Cimage access pixel and pixel Operation Summary

Msdn code

1. Colorref pixel;
2. Int Maxy = imgoriginal. getheight (), Maxx = imgoriginal. getwidth ();
3. Byte R, G, B, AVG;
4. For (INT y = 0; y <Maxy; y ++ ){
5. For (INT x = 0; x <Maxx; X ++ ){
6. Pixel = imgoriginal. getpixel (x, y );
7. R = getrvalue (pixel );
8. G = getgvalue (pixel );
9. B = getbvalue (pixel );
10. AVG = (R + G + B)/3;
11. Imgoriginal. setpixelrgb (X, Y, AVG, AVG, avg );
12. }}

This method is very inefficient, because every call to getpixel contains the program's stack entry and exit. Therefore, in the face of a large amount of data to be processed, the method of direct access to the memory address is used.

1. Byte * prealdata;
2. Prealdata = (byte *) imgoriginal. getbits ();
3. Int Pit = imgoriginal. getpitch ();
4. Int bitcount = imgoriginal. getbpp ()/8;
5. For (INT y = 0; y <Maxy; y ++ ){
6. For (INT x = 0; x <Maxx; X ++ ){
7. Int grayval = (INT) (* (prealdata + pit * Y + x * bitcount) * 0.3
8. + (INT) (* (prealdata + pit * Y + x * bitcount + 1) * 0.59
9. + (INT) (* (prealdata + pit * Y + x * bitcount + 2) * 0.11;
10. * (Prealdata + pit * Y + x * bitcount) = grayval;
11. * (Prealdata + pit * Y + x * bitcount + 1) = grayval;
12. * (Prealdata + pit * Y + x * bitcount + 2) = grayval;
13. // If it is an 8-bit grayscale image, read a byte bit directly as the grayscale value.
14. // For 24-bit RGB Images, read pixaddr, pixaddr + 1 in sequence, and pixaddr + 2 is the B, G, and r component values.
15. }}

Two methods are used to process the same image (3264*2448 pixels). The former takes 1 minute, and the latter takes about 1 second.

Therefore, the latter is at least 60 times faster than the former.

 

Another method for direct access to the memory address:

Int I, j, temp; int pixel [4]; int width = yuantu. getwidth (); int Height = yuantu. getheight (); int widthbytes = yuantu. getpitch (); bianyuantu. create (width, height, yuantu. getbpp (); If (yuantu. isindexed () {yuantu. getcolortable (0,256, colortable); bianyuantu. setcolortable (0,256, colortable);} byte * pyuantudata = (byte *) yuantu. getbits (); byte * pbianyuantudata = (byte *) bianyuantu. getbits (); For (j = 0; j 
　　
How to convert a color image to a grayscale image
// Convert a true color image to a grayscale image and directly modify the pixel value
 

 

 
  
Void pixelschangedtogray (cimage * pimage)
 
  
{
 
  
Int nbyte, J, I, nwidth, nheight, nbytesperpixel;
 
  
Byte * ppixelline, cnewpixelvalue;
 
  
Nwidth = pimage-> getwidth (); nheight = pimage-> getheight ();
 
  
Nbytesperpixel = pimage-> getbpp ()/8;
 
  
For (I = 0; I <nheight; I ++ ){
 
  
Ppixelline = (byte *) pimage-> getpixeladdress (0, I );
 
  
Nbyte = 0;
 
  
For (j = 0; j <nwidth; j ++) {cnewpixelvalue = (byte) (0.11 * ppixelline [nbyte]
 
  
+ 0.59 * ppixelline [nbyte + 1]
 
  
+ 0.30 * ppixelline [nbyte + 2]);
 
  
Ppixelline [nbyte] = ppixelline [nbyte + 1] = ppixelline [nbyte + 2]
 
  
= Cnewpixelvalue;
 
  
Nbyte + = nbytesperpixel;
 
  
}
 
  
}
 
  
}

 
 
// Changes a non-real color image to a grayscale image and modifies the color palette information.

 

 
  
Void palettechangedtogray (cimage * pimage)
 
  
{
 
  
Rgbquad colortabs [256];
 
  
Int I, ncolortableentries, nnewgraycolor;
 
  
Ncolortableentries = pimage-> getmaxcolortableentries ();
 
  
Pimage-> getcolortable (0, ncolortableentries, colortabs );
 
  
For (I = 0; I <ncolortableentries; I ++ ){
 
  
Nnewgraycolor = (INT) (0.11 * colortabs [I]. rgbblue
 
  
+ 0.59 * colortabs [I]. rgbgreen
 
  
+ 0.30 * colortabs [I]. rgbred );
 
  
Colortabs [I]. rgbblue = (byte) nnewgraycolor;
 
  
Colortabs [I]. rgbgreen = (byte) nnewgraycolor;
 
  
Colortabs [I]. rgbred = (byte) nnewgraycolor;
 
  
}
 
  
Pimage-> setcolortable (0, ncolortableentries, colortabs );
 
  
}

 
Cimage access pixel and pixel Operation Summary