wxImage and grayscale BMP files

[vanarieleyen]

I have a problem with BMP files that are in grayscale format.

Where are the pixels in grayscale stored? When I try to access them using for instance getRed() I don't receive the expected result.

When however the BMP file is in 24 bit RGB format and the content is grayscale (each channel has the same value) then I get the correct values.

[doublemax]

How do you load the bitmap and how do you access the pixel value?

wxImage is always be 24bit RGB, so all 3 values should be the same even when loading an 8 Bit bitmap. (Which probably has a palette that contains the grayscale values).

[vanarieleyen]

I use the folowing code to load the bmp file:

Code: Select all

image.LoadFile(filePath, wxBITMAP_TYPE_BMP);

This works fine, when the bmp file is 24 bit (3x8 bit channels) I can read the rgb values, but when the bmp file is in grayscale format it fails.

I use the following to retrieve the pixel values:

Code: Select all

image.GetRed(x,y);

[doublemax]

Can you upload the image anywhere? I can't reproduce this with any bmp i created.

BTW: What platform and wxWidgets version are you using?

[vanarieleyen]

I use widgets vs. 2.8 with windows 8

[doublemax]

I see it now. It seems that the BMP uses a header that wxWidgets doesn't support properly.

https://trac.wxwidgets.org/ticket/18634

[vanarieleyen]

You guys are Amazing!!

I have checked the bug track and saw that it is already fixed. I have immediately applied the fix and compiled it again.

It is now working without any issues.

Thank you for the quick fix!

[doublemax]

Just be warned that i'm not 100% sure if the patch i posted doesn't have any unwanted side-effects under certain conditions. Make sure to follow the ticket so that you know when an "official" fix is committed.

[ONEEYEMAN]

Hi,
Just to add - 2.8 is old.
You need to upgrade wx to at least 3.0 (stable) or 3.1.3 (latest) release.

You will get many more fixes and better library.

Thank you.

[vanarieleyen]

Yes, I understand that it is not an official fix but until now I didn't notice any problems, but of course will follow the ticket.

And no, I made a mistake - I am currently using 3.1.2. Yesterday however I have also tried 3.1.3 but received an error related to wxClientDC. This made me switch back to 3.1.2 - I will wait a while until 3.1.3 is more mature.

Thanks for all the efforts.
Arie