prankapo / bitmap-writer

A simple bitmap image writer in C.

BMP Image Writing Library

Here is a simple C code using which one can write a BMP image file. This library is made up by bmp.h and bmp.c. bmp.h contains the defintions of the following structures:

1. BMP_HEADER: Contains the members which make up a typical BMP file header (BITMAPFILEHEADER in this figure).
2. DIB_HEADER: Contains members which make up the Device Independent Bitmap (DIB) header. There are many DIB header formats for different purposes. BITMAPINFOHEADER is used in this library because of its simplicity and widespread usage.
3. Image: Contains variable bmp and dib of type struct BMP_HEADER and struct DIB_HEADER, respectively. Along with these, an unsigned 8-bit integer pointer, pixel_data, and a 16-bit unsigned integer, padding, are also members of Image.
   padding contains the number of null bytes which need to be appended to each row of raw pixel data to make the length of the row divisible by 4. For example, if the width of the image is 3 pixels, then the value of padding will be 3. This implies that with 3 bits per pixel, we need a padding of 3 bytes to make the row divisible by 4.
   pixel_data is a pointer to an array of bytes. Most of these bytes store the value of RBG color components of every pixel in an image, whereas some of these bytes are just for padding the row to make it a legitimate BMP file row.

To use this library, you need to compile bmp.c using a compiler supporting C99 and above (You cannot use C89 because of the inline keyword used in trib function's definition in bmp.c). In you main project file, you need to include bmp.h as is shown below (make sure the the path to the header is correctly mentioned while including it and during compilation):

#include "bmp.h"

To write an image, you need the following things:

1. A file pointer pointing to a file opened in binary-write (wb) mode.
2. Height and width of your image.
3. Horizontal and vertical resolution of your image.

You have to then fill and write image headers to file using fill_img_headers() and write_img_headers_to_fil(), respectively.
Once the headers have been written, you can now set the value of individual pixels of you image using set_pixel(), and finally write them in one shot using write_pixels_to_file(). If you wish to write all the pixels in the image again, use fseek() as is shown while writing img3.bmp in write_img.c.
write_img.c contains 5 examples, which I feel sufficiently informs the user of the application and scope of this library. Example 4 and 5 produce patterns which somewhat resemble the interference pattern in a double slit experiment and the patterns produced on a CRO, respectively.