ImageIO.imwrite “ValueError: Could not find a format to write the specified file in single-image mode” for

Question

I'm trying to save images that were processed (started as Raw Image, want to save it back to Raw/dng/nef) This given ndarray is just -1,0,1 where certain pixels exceeded a threshold

I'm having trouble grasping what the issue is here:

imageio.imsave('images/imagesTest', image.Red.ZthreshMap)

Given this I get this error back:

File "C:\Users\E\--\PycharmProjects\lib\site-packages\imageio\core\functions.py", line 303, in imwrite
    writer = get_writer(uri, format, "i", **kwargs)
  File "C:\Users\E\--\PycharmProjects\lib\site-packages\imageio\core\functions.py", line 227, in get_writer
    "Could not find a format to write the specified file in %s mode" % modename
ValueError: Could not find a format to write the specified file in single-image mode

I confirmed just in case that I'm supplying the function with the right data type:

<class 'numpy.ndarray'>

Is what the type is so that should work fine.

So I tried this where I specify the file type:

imageio.imsave('images/imagesTest.dng', image.Red.ZthreshMap, '.dng')

File "C:\Users\E\--\PycharmProjects\lib\site-packages\imageio\plugins\freeimage.py", line 127, in _append_data
    self._bm.allocate(im)
  File "C:\Users\E\--\PycharmProjects\lib\site-packages\imageio\plugins\_freeimage.py", line 825, in allocate
    raise ValueError("Cannot write arrays of given type and shape.")
ValueError: Cannot write arrays of given type and shape.

Which is strange because I double checked the shape and:

print(image.Red.ZthreshMap.shape)

ends up resulting in (1434, 2160)

Any recommendations?

Answer 1

If you clarify better what you are trying to do, it'll be easier to help you. Why are you "shooting for no compression" ? If your file consists purely of values -1 , 0 and 1 it should compress very well - losslessly which is surely advantageous.

At the moment, there are likely 2 issues:

• you haven't specified a file extension so imageio doesn't know if you want to save a PNG, TIFF or JPEG

• some of your values are -1 , and few image formats can save negative numbers because they normally record the brightness above black, so a negative number would be backer than black and as that doesn't happen, image formats don't bother allowing valuable space for negative numbers.