Function Reference


Generates a checksum for a region of pixels.

PixelChecksum ( left, top, right, bottom [, step = 1 [, hwnd [, mode = 0]]] )


left left coordinate of rectangle.
top top coordinate of rectangle.
right right coordinate of rectangle.
bottom bottom coordinate of rectangle.
step [optional] Instead of checksumming each pixel use a value larger than 1 to skip pixels (for speed). E.g. A value of 2 will only check every other pixel. Default is 1. It is not recommended to use a step value greater than 1.
hwnd [optional] Window handle to be used. Default is the desktop window.
mode [optional] default 0 ADLER checksum, 1 CRC32 Checksum.

Return Value

Success: the checksum value of the region.
Failure: 0.


A checksum only allows you to see if "something" has changed in a region - it does not tell you exactly what has changed.

CRC32 checksum is a little slower than ADLDER but detects better pixel variation.


PixelCoordMode (Option), PixelGetColor, PixelSearch


#include <MsgBoxConstants.au3>

; Wait until something changes in the region 0,0 to 50,50

; Get initial checksum
Local $iCheckSum = PixelChecksum(0, 0, 50, 50)

; Wait for the region to change, the region is checked every 100ms to reduce CPU load
While $iCheckSum = PixelChecksum(0, 0, 50, 50)

MsgBox($MB_SYSTEMMODAL, "", "Something in the region has changed!")