I think we do have possibly two issues actually.

1. It seems that the core release version made it to an "in-between" state where it does have bitmaptools.read_into but it's missing one of the arguments. This is causing the error mentioned above. I built from the current main branch and this error is not raised on that branch:

Adafruit CircuitPython 6.2.0-beta.4-53-ge084a9267-dirty on 2021-03-20; Adafruit Feather RP2040 with rp2040

2. there may also be some issue loading images on the branches that do have this argument.
   Using the current release version of this library with read_into() I get this:
   

using imageload edited not to use read_into()

The image in use is here: https://github.com/adafruit/Adafruit_CircuitPython_ImageLoad/blob/master/examples/images/4bit.bmp

Interestingly some images are okay:

this is one of the icons from the touch deck project. These are the ones I tested the changes with originally.

perhaps there is something specific about the 4bit.bmp image causing trouble. I'll try out a few other images to see if any other have similar things going on.

@kmatch98 when you have a chance to take a look, I'm curious to see if you have ideas about what could be causing the differences in final image shown for this one.

@FoamyGuy I confirmed your issue. I was able to adjust the inputs to _bitmap_readinto to get the shapes to be correct, but some of the colors displayed are all wrong.

I verified that the loaded palette colors exactly the same with both versions. Perhaps the pixel index reads are off by a few bits somewhere? I'm not sure I'll have any time tomorrow to work on this, and anyway we may need to bring jepler into consult.

I added the swap_bytes_in_element = False as shown below and it corrected the shape, but not the colors.

            if _bitmap_readinto:
                _bitmap_readinto(
                    bitmap,
                    file,
                    bits_per_pixel=color_depth,
                    element_size=4,
                    reverse_pixels_in_element=True,
                    swap_bytes_in_element=False,
                    reverse_rows=True,
                )

Just a little bit more information to confirm that some of the bitmap color indexes are off by 8 when using the new readinto function. Interestingly, only certain columns or rows seem to be affected.

Here are the bitmap color indexes when using the previous "standard speed" version:

5 5 5 11 11 6 6 6 14 14 14 3 3 4 4 4 5  
5 5 5 11 11 6 6 6 14 14 14 3 3 4 4 4 5  
5 5 5 11 11 6 6 6 14 14 14 3 3 4 4 4 5  
5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5  
5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5  
5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5  
5 5 5 15 15 1 1 1 9 9 9 0 0 12 12 12 5  
5 5 5 15 15 1 1 1 9 9 9 0 0 12 12 12 5  
5 5 5 15 15 1 1 1 9 9 9 0 0 12 12 12 5  
5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5  
5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5  
5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5  
5 5 5 2 2 10 10 10 8 8 8 13 13 7 7 7 5  
5 5 5 2 2 10 10 10 8 8 8 13 13 7 7 7 5  
5 5 5 2 2 10 10 10 8 8 8 13 13 7 7 7 5  

Here are the bitmap color index values with the new "fast" readinto version:

5 5 5 3 3 6 6 6 6 6 6 3 3 4 4 4 5  
5 5 5 3 3 6 6 6 6 6 6 3 3 4 4 4 5  
5 5 5 3 3 6 6 6 6 6 6 3 3 4 4 4 5  
5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5  
5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5  
5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5  
5 5 5 7 7 1 1 1 1 1 1 0 0 4 4 4 5  
5 5 5 7 7 1 1 1 1 1 1 0 0 4 4 4 5  
5 5 5 7 7 1 1 1 1 1 1 0 0 4 4 4 5  
5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5  
5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5  
5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5  
5 5 5 2 2 2 2 2 0 0 0 5 5 7 7 7 5  
5 5 5 2 2 2 2 2 0 0 0 5 5 7 7 7 5  
5 5 5 2 2 2 2 2 0 0 0 5 5 7 7 7 5 

Ok, I found the issue, was an incorrect bitmask for BMPs with 4-bit indexes, along with the reverse_pixels_in_element=True.

This will require:

• update to bitmaptools.readinto, PR is here: Fix reading 4-bit data circuitpython#4454
• update to this library, PR is here: update readinto input parameters #49

I think the two things above were merged so all should be good to close out this issue.

This was resolved by #48 , #49 , and #4454 in the core.