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Milan_Michalik
Participating Frequently
May 20, 2013
Question

REC709 and sRGB - no color management difference

  • May 20, 2013
  • 2 replies
  • 46575 views

We know, there is only a gamma difference (to make it simple) between REC709 and sRGB and this gamma difference is quite important for serious work.

I never used color management in AE in the past, because it slowed down the fps for the preview.

Yesterday I wanted to check how it works in CS6 and I found out this:

There is no difference between REC709 and sRGB in color management in After Effects CS6 Win or Mac?

I set the color management on and choose REC709.

I import a footage (I tried every possible format - stills, video, video seq... with or without embeded profiles).

In interpret footage box - if I choose something weird like Film or cieRGB or widegammutRGB, I see the change in the viewer.

But if I am switching between sRGB and REC709, I see no difference.

I see the message, that the gamma will be corrected from 1.9 to 2.2, but it is not happening.

Well... I used the similar concept in Nuke and Smoke and it works there, just I don't know what I am doing wrong in AE ?

And yes, I read all the help files and tutorials 10000x.

Thank you for any ideas in advance.

Milan

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    2 replies

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    paulinventome
    Known Participant
    May 20, 2013

    AFAIK there is a difference between REC709 and sRGB curves, they're not just gamma curves, i can't remember off the top of my head but the shadows flatten out into a linear line with one of them. Whether the difference is enough for you to worry about depends on what you're doing. You can see the LUTs in Nuke on the project settings and compare the curves.

    There should be a difference applying a REC709 vs sRGB profile on injest. Are you in 32 bit float project mode? Your viewing LUT/profile is set to sRGB? What is the footage and format you're importing? Is there something in that footage that is overriding your selection?

    You can also not apply a profile on injest and apply one via an effect afterwards, perhaps try that to see if you can see it working

    Sometimes AE attempts to be a little too clever and automatic, whereas Nuke tends to leave it up to you and not 'auto decide' anything.

    hth

    paul

    M
    Milan_MichalikAuthor
    Participating Frequently
    May 20, 2013

    Hi, finally someone who is with me :-) and I see that you asks good questions :-)

    I know that there is more difference then the gamma (this is why I wrote: make it simple) in my first topic.

    "Is there something in that footage that is overriding your selection?"

    Right question. This is what I am asking too. But I've tried all codecs and all formats, even stills, with embeded and non-embeded profiles. What should I test more?

    "Are you in 32 bit float project mode?"

    I tried 8bits, 16bits and 32float too.

    "Your viewing LUT/profile is set to sRGB?"

    Just right now my windows monitor is set to sRGB, my After Effects color management is set to sRGB. And my footage is REC709. So I see it's too dark in sRGB color space, I see less resolution in blacks and my picture is darker.

    I opened AE and Nuke on the same time, same computer, same monitor, same footage.

    I set sRGB for Nuke and AE as a color space. Viewing color space is sRGB on both.

    Read node in NUKE: colorspace sRGB = picture is darker, colorspace REC709 = picture is correct.

    Import interpret footage AE: colorspace sRGB = picture is darker, colorspace REC709 = picture is darker, no change

    THERE iS EVEN MORE !

    If I set simulate output view to REC709 instead of sRGB, my AE composition stills the same.

    If I do the same in NUKE, it changes of course.

    I see I have to build a LUT and use this workflow in AE, just I wonder that I am alone in the world who cares about this problem???

    I am not an NUKE artist or employee, who wants to promote NUKE, or other application. I own After Effects and I want to use it in a right way.

    5 minutes ago I tried the same on Mac = same problem Win/Mac = so it isn't my computer fault.

    So the question is: Is there anybody who sees a difference in the picture when you injest (import) a footage in 2 different ways, first as a sRGB and then as a REC709???

    Bob Currier
    Bob Currier
    Participating Frequently
    May 20, 2013
    Fuzzy: Nuke, very simple.

    And which difficulties exactly are you facing in AE?

    I double checked and it's sRGB that flattens out at the bottom of the curve, it does make a difference, subtle but it's there.

    And how does it contradict with or append to the definition, which states that sRGB has 2.2 gamma and Rec.709 - 1.9? Do you understand what that curve represents?


    Pedantry ahead! This doesn't directly address Milan's situation, but there is a bit too much oversimplification going on here for my taste.

    Neither Rec.709 nor sRGB have simple power function "gamma" curves. Both include a flattened section near black to avoid the asymptotic nature of a straight power function.

    Rec.709 uses a power function of 0.45 (1/0.45 = 2.2), but includes a linear portion with a slope of 4.5 below the tristimulus value of 0.018. This gives it an actual transfer curve approximating a power curve of 0.5. This is at the encoding (camera) end of things. Rec.709 the assumes the display will have a power curve of 2.5. This gives an end-to-end reproduction of 1.25, which is subjectively correct, although it is not mathematically linear. And to further confuse things, most current television sets have a power function of 2.6 or higher.

    sRGB similarly uses a power function of 0.42 (1.0/0.42 = 2.38), but also includes a linear portion, giving an overall transfer function approximating a pure power function of 0.45. Assuming the same display as with Rec.709 (with a power function of 2.5), then end-to-end reproduction is 1.125. This is considerably lower than with Rec.709, and is intended to compensate for the fact that computer screens are typically viewed with higher ambient lighting than televisions. It was the intent of the sRGB standard creators that images not only look the same on different computers and monitors, but also that sRGB images on the computer (high ambient light) should give the same subjective contrast experience as Rec.709 images viewed on a television (low ambient light).

    Given that most people calibrate their monitor to 2.2 instead of 2.5, things are already broken. And certain expensive name-brand HD video monitors still use Rec.601 constants. Sigh...

    Mylenium
    Mylenium
    Legend
    May 20, 2013

    Well, but do you actually use color management onb your system, i.e. a monitor profile?

    Mylenium

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    Milan_MichalikAuthor
    Participating Frequently
    May 20, 2013

    Yes, I do. I use sRGB monitor profile - because my monitor is not REC709, but sRGB. Just I do not understand, why you are asking this question :-)

    Again, on the same system, in NUKE, when I set my project as sRGB and when I switch my input footage to REC709 instead of sRGB, I see the difference in gamma.

    When I do the same in AE, I don't see the difference. REC709 or sRGB - the same.

    Mylenium
    Mylenium
    Legend
    May 20, 2013

    Well, working with color profiles makes no sense on an unmanaged system, that's why. Do you actually assign the profile for comp preview/ use it in Nuke? As far as I'm concerned, I see nothing wrong here. Seems more to me like you are working unmanaged in Nuke and are misinterpreting it's lack of Gamma compensation for how things should look in AE...

    Mylenium

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