Computing BITMAPINFOHEADER biCompression value for monochrome BMP

Question

Hi all,

Hopefully someone has an answer, and it's not TOO complex. I'm working on a C++ dll (no C# or .Net, fully static DLL).

Anyhow, its woring on buildin monochrome bitmaps. I have all of it working EXCEPT the resolution. I get the Device Context, Get Compatible Device Context, build bitmap, draw what I need to (as black/white), and can save. All this works fine. However, I can't figure out how to set the resolution of the bitmap.

While doing some testing from another utility under C#, I can create a bitmap and set the resolution. In doing so, I ran a routine to generate the same file content with a parameter from 1 to 300 for the resolution. Each image came out exactly the same EXCEPT for the values in the "biCompression" DWORD property. The default is the screen resolution of 96x96, but need to obviously change for printers of 300x300, and even some at 203x203 resolution.

TIA for the help

Answer 1

Are you absolutely sure? The description of the behavior you observe sounds fishy to me and I would suspect the code that you're using to write your bitmaps or your code that reads them back in.

Answer 2

Are you sure you don't want to set biXPelsPerMeter and biYPelsPerMeter? Those two fields tell you how many pixels per meter in X and Y, which you can use to set the DPI. biCompression only deals with the compression type of the bitmap, e.g., RLE, JPG, PNG, etc.

Answer 3

Thanks for input, but I'll look into the biXPelsPerMeter an biYPels... too. I'll double check the format, and what was set... if so, you may have hit it with a second set of eyes (minds) on my issue.

Thanks