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You are here: Home / The Last Word / Sequential color space conversions at varying precision

Sequential color space conversions at varying precision

October 8, 2014 JimK Leave a Comment

I am now spreading my color space net to include a wide variety of possible RGB working color spaces. I picked 13 for testing:

  1. IEC 61966-2-1:1999 sRGB
  2. Adobe (1998) RGB
  3. Beta RGB
  4. Bruce RGB
  5. CIE RGB
  6. ColorMatch RGB
  7. Don-4 RGB
  8. ECI RGB v2
  9. Joe Holmes’ Ektaspace PS5
  10. PAL/SECAM RGB
  11. ProPhoto RGB
  12. SMPTE-C RGB
  13. Wide Gamut RGB

If you’re curious about the details of any of these, go to Bruce LIndbloom’s RGB color space page and get filled in.

I wrote a program to take an image of all 16+ million possible colors in SRGB and map it into an sRGB image that is within the gamut of all of the above color spaces. More on how I did that in a subsequent post.

Then I wrote a program to convert the image to sRGB, the first on on the above list, and convert that image to all the other color spaces on the above list in list order. Then it moved on to the next color on the list, and did the same thing again. And again, and again, until it reached the bottom of the list. It skipped the conversions to the source color space. That gave me 13*12, or 156 conversions. I set up the program so that it would either leave the image in double-precision floating point after the conversions, or quantize it to integers whose precision I could choose. Then I computed some stats.

Here’s the result of leaving the converted images in 64-bit floating point:

16MseqFP

Some conversions produce greater errors than others, but all the errors are very small, being much less than one-trillionth of a DeltaE

If we convert each image to 16-bit unsigned integer representation after each conversion, we get this:

16Mseq16bit

The errors are all under one-thousandth of a CIELab DeltaE.

With conversion to 8-bit unsigned integer representation after each conversion:

16Mseq8bit

Now we have mean errors of 1/3 of a DeltaE, and worst-case errors of about 2 DeltaE. You definitely want to be careful when converting color spaces if you’re working with 8-bit images.

I expected that some RGB color space conversions would be more prone to error than others, and that turns out to be the case. What surprises me is how small the differences are — one binary order of magnitude covers them all.

The Last Word

← Color space conversion errors with ProPhoto RGB — 15 bits Chained color space conversion errors with many rgb color spaces →

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