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How do I convert 24bpp bitmap images to 32bpp color and 16 bpp grayscale bitmap images?

Posted on 2015-01-22
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Last Modified: 2015-01-22
Hi:

I've got an app that does bitmap analysis.
Currently we've been working against 24bpp bitmaps.

We need to test our code against 32bpp and 16bpp grayscale bitmaps.
We've got a bunch of 24bpp bitmaps as part of our test images.
Ideally, we'd like to use the same images but convert them to the desired
formats.

1) What is the best way to accomplish this?

2) Are there any drawing tools (either desktop or web based) which I could use?
    (This would be the preferred method.)

3) Our app is a 32 bit unmanaged windows app. It's written in C++ and utilizes the
openCV, boost and GDI+ libraries. How would I do this programmatically?
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Question by:jxbma
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jkr earned 500 total points
ID: 40564656
Gimp (http://www.gimp.org/) can do that, and it's GPL. Just use 'File|Export as...', select Windows Bitmap and choose the bit depth in the dialog that follows.

Regarding how to do that in code, I couldn't find an example on MSDN, but this discussion: https://social.msdn.microsoft.com/Forums/vstudio/en-US/08d03bbb-e535-4b53-a74e-3b021130fc82/gdiimage-how-to-change-pixelformat-to-pixelformat24bpprgb?forum=vcgeneral

Or, in short:
Image* image = new Image(L"temp.bmp"); // 24bit image

Bitmap *dest = new Bitmap(image->GetWidth(), image->GetHeight(), PixelFormat32bppRGB);

//create a graphics from the image
Graphics *g = Graphics::FromImage(dest);

//draw the 32bit per pixel image into the 32 bit per pixel image
g->DrawImage(image, Point(0, 0));

delete image; // source

//now save the 24 bit per pixel to disk
CLSID m_clsidGdiplusBmpEncoder;
GetEncoderClsid( L"image/bmp", &m_clsidGdiplusBmpEncoder );
dest->Save( L"temp2.bmp", &m_clsidGdiplusBmpEncoder, NULL );

delete dest;
delete g; 

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(Source: Internet :-/)
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