Tag Archives: color

Adjusting the Color marix

Every now and again I get asked how to adjust the color matrix in a video camera. Back in 2009 I made a video on how to adjust the color matrix in the Sony’s EX series of cameras. This video is just as relevant today as it was then. The basic principles have not changed.

The exact menu settings and menu layout may be a little different in the latest cameras, but the adjustment of the matrix setting (R-G, G-R etc) have exactly the same effect in the latest camera that provide matrix adjustments (FS7, F5, F55 and most of the shoulder mount and other broadcast cameras). So if you want a better understanding of how these settings and adjustment works, take a look at the video.

I’ll warn you now that adjusting the color matrix is not easy as each setting interacts with the others. So creating a specific look via the matrix is not easy and requires a fair bit of patience and a lot of fiddling and testing to get it just right.

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Will a bigger recording Gamut give me more picture information?

The short answer is it all depends on the camera you are using. With the F55 or F65 then S-Log2/S-Gamut and S-Log3/S-Gamut3 will give you a larger range of colours in your final image than S-Log3/S-Gamut3.cine. But if you have a PMW-F5, PXW-FS7 or PXW-FS5 this is not going to be the case.

What is Gamut?

The word Gamut means the complete range or scale of something. So when we talk about Gamut in a video camera we are talking about dynamic range and color range (colorspace) taken together. Then within the Gamut we can break that down into the dynamic range or brightness range which is determined by the gamma curve and the color range which is determined by the colorspace.

Looking at the current Sony digital cinema cameras you have a choice of 3 different gamuts when the camera is in log mode plus a number of conventional gamuts you get when shooting rec-709, rec-2020 or any other combination of rec-709 color with cinegammas or hypergammas.

Log gamma and gamuts.

But it’s in the log mode where there is much confusion. When shooting with log with the current cameras you have 3 recommended combinations.

S-Gamut (S-Gamut colorspace + S-log2 gamma).

S-Gamut3 (S-Gamut3 colorspace + S-Log3 gamma).

S-Gamut3.cine (S-Gamut3.cine colorpace + S-Log3 gamma).

The S-log2 and S-log3 gamma curves both capture the same dynamic range – 14 stops, there is no difference in the dynamic range captured.

In terms of the range of colors that can be recorded S-Gamut and S-Gamut3 are the same size and the largest recording colorspaces the cameras have. S-Gamut3.cine is a smaller colourspace but still larger than P3 (digital cinema projection) or rec-709.

Gamuts-only Will a bigger recording Gamut give me more picture information?

But those were all designed for the F55 and F65 cameras that have extremely high quality (expensive) colour filters on their sensors. The reality is that the F5/FS7/FS5 sensor cannot see the full range of any of the S-Gamut colorspaces so in reality you gain very little by using the larger versions. Don’t expect to see a noticeably greater range of colours than any of the other colour modes if you have the F5/FS7/FS5. But all the LUT’s designed for these cameras are based on the S-Gamuts and if you want to mix an FS5 with an F55 in one production it helps to use the same settings so that grading will be easier. It is worth noting at this point that most natural colors do fall within Rec-709, so while it is always nicer to have a bigger color range it isn’t the end of the world for most of what we shoot.

S-Log3 is a great example of what it means to have a bigger recording range than the camera can “see”. S-log3 is based on the Cineon film transfer log gamma curve developed back in the late 1980’s. Cineon was carefully tailored to match film response and designed around 10 bit data (as that was state of the art back then). It allows for around 16 stops of dynamic range. Much later, Arri and many others then adapted Cineon for use in video cameras – The “C” in Arri’s LogC stands for Cineon.

When Sony started doing wide dynamic range cameras they developed their own log gammas starting with S-Log, then S-Log2. These curves are matched very precisely to the way a video sensor captures a scene rather than film. In addition they are matched to the sensors actual capture range, S-Log can record 13 stops as that’s what the sensors in the cameras with S-Log can see. Then S-Log2 is 14 stops as the second generation cameras can all see 14 stops. As a result of being purpose designed for a video sensor, when using S-Log2 you maximise the entire recording range because the sensor is matched to the log which is matched to the record range.

But, these curves drew much criticism from early adopters and colorists because they were very different from the Cineon curve and all the other log curves based on this old school film curve. Colorists didn’t like it because none of their old Cineon LUT’s would work as expected and it was “different”.

S-log-levels Will a bigger recording Gamut give me more picture information?
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-Log3 record to different peak levels.

In response to this Sony then developed S-Log3 and surprise, surprise – S-log3 is based on Cineon. So S-log3 is based on a 16 stop film transfer curve, but the current cameras can only see 14 stops. What this means is that the top 14% of the gamma curve is never used (that’s where stops 15 and 16 would reside) and as a result s-Log3 tops out at 92% and never gets to the 107% that S-Log2 can reach. If Sony were to release a 16 stop camera then S-Log3 could still be used and then it would reach 107%.

Coming back to colorspace. If you understand that the sensor in the F5/FS7/FS5 cannot see the full colour range that S-Gamut or S-Gamut3 are capable of recording then you will appreciate that like S-log3 (that is larger than the camera can see and therefore part empty) many of the possible code values available in S-Gamut are left empty. This is a waste of data. So from a colourspace point of view the best match when shooting log for these cameras is the slightly smaller colorspace S-Gamut3.cine. But S-Gamut3.cine is meant to be matched with S-Log3 which as we have seen wastes data anyway. If the camera is shooting using a 10 bit codec such as XAVC-I or XAVC-L in HD there are plenty of code values to play with, so a small loss of data has little impact on the final image. But if you are recording with only 8 bit data, for example XAVC-L in UHD then this does become much more of a problem and this is when you will find that S-Gamut with S-Log2 is going to give a better result as S-Log2 was designed for use with a video sensor from day 1 and it maximises the use of what little data you have.

So, if I can hack an F5 for 4K, can I also get the F55’s color gamut?

So, we have seen that it is possible to trick an F5 into thinking its an F55 by altering an all file from the F5 and adding some F55 4K settings. This enables 4K internal recording and 4K output over HDMI on the F5. Internal 4K is one of the key differences between the lower cost F5 and the much more expensive F55. Another major difference is that the F55 has a global shutter so no CMOS image skew or other rolling shutter artefacts and the F55 has a larger colour gamut allowing better colour rendition and capture.

A question that has been asked is: Well if we can get 4K, can we also enable the larger colour gamut? One thing we do know is that the sensor used in the F55 is different to the sensor in the F5 as the sensor is replaced if you upgrade your F5 to an F55.

A cameras gamut is determined more by the sensors colour filters than the recording gamut. The recording gamut is like a bucket, the sensor a scoop. If the scoop isn’t big enough you won’t fill the bucket.

The color filters on the F55 are very different to those in the F5, so the F55 can capture a much greater gamut than the F5.

If you think about it, if you hold a red gel up infront of your eyes you will only see an extremely narrow colour gamut, just a single narrow part of the red spectrum. Imagine if you have a red, green and blue filter, you will now see a bit of red, a bit of green and a bit of blue. But you might only see a very narrow part of the full blue spectrum or a very narrow part of red or of green, you won’t see the full spectrum or a large gamut, just narrow slithers of it. The trick is to make filters that are wide enough and with the righ charcteristics to pass all of the R, G and B spectrum but sharply cut off unwanted colors, infra-red or UV at the exactly the right point. This is very hard to do. So the quality and accuracy of the color filters determines both the gamut and the precision of the colors that the camera can capture.

In practice it can be hard to see this difference as none of the monitors available today can show the full gamut that the F55 can capture so you can’t directly see it. But it does make a difference in post as the F55 is able to separate subtle hues more accurately and capture an extended tonal range, for example very subtle differences in skin tones that may be lost on a camera with poorer filters. This means when grading you are able to draw more tonal information out of the image when you transform the color space in to Rec 709 or DCI-P3 and it results in a more natural looking image.

The F5’s sensor gamut is probably somewhere around the size of DCI P3, maybe a bit bigger, but it’s clearly not as big as the F55’s. In addition the colour precision is not as great so some subtle tones are lost. It’s not a massive difference and the F5 does a great job. It’s not something that can be changed with software, it’s all down to the sensor hardware. The F5 just can’t fill the S-Gamut recording bucket so by using S-Gamut your wasting a lot of data. By using a smaller recording gamut like S-Gamut3.cine you can more effectively fill the bucket and make better use of the data available to you.

EX1 and EX3 Picture Profiles.

These are the picture profiles that I am currently tending to favour for the EX1, EX1R and EX3. Please remember that picture profiles are entirely subjective. These settings work for me, that doesn’t mean they are perfect or for everyone. I like the images the cameras produce when I use these profiles. Please feel free to adapt them or modify them any way you choose. They work on any of the current EX cameras.

Vivid – Designed to help match the EX to a PDW-700. Gives vivid colours with a small shift away from yellow.

Matrix – Cinema, Matrix Level +60

R-G +8,  R-B +10,  G-R 0,  G-B +15,  B-R +5,  B-G +6

Detail Level -10 Frequency +20, Crispening -40 (if using gain use crispening +14)

Gamma Cinegamma 1

Black level -3, Black Gamma -35

Low Key Saturation -10

Natural C4 – Designed to give a neutral, natural looking image.

Matrix – Cinema, Matrix Level +35

Detail level -7, Frequency +30, Crispening -40 (if using gain use crispening +20)

Black Level -3, Low key Saturation -15

AC Punch – Gives a very high contrast, bold look.

Matric – Cinema, level +40

Gamma Standard 2, Knee level 80, Slope 0

R-G 0,  R-B +1,  G-R +12,  G-B +2,  B-R +11,  B-G 0

Detail Level -10, Frequency +30, Crispening -45

Black Level -4, Black Gamma -20.

AC Good to Grade – a general purpose setup to give good grading possibilities.

Matrix – Cinema, Level +25

Gamma Cinegamma 1 (Do not use -3db gain)

Detail Level -7, Frequency +45, Crispening -45 (use +35 if using gain)

Black Level -3.

AC-SD Camera look. To mimic an older SD camcorder based on a DSR400, good for HD to SD conversion.

Matrix – Cinema, Level +15

Detail Level +20, Detail Frequency -35, White Limit +35, Black limit +45

Knee, Manual, Level 90, Slope 0.

Gamma Standard 2, Gamma Level +5

Black Gamma -10

Black Level -10

 

 

Enjoy! Any feedback or suggestions welcome. Let me know of any profiles that you come up with that may be of interest to others.

 

The relationship between White Balance and the Matrix.

So… you want to change the look of the colour in your pictures but are not sure how to do it. One of the first things that you need to understand is the relationship between white balance and the colour matrix. They are two very different things, with two different jobs. As it’s name applies white balance is designed to ensure that whites with the image are white, even when shooting under lighting of different colour temperatures. When you shoot indoors under tungsten lights (you know, the one the EU have decided you can no longer buy) the light is very orange. When you shoot outside under sunlight the light is very blue. Our eyes adjust for this very well, so we barely notice the difference, but an electronic video camera is very sensitive to these changes. When you point a video camera at a white or grey card and do a manual white balance, what happens is that the camera adjusts the gain of the red, blue and green channels to minimise the amount of colour in areas of white (or grey) so that they do in fact appear white, ie with no colour. So the important thing to remember is that white balance is trying to eliminate colour in whites and greys.

The Matrix however deals purely with saturated parts of the image or areas where there is colour. It works be defining the ratio of how each colour is mixed with it’s complimentary colours. So changing the white balance does not alter the matrix and changing the matrix does not alter the white balance (whites will still be white). What changing the matrix will do is change the hue of the image, so you could make greens look bluer for example or reds more green.

So if you want to make your pictures look warmer (more orange or red) overall, then you would do this by offsetting the white balance, as in a warm picture your whites would appear warmer if they are slightly orange. This could be done electronically by adding an offset to the colour temperature settings or by using a warming card, which is a very slightly blue card. If you want to make the reds richer in your pictures then you would use the matrix as this allows you to make the reds stronger relative to the other colours, while whites stay white.

PDW 700 Native White Balance

The PDW-700 cameras are balanced for daylight optically and then corrected electronically for tungsten etc.

Traditionally cameras were balanced for Tungsten and then added colour correction optical filters to get to daylight. This was done as CC filters absorb light and thus make the camera less sensitive. Normally when shooting outdoors in daylight sensitivity is not an issue while shooting indoors under tungsten light you used to need every bit of sensitivity you could get.

The down side to this approach is that tungsten contains very little blue light so to get a natural picture the blue channel was often running at quite a high level of gain which increases noise in the blue channel and thus overall noise. In addition when you rotated in the CC filters to get to daylight the sensitivity of the camera was reduced, so you did not have constant gain.

With the PDW-700 (and also the F350 I believe) the cameras are essentially balanced for daylight, without the use of any CC filters, which helps reduce noise in the blue channel. Then for tungsten shooting you electronically re balance the camera. By doing this the overall sensitivity of the camera is constant whether shooting at 3.2K or 5.6K and you only get additional blue channel noise while shooting under tungsten. If you are worried by blue channel noise you can always correct from daylight down to tungsten with an optical CC filter (80A) and leave the camera set to daylight, although this will reduce the systems overall sensitivity by around 1 and a half stops.