Extract some transparent PNG images, discoloration occurs

[mc373906408]

def recoveImage(xref, smake):
            def getimage(pix):
                if pix.colorspace.n != 4:
                    return pix
                tpix = fitz.Pixmap(fitz.csRGB, pix)
                return tpix

            pix1 = fitz.Pixmap(self.mu_Document, xref)
            pix2 = fitz.Pixmap(self.mu_Document, smake)


            pix = fitz.Pixmap(pix1)
            pix.setAlpha(pix2.samples)
            pix1 = pix2 = None

            return getimage(pix)

The original image：

Extracted image：

[JorjMcKie]

The logic to recover the alpha channel is known to be incomplete.
I am still investigating which cases need to be differentiated - so I will remove the bug label and label this as enhancement.
In your special case, this should help:

def recoveImage(xref, smake):
    def getimage(pix):
        if pix.colorspace.n != 4:
            return pix
        tpix = fitz.Pixmap(fitz.csRGB, pix)
        return tpix

    pix1 = fitz.Pixmap(self.mu_Document, xref)
    pix2 = fitz.Pixmap(self.mu_Document, smake)
    pix = fitz.Pixmap(pix1, 1)  # add alpha channel
    ba = bytearray(pix2.samples)
    for i in range(len(ba)):
        if ba[i] > 0:
            ba[i] = 255
    pix.setAlpha(ba)
    pix1 = pix2 = None
    return getimage(pix)

[mc373906408]

I will temporarily use PIL to restore transparency, looking forward to improvement

[JorjMcKie]

Ah, ok.
Can you please let me know which PIL feature was a help / solved the problem?

[mc373906408]

from PIL import Image

             ...

            pix1 = fitz.Pixmap(self.mu_Document, xref)
            pix2 = fitz.Pixmap(self.mu_Document, smake)

            mode="RGB"
            if pix1.alpha>0:
                mode="RGBA"
            pix=Image.frombytes(mode,(pix1.irect[2],pix1.irect[3]),pix1.samples)
            mask=Image.frombytes("L",(pix2.irect[2],pix2.irect[3]),pix2.samples)
            tpix=Image.new("RGBA",pix.size)
            tpix.paste(pix,None,mask)
            bf=BytesIO()
            tpix.save(bf,"png")
            
            return bf.getvalue()

[JorjMcKie]

Great, thanks.
I regard this whole business as being outside PyMuPDF scope. The base C library, MuPDF, also offers no solution here.
The image extraction scripts in the PyMuPDF-Utilities repo are examples, no solutions, for which I can take on responsibility.
Nevertheless I will test your solution a bit more and then modify the script accordingly.
Why re-inventing the wheel if we have Pillow?

[mc373906408]

OK

[JorjMcKie]

I have changed the example scripts extract-imga.py and extract-imgb.py to make use of PIL/Pillow in case of transparent images.