[racket] processing images...

From: geb a (geb_a at yahoo.com)
Date: Mon Apr 11 13:16:30 EDT 2011

Hello all,  

I'm having some trouble processing a block of pixels from an image. I want to grab some portion of image, do something to it, and save it to a file.  In this example, I grab a portion of an image and save it to a file but the image in the file is corrupted.  Evidently I'm doing something wrong.  I've spent a number of hours trying to figure it out, but I'm blind to the problem.  I would be very grateful for any help someone can give me.


Dan Anderson

#lang racket/gui
; define the portion of the image I want to process
(define x 0)
(define y 0)
(define w 10)
(define h 10)

(define bm (make-object bitmap% "4colors.jpg"))

(define pixels (make-bytes (* w h 4) 0)) ;each pixel has four numbers 
(send bm get-argb-pixels x y w h pixels true) ; get the block of pixels

pixels ;check that there is information in pixels 
;make a new bitmap of the section
(define nbm (make-object bitmap% pixels w h))
(send nbm save-file "test.png" 'png)

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