BMP files with alpha channel are read with incorrect channel order

[lassoan]

When a 32-bit ARGB BMP file is loaded using ITK, the colors are all mixed up.

Description

BMP files with transparency are stored with ARGB channel order. It seems that ITK assumes RGBA order.

Steps to Reproduce

Load this image using ITK: https://1drv.ms/u/s!Arm_AFxB9yqHxcpbEw34sbS-h1pjkA?e=cf39o8

img = sitk.ReadImage('15-14-49.bmp')
myshow(img)  # incorrect

nda = sitk.GetArrayFromImage(img)
img2=sitk.GetImageFromArray(nda[:,:,[1,2,3,0]])
myshow(img2)  # correct

Expected behavior

Colors should appear correctly in an application, regardless of what file format is loaded from (png, jpg, bmp, ...)

Actual behavior

Colors are not correct if BMP format is used (if transparency is stored with the image).

Reproducibility

100%

Versions

v5.2.0

Environment

all (Windows and Linux tested)

Additional Information

See original user report at https://discourse.slicer.org/t/grey-level-image-looking-blue-or-other-color/18095/3

[dzenanz]

It turns out BMP files use BGR and BGRA order. ITK assumed ABGR instead. #2596 fixes that.

@leodemachado can you confirm? I guess this will need to be integrated into Slicer first 😄