pypng >= 0.0.20 Removed 3D support from_array

[gentaman]

I found the error while I was running the bellow like code with jupyter-innotater==0.2.2.

import io

import png
import numpy as np

print(png.__version__, np.__version__)

npim = np.zeros((256, 256, 3), dtype=np.uint8)
npim[:, :, 0] = 255
npim[:, ::8, 1] = 255
npim[:, 1::8, 1] = 255
npim[:, 2::8, 1] = 255

pngbytes = io.BytesIO()
pngmode = 'L' # Greyscale
if len(npim.shape) == 3:
    if npim.shape[2] > 4:
        raise Exception("Image numpy array appears to have more than 4 channels")
    pngmode = ('L','LA','RGB','RGBA')[npim.shape[2]-1]
else:
    npim = np.expand_dims(npim, axis=-1) # Need a third axis for channel
   

pngim = png.from_array(npim, mode=pngmode) # Don't have BGR available so flipped to RGB above
pngim.write(pngbytes) if hasattr(pngim, 'write') else pngim.save(pngbytes) # PyPNG API due to change after v0.0.19
pixel_value = pngbytes.getvalue()
pngbytes.close()

png.__version__='0.20220715.0' np.__version__='1.23.4'

---------------------------------------------------------------------------
ProtocolError                             Traceback (most recent call last)
Cell In [11], line 20
     16 # h, w, ch = npim.shape
     17 # npim = npim.reshape(h, w * ch)
     19 pngim = png.from_array(npim, mode=pngmode) # Don't have BGR available so flipped to RGB above
---> 20 pngim.write(pngbytes) if hasattr(pngim, 'write') else pngim.save(pngbytes) # PyPNG API due to change after v0.0.19
     21 pixel_value = pngbytes.getvalue()
     22 pngbytes.close()

File /app/venv/lib/python3.9/site-packages/png.py:1320, in Image.write(self, file)
   1309 """Write the image to the open file object.
   1310 
   1311 See `.save()` if you have a filename.
   (...)
   1316 cannot be streamed again.
   1317 """
   1319 w = Writer(**self.info)
-> 1320 w.write(file, self.rows)

File /app/venv/lib/python3.9/site-packages/png.py:668, in Writer.write(self, outfile, rows)
    665     a = array(fmt, itertools.chain(*check_rows(rows)))
    666     return self.write_array(outfile, a)
--> 668 nrows = self.write_passes(outfile, check_rows(rows))
    669 if nrows != self.height:
    670     raise ProtocolError(
    671         "rows supplied (%d) does not match height (%d)" %
    672         (nrows, self.height))

File /app/venv/lib/python3.9/site-packages/png.py:703, in Writer.write_passes(self, outfile, rows)
    700 elif self.bitdepth == 16:
    701     rows = unpack_rows(rows)
--> 703 return self.write_packed(outfile, rows)

File /app/venv/lib/python3.9/site-packages/png.py:738, in Writer.write_packed(self, outfile, rows)
    735 # raise i scope out of the for loop. set to -1, because the for loop
    736 # sets i to 0 on the first pass
    737 i = -1
--> 738 for i, row in enumerate(rows):
    739     # Add "None" filter type.
    740     # Currently, it's essential that this filter type be used
    741     # for every scanline as
    742     # we do not mark the first row of a reduced pass image;
    743     # that means we could accidentally compute
    744     # the wrong filtered scanline if we used
    745     # "up", "average", or "paeth" on such a line.
    746     data.append(0)
    747     data.extend(row)

File /app/venv/lib/python3.9/site-packages/png.py:658, in Writer.write.<locals>.check_rows(rows)
    655     wrong_length = False
    656 if wrong_length:
    657     # Note: row numbers start at 0.
--> 658     raise ProtocolError(
    659         "Expected %d values but got %d values, in row %d" %
    660         (vpr, len(row), i))
    661 yield row

ProtocolError: ProtocolError: Expected 255 values but got 256 values, in row 0

I checked that latest pypng.from_array is unsupported 3D ndarray.

https://gitlab.com/drj11/pypng/#release-0020

So I made a simple patch code and check that it work.

print(f"{png.__version__=} {np.__version__=}")

npim = np.zeros((256, 256, 3), dtype=np.uint8)
npim[:, :, 0] = 255
npim[:, ::8, 1] = 255
npim[:, 1::8, 1] = 255
npim[:, 2::8, 1] = 255

pngbytes = io.BytesIO()
pngmode = 'L' # Greyscale
if len(npim.shape) == 3:
    if npim.shape[2] > 4:
        raise Exception("Image numpy array appears to have more than 4 channels")
    pngmode = ('L','LA','RGB','RGBA')[npim.shape[2]-1]
else:
    npim = np.expand_dims(npim, axis=-1) # Need a third axis for channel
    
h, w, ch = npim.shape
npim = npim.reshape(h, w * ch)
npim = np.ascontiguousarray(npim)

pngim = png.from_array(npim, mode=pngmode) # Don't have BGR available so flipped to RGB above
pngim.write(pngbytes) if hasattr(pngim, 'write') else pngim.save(pngbytes) # PyPNG API due to change after v0.0.19
pixel_value = pngbytes.getvalue()
pngbytes.close()

This error only occurs when opencv-python was not installed.

If you want to fix the error, I think that you need to fix the pypng version to 0.0.19 or fix the jupyter_innotater/data.py .

[danlester]

Thank you for letting everyone know!