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'Input color profile' set to Linear not a good idea?

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Guest Deom
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  • Hi all!

     

    I'm working on an interior scene, from an old file, which is supposed to look somewhat photorealistic. Since I wasn't getting the results I was expecting when tweaking the setup I went through the project settings to double check that Linear workflow was activated etc, which it was. But I then noticed the dropdown for the input color profile. Out of curiosity I changed that to Linear and all of a sudden the render looks much more realistic. It goes way brighter but if I turn down the lights it looks great. Even the shaders that does not have any imported textures in them look way better.

     

    So first off I was all happy, but after some googling it seems that it might be a bad idea to work in that mode. Some comments mentioned that the result would be unpredictable and not reliable when viewed on different screens.

     

    I don't understand anywhere near enough about the whole logic behind the LWF workflow to come to a conclusion, so please enlighten me if anyone happens to know..!? Can I work with it set to Linear and "trust" the result when going to post in AE?

     

    Many thanks in advance to whoever can tell me which way to go!

     

    Cheers/Dag

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    At its simplest, the purpose of linear workflow is to make sure the computer sees the same colour as you do.

     

    The basic problem is that you're viewing on a monitor which is not linear but which has a built-in gamma shift. Ordinarily Cinema compensates for this by taking the input values for the colours you choose by eye (in the pickers) in gamma-shifted 'monitor' space and inverting the gamma - which linearises the values, taking them into the space where the render engine does its calculations.

     

    However, if you use the linear input profile setting Cinema will no longer linearise any colour values you input via the picker - it will assume that those are the exact values you want the engine to work with. In the cascade of calculations that result in the final colour of each pixel in the render, the engine will constantly be 'seeing' the colour differently from the way you see it on screen (because you're still viewing with a gamma transform curve applied). This is what introduces the unpredictability - low values are affected more by gamma than high values.

     

    The second thing is that RGB image textures may or may not have embedded profiles and were almost certainly all created in monitor space, with a gamma transform applied. So again, you risk sending the wrong values to the engine for colour images without profiles. Remember, low (dark) values are affected more by gamma than high (bright) values, so the whole tonal balance of the image texture can be thrown out of whack.

     

    Hope that helps - it's not the entirety of LWF, but the relevant bit for your question.

     

    Mark

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    Guest Deom
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  • Thanks for your very educating breakdown Mark!

     

    I've been researching and testing further today and think that I've found a good way to set stuff up and the renders are now looking good. Since I'm still not 100% certain that I understand the pitfalls I'd love it if you can tell me whether or not my current setup is reliable..?

     

    The project is set to Linear workflow with sRGB input color profile rendering in the Physical renderer. I got GI on with an gamma value of 1 and the Color correction effect applied with gamma set to 2.2. For each texture I've then applied a filter in which I gamma compensate to 0.455. After some tweaking of reflections etc things are now closer to what I'm going for. So do you think this is a reliable approach? And are the gamma "hacks" applicable when using the Physical renderer?

     

    Sorry if I'm being a slow catch and thanks again for the help!

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