Many image processing algorithms are defined for grayscale (or else monochromatic) images.



Task

Extend the data storage type defined on this page to support grayscale images.

Define two operations, one to convert a color image to a grayscale image and one for the backward conversion.

To get luminance of a color use the formula recommended by CIE:

 L  =  0.2126 × R   +   0.7152 × G   +   0.0722 × B 

When using floating-point arithmetic make sure that rounding errors would not cause run-time problems or else distorted results when calculated luminance is stored as an unsigned integer.




DIM colored = ".\LenaClr.bmp", grayscale = ".\LenaGry.bmp"
DIM head, tail, r, g, b, l, ptr, blobsize = 54 ' sizeof BMP file headers
 
FILEGET(FILEOPEN(colored, BINARY), FILELEN(colored)): FILECLOSE(FILEOPEN) ' load buffer
head = @FILEGET + blobsize: tail = @FILEGET + FILELEN ' set loop bounds
 
FOR ptr = head TO tail STEP 3 ' transform color triplets
	b = PEEK(ptr + 0, 1) ' read Windows colors stored in BGR order
	g = PEEK(ptr + 1, 1)
	r = PEEK(ptr + 2, 1)
	l = 0.2126 * r + 0.7152 * g + 0.0722 * b ' derive luminance
	SETMEM(FILEGET, RGB(l, l, l), ptr - head + blobsize, 3) ' write grayscale
NEXT
 
FILEPUT(FILEOPEN(grayscale, BINARY_NEW), FILEGET): FILECLOSE(FILEOPEN) ' save buffer