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user22611
Asked: 2018-06-18 08:31:49 +0800 CST

JPGICC: What does the option described as "Precalculates transform" do?

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The man page of jpgicc says -c NUM Precalculates transform (0=Off, 1=Normal, 2=Hi-res, 3=LoRes) [defaults to 1].

I was not able to find more information about that option. To me it seems 1 is a trade-off between speed and quality. But to me, speed does not matter.

What does "Hi-res" mean and why should I prefer it over "Normal" (or why should I prefer "Normal" over "Hi-res")?

color-management photo-management

1 Answers

  1. I must admit I'm not a person that cares much about color accuracy. If colors are different enough between text and background, and I can read the screen, I'm happy.

    7 year old email chain about precalculations

    The differences between no precalculations, normal, low-res and high-res is not just speed but can lead to flaws in the shadows:

    I had Cinepaint set in the color management options to use "don't Precalculate" rather than one of the other Cinepaint options (Low Resolution, High Resolution, CMM default). I wish I had realized that particular setting might make a difference, because it would have saved a lot of time and tedious testing.

    I don't know of any image editing program besides Cinepaint that offers the user the choice to use Low Res, High Res, CMM default, or "Don't Precalculate". I would guess that most or all use something like "CMM default", because I just checked, and Cinepaint, when set to use "CMM default" and "use black point compensation" produces the same halving of the shadow values as all the other image editors.

    At any rate, at this point every image editor that I tested, other than Cinepaint and the latest Krita 2.6 alpha, produces visibly damaged shadow areas if there is a linear gamma profile involved in an ICC profile conversion.

    littleCMS's Author's take on precalculations

    In his .pdf tutorial the author states if there are only a few colors to transform then precalculations can be turned off all together:

    Optimization

    Little CMS tries to optimize profile chains whatever possible. There are some built-in optimization schemes, and you can add new schemas by using a plug-in. This generally improvesthe performance of the transform, but may introduce a small delay of 1-2 seconds when creating the transform. If you are going to transform just few colors, you don't need this precalculations. Then, the flag cmsFLAGS_NOOPTIMIZE in cmsCreateTransform() can be used to inhibit the optimization process. See the API reference for a more detailed discussion of the flags.

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