[GitHub] [pdfbox] Etienne-Gautier opened a new pull request, #150: better deviceCMYK profile

[GitBox]

Etienne-Gautier opened a new pull request, #150:
URL: https://github.com/apache/pdfbox/pull/150

   I noticed that the color conversions were not always accurate for CMYK PDFs. 
I tested some examples and it seems like the default color profile used by 
PDFBox is not a very close match to U.S. Web Coated (SWOP) v2 (which can't be 
used directly for licensing reasons as per the in-code comment).
   
   I have found that the icc profile 
[here](https://github.com/saucecontrol/Compact-ICC-Profiles#cmyk) under 
creative commons CC0 license is much closer visually to U.S. Web Coated (SWOP) 
v2. As stated on their readme, this CMYK profile seems to be designed for the 
purpose of replacing U.S. Web Coated (SWOP) v2 when decoding images that don't 
have an embedded profile:
   
   > The primary purpose of this profile is to serve as a default for image 
viewing or conversion software to use when a CMYK image does not contain an 
embedded profile. It cannot be used for conversion to CMYK or for other 
rendering intents.
   
   Here are a few examples that show the difference between these color 
profiles for the attached PDF [HiAce_online_brochure JAN2021 page 2 
only.pdf](https://github.com/apache/pdfbox/files/10387964/HiAce_online_brochure.JAN2021.page.2.only.pdf)
   With U.S. Web Coated (SWOP) v2 - as opened in Acrobat:
   <img width="260" alt="acrobat screenshot" 
src="https://user-images.githubusercontent.com/25138293/211694418-5d473b09-4b64-498f-965e-cea8fb5a6e66.png";>
   
   With ISOcoated_v2_300_bas.icc (used by PDFBox currently), screenshot taken 
from pdfbox debugger:
   <img width="260" alt="ISO Coated screenshot from pdfbox debugger" 
src="https://user-images.githubusercontent.com/25138293/211694444-c0525feb-42d4-4fed-b07d-5f8358468252.png";>
   
   With CGATS001Compat-v2-micro.icc (proposed change), screenshot taken from 
pdfbox debugger:
   <img width="260" alt="CGATS001 screenshot from pdfbox debugger" 
src="https://user-images.githubusercontent.com/25138293/211694469-7f9db9b8-f90e-4e09-a27e-a6c9dc7882c8.png";>
   


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