Mask out white color from PNG or GIF image, blit it to canvas using any color

Source is either PNG or GIF where the pixels that should be "colorized" are white. Background can be either black or transparent, whichever is easiest.

Now I'd like to cut out a rectangular part of the source, and AND it with the palette color (gif) or RGB color (png) of the "brush", to "s开发者_开发百科tamp" it out on a TImage/TCanvas with that color.

Probably one of those lazy questions where RTFM would do. But if you have a nice solution please share :)

I tried Daud's PNGImage lib, but I can't even get it loading the source image. Is there a trick to using it?

The solution needs to work on D7 and up, XP and up.

do i understand you want to change the white color with some other color? if that is so i think you should check the image pixel by pixel and check what color is the pixel and change it if is white.

thats how you can loop through image

var
  iX  : Integer;
  Line: PByteArray;
...
  Line := Image1.ScanLine[0]; // We are scanning the first line
  iX := 0;
  // We can't use the 'for' loop because iX could not be modified from
  // within the loop
  repeat
    Line[iX]     := Line[iX] - $F; // Red value
    Line[iX + 1] := Line[iX] - $F; // Green value
    Line[iX + 2] := Line[iX] - $F; // Blue value
    Inc(iX, 3); // Move to next pixel
  until iX > (Image1.Width - 1) * 3;

Here's code that show how to reads the Red and Blue values and switched them.

var
  btTemp: Byte; // Used to swap colors
  iY, iX: Integer;
  Line  : PByteArray;
...
  for iY := 0 to Image1.Height - 1 do begin
    Line := Image1.ScanLine[iY]; // Read the current line
    repeat
      btSwap       := Line[iX];     // Save red value
      Line[iX]     := Line[iX + 2]; // Switch red with blue
      Line[iX + 2] := btSwap;       // Switch blue with previously saved red
      // Line[iX + 1] - Green value, not used in example
      Inc(iX, 3);
    until iX > (Image1.Width - 1) * 3;
  end;
  Image1.Invalidate; // Redraw bitmap after everything's done

but this is for bitmap image only.

if this is useful try to convert your image to bitmap and from then manipulate it.