Image plugin fails despite correct tile settings #7536

from PIL import Image, ImageFile, ImageStat

def _accept(prefix):
    return prefix[:3] == b"FFF"

def u16(arr, index):
    return int.from_bytes(arr[index:index+2], 'little')

class FFFImageFile(ImageFile.ImageFile):
    format = "FFF"
    format_description = "Raw image exported by FLIR ResearchIR"
    
    def _open(self):
        h = self.fp.read(2780)
        print(h[:16]) #To verify that this is called
        s = u16(h,0x6c)
        self._size = (
            u16(h,s+2),
            u16(h,s+4),
        )
        self._mode = 'I;16L'
        
        self.tile = [('raw', (0,0) + self.size, s+32, (self.mode, 0, 1))]
        print(self.mode)
        

Image.register_open(FFFImageFile.format, FFFImageFile, _accept)

Image.register_extensions(
    FFFImageFile.format,
    [
        ".img", #Single image
        ".seq", #Series of images
    ],
)

def read(fname):
    d = []
    with open(fname, 'rb') as f:
        d = f.read()
    s = u16(d,0x6c)
    size = (
        u16(d,s+2),
        u16(d,s+4),
    )
    mode = 'I;16L'
    im = Image.frombytes(mode,size,d[s+32:],decoder_name='raw')
    im = im.convert(mode='F')
    return(im)

def max_contrast(im, debug=False):
    pmin, pmax = im.getextrema()
    if debug:
        print(f'{pmin}, {pmax}')
    m = 255 / (pmax - pmin)
    b = m * pmin
    im = im.point(lambda x: m*x-b)
    im = im.convert(mode='L')
    if debug:
        stat = ImageStat.Stat(im)
        print(f'min/max: {stat.extrema}')
        print(f'mean: {stat.mean}  stddev: {stat.stddev}')
    return im

if __name__ == '__main__':
    fname = "Snap-000014.img"
    #im = read(fname)
    im = Image.open(fname)
    im = max_contrast(im, True)
    im.show()