24 bpp BMP to Negative

Simple haskell script that inverts (creates a negative of) a given .bmp image. The original miage must be:

1. 24 bpp pixel size
2. Uncompressed

title	original	negative
bmp_24
color wheel
snail
blackbuck
marbles

Example images can be found in /images directory. /images/unsupported images contain examples of unsupported .bmp images.

Executable Guide

• Install the executable using cabal install
• Run the exectuable using bmp-negative {PATH_TO_BMP_IMAGE}
  • -h flag for help message
• Image will be generated in the same directory as the original image.

How it Works

• Script imports the .bmp image as a ByteString and converts is to a [Byte] or byte array.
• Split the byte array as (Header,PixelData).
  • Initially, the header data is parsed. Check whether application accepts the given .bmp.
  • Parse the PixelData.
    • We can consider it as an array of Rows.
    • Each Row is a byte array of RGB color bytes and Padding bytes.
    • The number of Padding bytes is rowSize - 3 * width, where rowSize = div (width * 24 + 31) 32 * 4
  • Relevent type alias' here:

    type BmpImage   = (Header,PixelData)
    type Header     = [Byte]
    type PixelData  = [Row]
    type Row        = (RGB,Padding)
    type RGB        = [Byte]
    type Padding    = [Byte]
    

• Invert the image. It's a simple operation of 255 - b, where b is an RGB color byte.
• Write the new BmpImage as a new .bmp.