README.md: clarify PDF transparency (closes: #76)

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Johannes 'josch' Schauer 2020-05-06 08:55:46 +02:00
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@ -77,10 +77,10 @@ Bugs
files with other colorspaces, you must explicitly specify it using the
`--colorspace` option.
- Input images with alpha channels are not allowed. PDF doesn't support alpha
channels in images and thus, the alpha channel of the input would have to be
discarded. But img2pdf will always be lossless and thus, input images must
not carry transparency information.
- Input images with alpha channels are not allowed. PDF only supports
transparency using binary masks but is unable to store 8-bit transparency
information as part of the image itself. But img2pdf will always be lossless
and thus, input images must not carry transparency information.
- img2pdf uses PIL (or Pillow) to obtain image meta data and to convert the
input if necessary. To prevent decompression bomb denial of service attacks,