https://image.online-convert.com/convert-to-bmp bmp does not display from converted png

[ptorrone]

https://image.online-convert.com/convert-to-bmp bmp does not display from converted png. i used whatever the default settings are on the page, did not make any changes.

attached (files.zip) has the before.png and the after.bmp, the bmp does not display.

files.zip

[oddstr13]

The provided output bitmap is 32bit.

$ python3 test_bmp.py after.bmp 
Color depth: 32
Compression: 3
Colors: 0
Is true color BMP:  True

One of the following imagemagick commands should in theory provide valid bitmaps:

1-bit:

$ convert before.png -compress none -type bilevel 1.bmp
$ python3 test_bmp.py 1.bmp
Color depth: 1
Compression: 0
Colors: 2
Is true color BMP:  False

8-bit:

$ convert before.png -compress none -type palette 8.bmp
$ python3 test_bmp.py 8.bmp
Color depth: 8
Compression: 0
Colors: 256
Is true color BMP:  False

8-bit with RLE compression:

$ convert before.png -compress rle -type palette 8c.bmp
$ python3 test_bmp.py 8c.bmp
Color depth: 8
Compression: 1
Colors: 256
Is true color BMP:  False

Example output
test_bmp.py

See the following for the relevant implementation details:

Adafruit_CircuitPython_ImageLoad/adafruit_imageload/bmp/__init__.py

Lines 52 to 63 in 814bda6

	file.seek(0x1c) # Number of bits per pixel
	color_depth = int.from_bytes(file.read(2), 'little')
	file.seek(0x1e) # Compression type
	compression = int.from_bytes(file.read(2), 'little')
	file.seek(0x2e) # Number of colors in the color palette
	colors = int.from_bytes(file.read(4), 'little')
	if colors == 0 and color_depth >= 16:
	raise NotImplementedError("True color BMP unsupported")
	if compression > 2:
	raise NotImplementedError("bitmask compression unsupported")

In summary: The website you used does not (always?) produce compatible BMP files.

[evaherrada]

Only certain types of bitmaps work. I've linked to a learn guide page in the README where @FoamyGuy explains how to make those bitmaps in gimp

[adipotnis]

I used online-convert.com but I set the image to Monochrome.