From 55d589a548cd881c3fe5a94a1c7e2db6a88ae8ea Mon Sep 17 00:00:00 2001 From: Johannes Schauer Marin Rodrigues Date: Sat, 14 Aug 2021 10:19:46 +0200 Subject: [PATCH] README.md: document how to remove alpha channel and --rotation=ifvalid --- README.md | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/README.md b/README.md index 10aeedc..3c3e08a 100644 --- a/README.md +++ b/README.md @@ -80,7 +80,17 @@ Bugs - 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. + and thus, input images must not carry transparency information. You can + remove the alpha channel for example with imagemagick: + + convert input.png -background white -alpha remove -alpha off output.png + + - An error is produced if the input image is broken. This commonly happens if + the input image has an invalid EXIF Orientation value of zero. Even though + only nine different values from 1 to 9 are permitted, Anroid phones and + Canon DSLR cameras produce JPEG images with the invalid value of zero. + Either fix your input images with `exiftool` or similar software before + passing the JPEG to `img2pdf` or run `img2pdf` with `--rotation=ifvalid`. - 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,