Replacing an image with a grayscale with transparency one saves the image as DeviceRGB

[SveLil]

If you replace an image in a pdf with a png that is grayscale + transparency, the image will be saved as DeviceRGB in the PDF

page_updated.pdf

This seems to be a problem with the go png library, as the color model that is returned by DecodeConfig is the same for ctGrayscaleAlpha and ctTrueColorAlpha (both return color.NRGBAModel )

[SveLil]

This could be either solved by parsing the image header or by adding a flag "-gray" (similar to import) to force grayscale color space

[hhrutter]

I remember this file....
It involves an Image stream combined with SMasks.

Dealing with transparency and SMasks is not part of pdfcpu currently and needs to be dealt with separately.
It is a quite complex topic actually.

[SveLil]

Interestingly, pdfcpu does handle the SMask and transparency as I would expect.

[hhrutter]

I need to double check for sure not across the board.
We are talking about all relevant usecases.

[SveLil]

Is it ok if I implement this usecase similar to the grayscaling while importing?

[SveLil]

Please let me know if you want anything changed

[hhrutter]

Thanks, I will check it out!