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https://issues.apache.org/jira/browse/PDFBOX-6260?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18117280#comment-18117280
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valery edited comment on PDFBOX-6260 at 9/20/26 12:13 PM:
----------------------------------------------------------
Hi, [~tilman].
A follow-up question about PDCalGray, related to the chromatic adaptation added
here. No bug is confirmed; I only want to know whether one exists.
PDCalGray.toRGB() calibrates only when the whitepoint is exactly (1 1 1).
For any other whitepoint it skips the calibration and returns
{value[0], value[0], value[0]}, so gamma is ignored:
if (isWhitePoint()) // only (1,1,1)
... convXYZtoRGB(powAG, powAG, powAG)
else
return new float[] { value[0], value[0], value[0] };
This looks like the workaround from PDFBOX-2971 ("treat CalGray like CalRGB").
The reporter there diagnosed the missing D50 adaptation, which PDFBOX-6260 has
now added. I did a numeric check of calibrated + adapted CalGray against the
skip, as 8-bit gray:
- the whitepoint no longer matters, because it cancels out in the adaptation;
only gamma matters
- gamma 2.2: at most 7/255 different from the skip (mostly dark tones, e.g.
value 0.1 gives 19 vs 26), so PDFBOX-2971's D65 / gamma 2.2 file looks fine
either way
- gamma 1.0: up to 73/255 different; gamma 1.8: up to 18; gamma 3.0: up to 30
So the skip should only be visible for a CalGray with a whitepoint other than
(1 1 1) and a gamma clearly different from 2.2. I searched the test corpus,
JIRA and the pdf.js test files. I only found CalGray with D65 / 2.2
(PDFBOX-2971) and with (1 1 1) (PDFBOX-4119, 1724, 4750, and pdf.js calgray.pdf
with gamma 1.0 and 5.0). I found no file that renders wrongly.
Two questions:
1. Do you have (or know of) a file with a CalGray that has a non-(1 1 1)
whitepoint and a gamma other than 2.2 and renders wrongly (compared with
Acrobat)? A link would let me test.
2. If not, is the skip still needed for CalGray?If a proper fix is wanted, it
would calibrate always, using (wpX*Y, wpY*Y, wpZ*Y) as XYZ instead of (Y, Y,
Y), which is only correct for whitepoint (1 1 1) today.
was (Author: vbokov):
Hi, [~tilman].
A follow-up question about PDCalGray, related to the chromatic adaptation added
here. No bug is confirmed; I only want to know whether one exists.
PDCalGray.toRGB() calibrates only when the whitepoint is exactly (1 1 1).
For any other whitepoint it skips the calibration and returns
{value[0], value[0], value[0]}, so gamma is ignored:
'''
if (isWhitePoint()) // only (1,1,1)
... convXYZtoRGB(powAG, powAG, powAG)
else
return new float[] { value[0], value[0], value[0] };
'''
This looks like the workaround from PDFBOX-2971 ("treat CalGray like CalRGB").
The reporter there diagnosed the missing D50 adaptation, which PDFBOX-6260 has
now added. I did a numeric check of calibrated + adapted CalGray against the
skip, as 8-bit gray:
- the whitepoint no longer matters, because it cancels out in the adaptation;
only gamma matters
- gamma 2.2: at most 7/255 different from the skip (mostly dark tones, e.g.
value 0.1 gives 19 vs 26), so PDFBOX-2971's D65 / gamma 2.2 file looks fine
either way
- gamma 1.0: up to 73/255 different; gamma 1.8: up to 18; gamma 3.0: up to 30
So the skip should only be visible for a CalGray with a whitepoint other than
(1 1 1) and a gamma clearly different from 2.2. I searched the test corpus,
JIRA and the pdf.js test files. I only found CalGray with D65 / 2.2
(PDFBOX-2971) and with (1 1 1) (PDFBOX-4119, 1724, 4750, and pdf.js calgray.pdf
with gamma 1.0 and 5.0). I found no file that renders wrongly.
Two questions:
1. Do you have (or know of) a file with a CalGray that has a non-(1 1 1)
whitepoint and a gamma other than 2.2 and renders wrongly (compared with
Acrobat)? A link would let me test.
2. If not, is the skip still needed for CalGray?If a proper fix is wanted, it
would calibrate always, using (wpX*Y, wpY*Y, wpZ*Y) as XYZ instead of (Y, Y,
Y), which is only correct for whitepoint (1 1 1) today.
> CalRGB color regression
> -----------------------
>
> Key: PDFBOX-6260
> URL: https://issues.apache.org/jira/browse/PDFBOX-6260
> Project: PDFBox
> Issue Type: Bug
> Components: Rendering
> Affects Versions: 2.0.37, 3.0.8 PDFBox
> Reporter: Tilman Hausherr
> Assignee: Tilman Hausherr
> Priority: Minor
> Labels: CalRGB
> Fix For: 2.0.38, 3.0.9 PDFBox, 4.0.0
>
> Attachments: PDCIEDictionaryBasedColorSpace.java,
> gs-bugzilla686749-CalRGB-reduced.pdf
>
>
> This is about this "unrealistic" CalRGB file of this GS issue
> https://bugs.ghostscript.com/show_bug.cgi?id=686749
> Rendering has different colors since PDFBOX-5079.
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