Reading a BMP into memory using the correct structures

I'm currently doing a steganography project (for myself). I have done a bit of code already but after thinking about it, I know there are better ways of doing what I want.

Also - this is my first time using dynamic memory allocation and binary file I/O.

Here is my code to hide a text file within a BMP image: Link to code

Also note that I'm not using the LSB to store the message in this code, but rather replacing the alpha byte, assuming its a 32 bit per pixel (bbp) image. Which is another reason why this won't be very flexible if there are 1, 4, 8, 16, 24 bpp in the image. For example if it were 24 bbp, the alpha channel will be 6 bits, not 1 byte.

My question is what is the best way to read the entire BMP into memory using structures?

This is how I see it:

• Read BITMAPFILEHEADER
• Read BITMAPINFOHEADER
• Read ColorTable (if there is one)
• Read PixelArray

I know how I to read in the two headers, but the ColorTable is confusing me, I don't know what size the ColorTable is, or if there is one in an image at all.

Also, after the PixelArray, Wikipedia says that there could be an ICC Color Profile, how do I know one exists? Link to BMP File Format (Wikip开发者_StackOverflowedia)

Another thing, since I need to know the header info in order to know where the PixelArray starts, I would need to make multiple reads like I showed above, right?

Sorry for all the questions in one, but I'm really unsure at the moment on what to do.

The size of the color table is determined by bV5ClrUsed.

An ICC color profile is present in the file only if bV5CSType == PROFILE_EMBEDDED.

The documentation here provides all that information.

Then, 24-bit color means 8 red, 8 green, 8 blue, 0 alpha. You'd have to convert that to 32-bit RGBA in order to have any alpha channel at all.

Finally, the alpha channel DOES affect the display of the image, so you can't use it freely for steganography. You really are better off using the least significant bits of all channels (and maybe not from all pixels).