clip on collapsable sunshade for the viewfinder. This is a welcome addition and hand held shooters will no doubt find it useful. When not in use the sunshade folds down flat and covers the LCD screen to protect it from damage.

The number of assignable buttons on the FS7 II is increased to 10. There are 4 new assignable button on the camera body where the iris controls are on the original FS7.  The Iris controls are now on the side of the camera just below the ND filter wheel along with the other ND filter controls. These buttons are textured to make them easier to find by touch and are a very welcome addition, provided you can remember which functions you have allocated to them. It’s still a long way from the wonderful side panel LCD of the PMW-F5/PMW-F55 with it’s 6 hotkeys and informative display of how the camera is configured.

20161102_154716-1024x576 PXW-FS7 II. New camera that does NOT replace the FS7.
Power indicator light just above the power switch on the PXW-FS7 MKII

Tucked under the side of the camera and just above the power switch there is now a small green power LED. The original FS7 has no power light so it can be hard to tell if it’s turned on or not. This little green light will let you know.

The last hardware change is to the card slots. The XQD card slots have been modified to make it easier to get hold of the cards when removing them. It’s a small change, but again most welcome as it can be quite fiddly to get the cards of an FS7.

REC-2020.

A further change with the FS7 II is the addition of Rec-2020 colorspace in custom mode. So now with the FS7 II as well as Rec-709 colorspace you can also shoot in Rec-2020. I’m really not sure how important this really is. If Sony were to also add Hybrid Log Gamma or PQ gamma for HDR then this would be quite useful. But standard gammas + Rec2020 color doesn’t really make a huge amount of sense. If you really want to capture a big range you will probably shoot S-Log2/3 and S-Gamut/S-Gamut3.

So – the big question – is it worth the extra?

Frankly, I don’t think so. Yes, the upgrades are nice, especially the variable ND filter and for some people it might be worth it just for that. But most of the other hardware changes can be achieved via 3rd party accessories for less than the price difference between the cameras.

With all the financial turmoil going on in many countries right now I think we can expect to see the cost of most cameras start to rise, including the original (but still current) FS7. This may narrow the price gap between the FS7 MKI and FS7 MK2 a little. But an extra 3000 Euros seems a high price to pay for a variable ND filter.

In some respects this is good news as it does mean that those that have already invested in an FS7 MKI won’t see that investment diminished, the MK1 is to remain a current model alongside the souped up MK2 version. Now you have a choice, the lower cost workhorse FS7 MK1 or the MK2 with it’s variable ND filter and revised lens mount.

cameras, PXW-FS5, PXW-FS7

Training Videos for the PXW-FS5 and PXW-FS7

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Just a reminder that the full sets of traing films for the PXW-FS5 and the PXW-FS7 are available for viewing for free on YouTube.

The FS7 videos can be found by following this playlist link.

There are 10 videos taking you from basic setup all the way through scene files, cine EI and the effects shooting modes.

There are currently 2 PXW-FS5 videos.

The first on picture profiles and picture settings is here.

The second on the advanced shooting modes is here.

I am currently working on a further video on using the FS5’s raw output and this should be available in the next couple of weeks.

Don’t forget if you have any questions I have my Webinar day coming next week.

 

Free Webinar Day – July 26th 2016.

cameras, PMW-F55, PXW-FS7, Technology

Revealing Signal to Noise and Exposure experiment for PMW-F5, F55 and FS7.

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Here’s a little experiment for you to try if you have a PMW-F5, PMW-F55 or PMW-FS7. It should help you understand a few key things about the way these cameras behave, notably:

1: Why ISO does not actually reflect the sensitivity of the camera.

2: Why it is beneficial to expose S-Log2 or S-Log3 brighter than the Sony recommended levels.

3: How to get the best possible S-Log footage.

4: Why S-log may be a poor choice for low light.

Ideally you will want to use an external waveform monitor connected to the cameras SDI output, but it is possible to use the built in waveform display.

Start with the camera in Custom mode. Choose “STD” gamma and Rec-709. Set the gain/ISO settings so that the camera is showing ISO.

Set the ISO to the base ISO (800 ISO on F5/FS7, 500 ISO on F55).

Expose a 90% white card so that white is 90% on the waveform display. This doesn’t need to be 100% accurate, you can use a piece of paper if you don’t have a proper white card. Don’t change the ISO/Gain, light the white card if you need to. Make a note of the aperture.

Now change the gamma selection to S-Log2, do not change the exposure.

Note how white now drops down to about 70% and also note that the ISO becomes 2000 ISO on an F5 or FS7 and 1250 ISO on an F55.

Think about this for a moment: If the ISO has gone up, how can white and the bulk of my image become darker?

Now switch the camera to show dB gain instead of ISO, the gain should be showing 0dB. Repeat the above switching from Standard 709 gamma to S-Log2 and note that the gain remains at 0dB for both rec-709 and S-Log2.

Think about this: The gain is the same for both 709 and S-log2 but the S-Log2 image is darker. As the gain is NOT changing then the sensitivity is not actually changing, so why does the ISO change?

If you were to use a light meter and start off with the light meter set to 800 (500) ISO the light meter would tell you to set the aperture to whatever it is you currently have to give the correct exposure in rec-709 with white at 90%.  If you had a light meter and you change the ISO setting on the light meter from 800(500)ISO to 2000(1250) ISO the light meter will tell you to close the aperture by 1.3 stops.

So, on your camera, while it is set to S-Log2 close the aperture from it’s original setting by 1.3 stops. Now you will find that white will be at the recording levels given by Sony for S-Log2 which is 59% for white and 32% for middle grey.

So what have we learnt from this? The gain is the same for both standard gamma and S-Log2, even though the ISO changes from 800(500) to 2000(1250) ISO. So the sensitivity and amount of noise coming from the sensor is the same in both cases. But the indicated ISO changes so that if you are using an external light meter, when you switch to S-Log the higher indicated ISO  will make the light meter tell you to close the aperture. This means there is less light falling on the sensor. This means that the recorded image will have a worse signal to noise ratio (noise remains the same, but signal is smaller).

To solution of course to this poorer signal to noise ratio is simply to open the aperture back up again by 1.3 stops. When shooting S-Log2 or S-Log3 using the CineEI mode I always recommend using 800EI on an F5 or FS7 or 640EI on an F55. This means your aperture becomes the same as it would be when shooting in vanilla Rec-709, the end result is the same, improved, signal to noise ratio. If you are not using CineEI or LUT’s, then expose white at 70%.

cameras, PXW-FS7

PXW-FS7 CineEI Guide Updated.

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I have just completed a long overdue update to my guide to CineEI and S-Log2/S-Log3 on the PXW-FS7. I have made some changes to reflect the new expanded zebra range available in the latest firmware versions as well as the new waveform operation. I have also added in the two videos I have made on using CineEI. The first video covers setting up the Cine EI mode and how to expose S-Log2/3 and then the second video explains how to use the exposure index function to offset your exposure for less noise and grain.

https://www.xdcam-user.com/2014/12/ultimate-guide-for-cine-ei-on-the-sony-pxw-fs7/

cameras, PMW-F55, PXW-FS5, PXW-FS7, Shooting Tips, Technology, Workflow

Deeper Understanding Of Log Gamma. Experiments with a Waveform Display.

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I started writing this as an explanation of why I often choose not to use log for low light. But instead it’s ended up as an experiment you can try for yourself if you have a waveform monitor that will hopefully allow you to better understand the differences between log and standard gamma. Get a waveform display hooked up to your log camera and try this for yourself.

S-Log and other log gammas are wonderful things, but they are not the be-all and end-all of video gammas. They are designed for one specific purpose and that is to give cameras using conventional YCbCr or RGB recording methods the ability to record the greatest possible dynamic range with a limited amount of data, as a result there are some compromises made when using log. Unlike conventional gammas with a knee or gammas such as hypergammas and cinegammas, log gammas do not normally have any highlight roll off, but do have a shadow roll-off. Once you get above middle grey log gammas normally record every stop with almost exactly the same amount of data, right up to the clipping point where they hard clip. Below middle grey there is a roll off of data per stop as you go down towards the black clip point (as there is naturally less information in the shadows this is expected). So in many respects log gammas are almost the reverse of standard gammas. The highlight roll off that you may believe that you see with log is often just the natural way that real world highlights roll off anyway, after all there isn’t an infinite amount of light floating around (thank goodness). Or that apparent roll off is simply a display or LUT limitation.

An experiment for you to try.

xdcam-greyscale-300x169 Deeper Understanding Of Log Gamma. Experiments with a Waveform Display.
Click on the chart to go to larger versions that you can download. Display it full screen on your computer and use it as a test chart. You may need to de-focus the camera slightly to avoid aliasing from the screens pixels.

If you have a waveform display and a grey scale chart you can actually see this behaviour. If you don’t have a chart use the grey scale posted here full screen on your computer monitor. Start with a conventional gamma, preferably REC-709. Point the camera at the chart and gradually open up the aperture. With normal gammas as you open the aperture you will see the steps between each grey bar open up and the steps spread apart until you reach the knee point, typically at 90% (assuming the knee is ON which is the default for most cameras).  Once you hit the knee all those steps rapidly squash back together again.

What you are seeing on the waveform is conventional gamma behaviour where for each stop you go up in exposure you almost double the amount of data recorded, thus capturing the real world very accurately (although only within a limited range). Once you hit the knee everything is compressed together to increase the dynamic range using only a very small recording range, leaving the shadows and all important mid range well recorded. It’s this highlight compression that gives video the “video look”, washed out highlights with no contrast that look electronic.

If you repeat the same exercise with a hypergamma or cinegamma once again in the lower and mid range you will see the steps stretch apart on the waveform as you increase the exposure. But once you get to about 65-70% they stop stretching apart and now start to squeeze together. This is the highlight roll off of the hypergamma/cinegamma doing it’s thing. Once again compressing the highlights to get a greater dynamic range but doing this in a progressive gradual manner that tends to look much nicer than the hard knee. Even though this does look better than 709 + Knee in the vast majority of cases, we are still compressing the highlights, still throwing away a lot of data or highlight picture information that can never be recovered in post production no matter what you do.

Conventional video = Protect Your Highlights.

So in the conventional video world we are taught as cameramen to “protect the highlights”. Never overexpose because it looks bad and even grading won’t help a lot. If anything we will often err on the side of caution and expose a little low to avoid highlight issues. If you are using a Hypergamma or Cinegamma you really need to be careful with skin tones to keep them below that 65-70% beginning of the highlight roll off.

Now repeat the same experiment with Slog2 or S-log3. S-log2 is best for the experiment as it shows what is going on most clearly. Before you do it though mark middle grey on your waveform display with a piece of tape or similar. Middle grey for S-log2 is 32% (41% for S-log3).

Now open up the aperture and watch those steps between the grey scale bars. Below middle grey, as with the standard gammas you will see the gap between each bar open up. But take careful note of what happens above middle grey. Once you get above middle grey and all the way to the clip point the gap between each step remains the same.

So what’s happening now?

Well this is the S-log curve recording each stop above middle grey with the same amount of data. In addition there is NO highlight roll off. Even the very brightest step just below clipping will be same size as the one just above middle grey. In practice what this means is that it doesn’t make a great deal of difference where you expose for example skin tones, provided they are above middle grey and below clipping. After grading it will look more or less the same. In addition it means that that very brightest stop contains a lot of great, useable picture information. Compare that to Rec-709 or the Cinegammas/Hypergammas where the brightest  stops are all squashed together and contain almost no contrast or picture information.

Now add in to the equation what is going on in the shadows. Log has less data in the shadows than standard gammas because you are recording a greater overall dynamic range, so each stop is recorded with overall less data.

Standard Gammas = More shadow data per stop, much less highlight data = Need to protect highlights.

Log= Less shadow data per stop, much more highlight data = Need to protect shadows.

Hopefully now you can see that with S-log we need to flip the way we shoot from protecting highlights to protecting shadows. When you shoot with conventional gammas most people expose so the mid range is OK, then take a look at the highlights to make sure they are not too bright and largely ignore whats going on in the shadows. With Log you need to do the opposite. Expose the mid range and then check the shadows to make sure they are not too dark. You can ignore the highlights.

Yes, thats’ right, when shooting log: IGNORE the highlights!

WF-Cinegamma-3-1024x576 Deeper Understanding Of Log Gamma. Experiments with a Waveform Display.
Cinegamma highlight roll off. Note how the tree branches in the highlights look strangled and ugly due to the lack of highlight data, hence “protect your highlights”.
WF-Slog-graded-1024x576 Deeper Understanding Of Log Gamma. Experiments with a Waveform Display.
Graded S-Log2. Note how nice the same tree branches look because there is a lot of data in the highlights, but the shadows are a little crunchy. Hence: protect your shadows.

For a start you monitor or viewfinder isn’t going to be able to accurately reproduce the highlights as bright as they are . So typically they will look a lot more over exposed than they really are. In addition there is a ton of data in those highlights that you will be able to extract in the grade. But most importantly if you do underexpose your mid range will suffer, it will get noisy and your shadows will look terrible because there will be no data to work with.

When I shoot with log I always over expose by at least 1 stop above the manufacturer recommended levels. If you are using S-log2 or S-log3 that can be achieved by setting zebras to 70% and then checking that you are JUST starting to see zebras on something white in your shot such as a white shirt or piece of paper. If your camera has CineEI use an EI that is half of the cameras native ISO (I use 1000 or 800 EI for my FS7 or F5).

I hope these experiments with a grey scale and waveform help you understand what is going on with you gamma curves. One thing I will add is that while controlled over exposure is beneficial it can lead to some issues with grading. That’s because most LUT’s are designed for “correct” exposure so will typically look over exposed. Another issue is that if you simply reduce the gain level in post to compensate than the graded footage looks flat and washed out. This is because you are applying a linear correction to log footage. Fo a long tome I struggled to get pleasing results from over exposed log footage. The secret is to either use LUT’s that are offset to compensate for over exposure or to de-log the footage prior to grading using an S-Curve. I’ll cover both of these in a later article.

S-log-levels Deeper Understanding Of Log Gamma. Experiments with a Waveform Display.
Chart showing S-Log2 and S-Log3 plotted against f-stops and code values.

 

 

 

 

 

 

 

 

 

What about shooting in low light?

OK, now lets imagine we are shooting a dark or low light scene. It’s dark enough that even if we open the aperture all the way the brightest parts of the scene (ignoring things like street lights) do not reach clipping (92% with S-Log3 or 109% with S-Log2). This means two things. 1: The scene has a dynamic range less than 14 stops and 2: We are not utilising all of the recording data available to us. We are wasting data.

Log exposed so that the scene fills the entire curve puts around 100 code values (or luma shades) per stop above middle grey for S-log2 and 75 code values for S-Log3 with a 10 bit codec. If your codec is only 8 bit then that becomes 25 for S-log2 and 19 code values for S-Log3. And that’s ONLY if you are recording a signal that fills the full range from black clip to white clip.

3 stops below middle grey there is very little data, about thirty 10 bit code values for S-Log2 and about 45 for S-log3. Once again if the codec is 8 bit you have much less, about 7 for S-Log2 and about 11 for S-log2. As a result the darker parts of your recorded scene will be recorded with very little data and very few shades. This impacts how much you can grade the image in post as there is very little picture information in the darker parts of the shot and noise tends to look quite coarse as it is only recorded with a limited number of steps or levels (this is particularly true of 8 bit codecs and an area where 8 bit recordings can be problematic).

So what happens if we use a standard gamma curve?

Lets say we now shoot the same scene with a standard gamma curve, perhaps REC-709. One point to note with Sony cameras like the FS5, FS7, F5/F55 etc is that the standard gammas normally have a native ISO one to two stops lower than S-Log. That’s because the standard gammas ignore the darkest couple of stops that are recorded when in log. After all there is very little really useable picture information down there in all the noise.

Now our limited dynamic range scene will be filling much more of our recording range. So straight away we have more data per stop because we are utilising a bigger portion of the recording range. In addition because our recorded levels will be higher in our recording range there will be more data per stop, typically double the data especially in the darker parts of the recorded image. This means than any noise is recorded more accurately which results in smoother looking noise. It also means there is more data available for any post production manipulation.

But what about those dark scenes with problem highlights such as street lights?

This an area where Cinegammas or Hypergammas are very useful. The problem highlights like strret lights normally only make up a very small part of your your overall scene. So unless you are shooting for HDR display it’s a huge waste to use S-log just to bring some highlights into range as you make big compromises to the rest of the image and you’ll never be able to show them accurately in the finished image anyway as they will exceed the dynamic range of the TV display.  Instead for these situations a Hypergamma or Cinegamma works well because below about 70% exposure Hypergammas and cinegammas are very similar to Rec-709 so you will have lots of data in the shadows and mid range where you really need it. The highlights will be up in the highlight roll off area where the data levels or number of recorded shades are rolled off. So the highlights still get recorded, perhaps without clipping, but you are only giving away a small amount of data to do this. The highlights possibly won’t look quite as nice as if recorded with log, but they are typically only a small part of the scene and the rest of the scene especially the shadows and mid tones will end up looking much better as the noise will be smoother and there will be more data in that all important mid-range.

 

cameras, cinematography, PMW-F55, PXW-FS5, PXW-FS7, Shooting Tips

Treat it like a film camera!

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If you have a modern camera that can record log or raw and has 13 stops or more of dynamic range you need to stop thinking “video” and think “film”.

A big mistake most traditional video camera operators make with these big DR cameras is to treat them as they would a typical limited dynamic range video camera and constantly worry and obsess about protecting highlights. Why do we do this? Well probably because that’s what you do with cameras with a very limited range and that’s probably what you have had drummed into you for years. But now with modern large sensor cameras everything changes. When you get to a 14 stop range camera, even if you choose to shoot 2 stops over exposed  (perhaps by using 500 EI on an FS7 or F5) you still have as much or more over exposure range as a conventional video camera and the highlight range that you do have is not subject to a knee or other similar acute highlight compression. So any highlights will contain a ton of high quality, usable picture information. By shooting over exposed by a controlled amount (1 to 2 stops), perhaps by using a low EI you gain very big improvements in the signal to noise ratio and get better saturated colors (opening the aperture lets more light onto the sensor, your colors will be better recorded). This allows you to pull a lot more information out of the data thin shadows and mid range. Most cameras that use log have very little data in the shadows. If you are recording with a 10 bit codec cameras that use variations of the Cineon log curve (Arri LogC, Sony S-Log3, Panasonic V-Log) only have about 80 luma shades covering the first 4 stops of exposure in total. Above the 4th stop the amount of data per stop increases rapidly so a little bit of deliberate over exposure really helps lift your darkest shadows up out of the noise and mire. Up in the highlights each stop has exactly the same amount of data, so over exposing a bit doesn’t compress the highlights as it would with a conventional camera, so a bit of mild over exposure is normally not noticeable.

Really with a 14 stop log camera you want to treat it like film, not video. Just like film, a 14 stop log camera will almost always benefit from a controlled amount of over exposure, highlights will rarely suffer or look bad just because you’re one stop hot, but he shadows and midtones will be significantly improved. And just like film, if you under expose log you will take a big hit. You will loose a lot of shadow information very quickly, have less color, it will be noisy and the highlight benefit will be marginal.