Writing bitmap file in c

I might create a small Visual Studio project using this bitmap as an example. Vil 27 August I have found this quite useful. Andy 28 August Thanks for the very useful feedback! Kind regards Andy. Terry 11 September Claude 24 February Lovely stuff.

Code duly updated. Thanks for the feedback! Davidson 12 October I try compiling but receive the following errors. M 19 March First header bitmap file header tells that this binary file is a bitmap file. The next header bitmap info header contains additional meta-data about the image. For bitmap file header 14 bytes we need to create the following data structure:.

The first two bytes 'B' and 'M' are unique to the bitmap file format there still are different versions of it check bitmap format specification. The next four bytes contain total size of the bitmap file in bytes. The last field of bitmap file header contains the offset to the pixel data of the image from the start of the file. The bitmap file has various types of info header, but the most common one is the 40 byte Bitmap Info Header, so we need to write it down in the following data structure:.

The height of bitmap file can also be negative you may have noticed the signed integers. When height is negative the first pixel in file is drawn at top left of the image. However the standard for bitmap files is to use positive height and the first pixel in file is drawn at the bottom left of the image followed by other pixels.

The bitmap file may also contain a color table but it is not mandatory in a 24 bit bitmap file, so we will not be creating one in this example.

As I'll be creating a mono color bitmap image all pixels have same value , I'm creating an additional struct for the pixel:. Each channel in a pixel must be an unsigned integer of 1 byte for a 24 bit bitmap file. Where specifies maximum color intensity and 0 specifies absence of the color. A struct may have padding additional bytes added by the compiler for optimizing performance.

Hence sizeof is not going to return accurate value. So I have manually specified the size of each struct in ofstream::write method. Here is the code tested on linux. Balamurugan A Balamurugan A 1, 1 1 gold badge 16 16 silver badges 19 19 bronze badges. This assumes your native endianness is the same as Windows' the originator of the BMP file format. Definitely going to try that tomorrow!

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Bitmap information header: contains the properties of the pixel data. Data: the actual pixel data. Reading a BMP file To extract the pixel information you could decide to read every field from the header based on the table above. Our example image would look like this: This is because the image is stored bottom-up and the rows contain padding bytes to make their size a multiple of 4.