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clarify that input with an alpha channel requires additional computation (closes: #142)

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Johannes Schauer Marin Rodrigues 2022-04-07 17:13:16 +02:00
parent e8ca53738f
commit 3b117e674b
Signed by untrusted user: josch
GPG key ID: F2CBA5C78FBD83E1
2 changed files with 11 additions and 11 deletions
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18
README.md
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@ -27,15 +27,15 @@ software, because the raw pixel data never has to be loaded into memory.
The following table shows how img2pdf handles different input depending on the
input file format and image color space.
| Format | Colorspace | Result |
| -------------------- | ------------------------------ | ------------- |
| JPEG | any | direct |
| JPEG2000 | any | direct |
| PNG (non-interlaced) | any | direct |
| TIFF (CCITT Group 4) | monochrome | direct |
| any | any except CMYK and monochrome | PNG Paeth |
| any | monochrome | CCITT Group 4 |
| any | CMYK | flate |
| Format | Colorspace | Result |
| ------------------------------------- | ------------------------------ | ------------- |
| JPEG | any | direct |
| JPEG2000 | any | direct |
| PNG (non-interlaced, no transparency) | any | direct |
| TIFF (CCITT Group 4) | monochrome | direct |
| any | any except CMYK and monochrome | PNG Paeth |
| any | monochrome | CCITT Group 4 |
| any | CMYK | flate |
For JPEG, JPEG2000, non-interlaced PNG and TIFF images with CCITT Group 4
encoded data, img2pdf directly embeds the image data into the PDF without

4
src/img2pdf.py
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@ -1823,8 +1823,8 @@ def read_images(rawdata, colorspace, first_frame_only=False, rot=None):
smaskidat, _, _ = to_png_data(a)
logger.warning(
"Image contains an alpha channel which will be stored "
"as a separate soft mask (/SMask) image in PDF."
"Image contains an alpha channel. Computing a separate "
"soft mask (/SMask) image to store transparency in PDF."
)
elif color in [Colorspace.P, Colorspace.PA] and iccp is not None:
# PDF does not support palette images with icc profile