Tag Archives: Luts

Using LUT’s for exposure – choosing the right LUT.

If using a LUT to judge the exposure of a camera shooting log or raw it’s really important that you fully understand how that LUT works.

When a LUT is created it will expect a specific input range and convert that input range to a very specific output range. If you change the input range then the output will range will be different and it may not be correct. As an example a LUT designed and created for use with S-Log2 should not be used with S-Log3 material as the the higher middle grey level used by S-Log3 would mean that the mid range of the LUT’s output would be much brighter than it should be.

Another consideration comes when you start offsetting your exposure levels, perhaps to achieve a brighter log exposure so that after grading the footage will have less noise.

Lets look at a version of Sony’s 709(800) LUT designed to be used with S-Log3 for a moment. This LUT expects middle grey to come in at 41% and it will output middle grey at 43%. It will expect a white card to be at 61% and it will output that same shade of white at a little over 85%. Anything on the S-Log3 side brighter than 61% (white) is considered a highlight and the LUT will compress the highlight range (almost 4 stops) into the output range between 85% and 109% resulting in flat looking highlights. This is all perfectly fine if you expose at the levels suggested by Sony. But what happens if you do expose brighter and try to use the same LUT either in camera or in post production?

Well if you expose 1.5 stops brighter on the log side middle grey becomes around 54% and white becomes around 74%. Skin tones which sit half way between middle grey and white will be around 64% on the LUT’s input. That’s going to cause a problem! The LUT considers anything brighter than 61% on it’s input to be a highlight and it will compresses anything brighter than 61%. As a result on the output of your LUT your skin tones will not only be bright, but they will be compressed and flat looking. This makes them hard to grade. This is why if you are shooting a bit brighter it is much, much easier to grade your footage if your LUT’s have offsets to allow for this over exposure.

If the camera has an EI mode (like the FS7, F5, F55 etc) the EI mode offsets the LUT’s input so you don’t see this problem in camera but there are other problems you can encounter if you are not careful like unintentional over exposure when using the Sony LC709 series of LUTs.

Sony’s  709(800) LUT closely matches the gamma of most normal monitors and viewfinders, so 709(800) will deliver the correct contrast ie. contrast that matches the scene you are shooting plus it will give conventional TV brightness levels when viewed on standard monitors or viewfinders.

If you use any of the LC709 LUT’s you will have a miss-match between the LUT’s gamma and the monitors gamma so the images will show lower contrast and the levels will be lower than conventional TV levels when exposed correctly. LC709 stands for low contrast gamma with 709 color primaries, it is not 709 gamma!

Sony’s LC709 Type A LUT is very popular as it mimics the way an Arri Alexa might look. That’s fine but you also need to be aware that the correct exposure levels for this non-standard LC gamma are middle grey at around 41% and white at 70%.

An easy trap to fall into is to set the camera to a low EI to gain a brighter log exposure and then to use one of the LC709 LUT’s and try to eyeball the exposure. Because the LC709 LUT’s are darker and flatter it’s harder to eyeball the exposure and often people will expose them as you would regular 709. This then results in a double over exposure. Bright because of the intentional use of the lower EI but even brighter because the LUT has been exposed at or close to conventional 709 brightness. If you were to mistakenly expose the LC709TypeA LUT with skin tones at 70%, white at 90% etc then that will add almost 2 stops to the log exposure on top of any EI offset.

Above middle grey with 709(800) a 1 stop exposure change results in an a 20% change in brightness, with LC709TypeA the same exposure change only gives a just over 10% change, as a result over or under exposure is much less obvious and harder to measure or judge by eye with LC709. The cameras default zebra settings for example have a 10% window. So with LC709 you could easily be a whole stop out, while with 709(800) only half a stop.

Personally when shooting I don’t really care too much about how the image looks in terms of brightness and contrast. I’m more interested in using the built in LUT’s to ensure my exposure is where I want it to be. So for exposure assessment I prefer to use the LUT that is going to show the biggest change when my exposure is not where it should be. For the “look” I will feed a separate monitor and apply any stylised looks there. To understand how my highlights and shadows, above and below the LUT’s range are being captured I use the Hi/Low Key function.

If you are someone that creates your own LUT’s an important consideration is to ensure that if you are shooting test shots, then grading these test shots to produce a LUT it’s really, really important that the test shots are very accurately exposed.

You have 2 choices here. You can either expose at the levels recommended by Sony and then use EI to add any offsets or you can offset the exposure in camera and not use EI but instead rely on the offset that will end up in the LUT. What is never a good idea is to add an EI offset to a LUT that was also offset.

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Want to shoot direct to HDR with the PXW-FS7, PMW-F5 and F55?

Sony will be releasing an update for the firmware in the Sony PXW-FS5 in the next few days. This update amongst other things will allow users of the FS5 to shoot to HDR directly using the Hybrid Log Gamma HDR gamma curve and Rec2020 color. By doing this you  eliminate the need to grade your footage and could plug the camera directly in to a compatible HDR TV (the TV must support HLG) and see an HDR image directly on the screen.

But what about FS7 and F5/F55 owners? Well, for most HDR productions I still believe the best workflow is to shoot in S-Log3 and then to grade the footage to HDR. However there may be times when you need that direct HDR output. So for the FS7, F5 and F55 I have created a set of Hybrid Log Gamma LUT’s that you can use to bake in HLG and Rec2020 while you shoot. This gives you the same capabilities as the FS5 (with the exception of the ability to add HLG metadata to the HDMI).

For a video explanation of the process please follow the link to my new Patreon page where you will find the video and the downloadable LUT’s.

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

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: http://www.xdcam-user.com/?s=LUT%27s

Using S-Log2 and S-Log3 with the Sony A6300 (with LUT’s to download).

Sony_A6300 Using S-Log2 and S-Log3 with the Sony A6300 (with LUT's to download).The new Sony A6300 is making quite a stir. This compact interchangeable lens camera has an amazing feature set that is very similar to the features found on it’s bigger brothers the A7sII and A7RII.

As a video camera it’s also capable recording using the XAVC-S codec in  both HD and UHD(4K). It can even shoot at 120fps in HD.  It also has picture profiles so you can tailor the look of the pictures or to suit different shooting conditions. The Cinegammas are very useful for challenging lighting conditions as they offer an improved highlight roll-off. As well as the Cinegammas the camera also has the S-Log2 and S-Log3 log gamma curves as well as S-Gamut, S-Gamut3 and S-Gamut3.cine.

Log gamma curves are very different to conventional gamma curves. Conventional gamma curves (like rec-709 or Cinegamma) are designed to produce a pleasing on screen image without any post production work (although the cinegammas do typically benefit with some tweaking in post). To do this conventional gammas keep the mid-range contrast compatible with conventional TV’s and monitors, so the picture has natural contrast when viewed on a TV. Then to help deal with bright highlights conventional gammas use some kind of highlight roll off or knee to increase the brightness range the camera can capture without effecting the mid range.  Unfortunately this means that the highlights are somewhat compromised, looking very flat, lacking contrast and this is often what gives video the “video look”. In addition it also means that if you are over exposed when you shoot, the picture will look bad and no amount of post production correction will ever make it look good. Most TV camera operators will be very familiar with the phrase “protect your highlights”, meaning don’t over expose, if anything under expose a tiny bit to keep the highlights looking good.

Log gamma curves such as S-Log2 and S-Log3 are very different.  They extended the dynamic range that the camera can capture. To do this they no longer try to be directly compatible with conventional TV’s and monitors and just focus on capturing the biggest possible range. The pictures will be made compatible with the TV or monitor via adjustments made during editing or in post production. So working with S-log2 and S-Log3 is a two step process – shooting and grading (grading is the term used for adjusting the look of an image in post production).

Because log gamma no longer needs to have a contrast range that matches the display range, more dynamic range can be squeezed into a conventional recording codec. It also means that there is no longer a need to use any highlight roll off or knee, so there is a lot more picture information in the highlights and brighter parts of the image. As a result exposing log gamma extra brightly is not normally a problem and in many cases brings lot of advantages. Log gamma curves do have a shadow roll off that mimics the real world shadow roll off. As a result log gammas really don’t like being under exposed, instead they prefer to be over exposed. So unlike conventional gamma where we “protect the highlights” with log gamma you need to “protect the shadows”. Under exposed log looks bad. It will lack color and it will be noisy and grainy.

For most camera operators it’s quite disconcerting to start shooting very slightly over exposed as it goes against everything you’ve learnt about shooting with a conventional video camera. But trust me, shooting 1 to 2 stops brighter than the recommended levels given by Sony on the A6300 (and any other Sony Log camera) will normally bring the best results.

I wrote a guide on how to do this with the Sony A7s here: http://www.xdcam-user.com/2014/08/exposing-and-using-slog2-on-the-sony-a7s-part-one-gamma-and-exposure/

The very same techniques can be used with the A6300, A7SII and A7RII. The A6300 etc also have S-Log3, but as these are 8 bit cameras (even when using an external recorder) I would still recommend that you use S-Log2. Besides, viewing and monitoring S-Log3 is tough as the pictures look even flatter than S-Log3.

If you follow the link below you will find a set of LUT’s (Look Up Tables) that can be applied to A6300 footage in post production to give different looks. There are some film-look LUT’s and 709 (normal TV look) LUT’s and in each case there are LUT’s for normal exposure as well as footage exposed 1 stop and 2 stops brighter. If a LUT name includes “1OVER” this means that the LUT is designed to work with footage that has been exposed 1 stop brighter than the levels given by Sony. My recommendation is to shoot at between 1 and 2 stops bright. For both S-Log2 and S-Log3 this would mean setting zebras to 70% and exposing a piece of white paper so that zebras are just starting to appear on the white paper.

If you find these LUT’s useful please consider buying me a coffee or a beer. I’m not paid to write these articles. For the LUT set I would appreciate a Cocktail, but am happy with whatever you feel is appropriate or affordable.


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pixel Using S-Log2 and S-Log3 with the Sony A6300 (with LUT's to download).

To download the LUT set please click the link: Alisters A6300 Mega LUT Kit

 

Set of 20 Cube LUT’s for the Sony A7S.

I’ve been doing a lot of work on shooting SLog-2 with the A7s. I realised almost straight away that a set of LUT’s for this camera would really help speed up my grading and testing. In addition as the camera is only 8 bit I have found that I am actually getting the best results from the Slog-2 if I over expose it just a little bit, depending of course on the scene. So I created a set of LUT’s that includes compensation for shooting at the nominal correct exposure as well as either 1 or 2 stops over exposed. In all there are 20 LUT’s in two sets. One is Rec-709 based LUT’s and the other Filmic LUT’s to act as starting points for further grading.

I am in the process of creating the complete workflow and SLog-2 guide for the A7s which I should be publishing later next week which will have much more information on how to use these LUT’s. But in the mean time here are the LUT’s if anyone want’s to play (and I would like feedback on what you think of them).

The LUT naming goes something like this:

AC A7S  709(800) ZERO

AC  (That’s me!).    A7S (The Camera).

709(800) = Output gamma or style.     ZERO = Exposure off set.

The exposure offset refers to the number of stops the footage is over exposed by relative to the normal SLog2 exposure level of Middle Grey at 32% and 90% white at 59%. ZERO menas no exposure offset. 1STOP would be used when the SLog2 was exposed 1STOP over and in this case the LUT then shifts the exposure back down 1 stop to compensate.

709 = Vanilla Rec-709, very contrasty, but limited highlight response and hard clip of over exposure.

709(800) = Rec-709 gamma with 800% (high) dynamic range. Will be slightly low contrast but deals much better with over exposure or bright highlights than vanilla 709.

Film-Like1 = An extended range gamma with highlight roll off (+400% range), slightly de-saturated, slightly more film like color (small red/yellow removed).

Filmic2 = Extended range low contrast gamma with very good over exposure handling. Slightly de-saturated. Good grading start point.

Filmic3 = Similar to Filmic2 but a little more contrast at the expense of a little less highlight roll off.

Click on the links below to download the LUT sets. PLEASE DO NOT HOST THESE ELSEWHERE OR DISTRIBUTE THESE ELSEWHERE OR VIA ANY MEANS OTHER THAN A LINK TO THIS PAGE.

Alisters A7S 709 LUTS v2

Alisters A7S Filmic LUTS set1
If you find the LUT’S useful, please consider buying me a beer or a coffee.


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pixel Set of 20 Cube LUT's for the Sony A7S.

Major Update to my Cine-EI guide for the PMW-F55 and PMW-F5

I have just published a major update to my guide to Cine-EI on the PMW-F55 and F5. The guide now goes in to a lot more depth. I have tried to make it easy to understand but it is also quite technical, I have deliberately included the technical background stuff so that hopefully you will understand why Cine-EI and LUT’s work the way they do. I’ve added a whole new section on exposure methods for some of the different LUT’s as well as how to create your own LUT’s.

Please take a look if you use these cameras. Soon I will add a section on post production.

http://www.xdcam-user.com/2013/12/cine-ei-mode-when-recording-s-log23-and-raw-on-the-f5-and-f55/