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