aaron08

Pls tell me how can i produce a code that will write lets say a line or rectangle in a bitmap file. I understand that i need to have a header file which I already had written. What i do not understand is how can I exactly write to a binary file like a bitmap. I need explanations on how can i work out the problem. thank you.

mike_g

use fopen to open the file. If you want to read as well as write use "r+b" as the second parameter. You can then use fseek to get where you want in the file. If you are writing multibyte data then I think you will also want to cast it to a character array before writing, and you may need to reverse it when reading IIRC.

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Sander

It depends in what format the bitmap file is. Many image formats can be read/written with freely available libraries (libjpeg, libpng, libtiff); other formats are relatively simple and can be decoded and encoded "manually".

I don't understand your remark about a header file.

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aaron08

what i know is that each bitmap file has a file header which contains the size of the image, the bits per pixel etc.

Salem

http://en.wikipedia.org/wiki/BMP_file_format
"draw" your line in a large array of pixels, then write them out the file.

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robwhit

a header file is source code. (stdio.h, stdlib.h, etc)

a file header is data that goes before other data in a file.

Sander

That's what all but the most trivial bitmap file formats have. It depends on the exact file format (i.e., is it a BMP file? GIF, JPEG, TIFF, PNG?) what the precise layout of this file header is. Some file formats are relatively simple and you can read the bitmap data as a simple array of pixels, others have some form of compression and are going to be difficult to parse. Fortunately, like I said, there are often libraries available; or perhaps your OS has built-in functions to deal with these files.

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mike_g

Yeah, but GIF, JPEG, TIFF and PNG are not bitmaps. Bitmaps should have "BM" (edit: in ASCII) as the first two bytes in the header. Palleted bitmaps can complicate things tho.

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Sander

That depends on what your definition of "bitmap" is. If you mean "the contents of a BMP file" then you are right. But you could also mean "a rectangular array of pixel values" (as opposed to a "vector image"). It wasn't clear to me from the original poster what he meant.