Image processing algorithm (6)

Vi. Contrast
Scan the image, find the maximum and minimum values of the image brightness, map Max to smaller values such as 255 or 250, and map min to smaller values such as 0 or 5, and re-calculate the brightness of each point.

1 Public   Static   Bool Contrast (Bitmap B, Int Lavel)
2 {
3 If (Lavel <   - 100 ) Return   False ;
4 If (Lavel > 255 ) Return   False ;
5
6 Bitmapdata bmdata = B. lockbits ( New Rectangle ( 0 , 0 , B. Width, B. Height ),
7 Imagelockmode. readwrite, pixelformat. format24bpprgb );
8
9 Double Pixel =   0 , Contrast = ( 100.0   + Lavel) /   100.0 ;
10 Contrast * = Contrast;
11
12 Int Stride = Bmdata. stride;
13 System. intptr scan0 = Bmdata. scan0;
14
15 Unsafe
16 {
17 Byte   * P = ( Byte   * )( Void   * ) Scan0;
18 Int Red, green, blue;
19 Int Noffset = Stride - B. Width * 3 ;
20
21 For ( Int Y =   0 ; Y < B. height; ++ Y)
22 {
23 For ( Int X =   0 ; X < B. width; ++ X)
24 {
25 Blue = P [ 0 ];
26 Green = P [ 1 ];
27 Red = P [ 2 ];
28
29 Pixel = Blue /   255.0 ;
30 Pixel -=   0.5 ;
31 Pixel * = Contrast;
32 Pixel + =   0.5 ;
33 Pixel * =   255 ;
34 If (Pixel <   0 ) Pixel =   0 ;
35 If (Pixel >   255 ) Pixel =   255 ;
36 P [ 0 ] = ( Byte ) Pixel;
37
38 Pixel = Green /   255.0 ;
39 Pixel -=   0.5 ;
40 Pixel * = Contrast;
41 Pixel + =   0.5 ;
42 Pixel * =   255 ;
43 If (Pixel <   0 ) Pixel =   0 ;
44 If (Pixel >   255 ) Pixel =   255 ;
45 P [ 1 ] = ( Byte ) Pixel;
46  
47 Pixel = Red /   255.0 ;
48 Pixel -=   0.5 ;
49 Pixel * = Contrast;
50 Pixel + =   0.5 ;
51 Pixel * =   255 ;
52 If (Pixel <   0 ) Pixel =   0 ;
53 If (Pixel >   255 ) Pixel =   255 ;
54 P [ 2 ] = ( Byte ) Pixel;
55
56 P + =   3 ;
57 }
58 P + = Noffset;
59 }
60 }
61 B. unlockbits (bmdata );
62 Return   True ;
63 }