TPNGImage help

PNG Delphi

Converting to partial transparency


The PNG Delphi latest release provides a method to generate transparency data for the current image when its not avaliable, this method is CreateAlpha. It generates alpha information:
  • When the image color type is COLOR_RGB or COLOR_GRAYSCALE it converts to COLOR_RGBALPHA and COLOR_GRAYSCALEALPHA and makes the AlphaScanline property avaliable.
  • For COLOR_PALETTE color type, it generates a tRNS chunk which may be acessed using Chunks.ItemFromClass.

If the image already contains alpha information, the method don't do nothing, so its always safe to call it. Also, it initialize the transparency image so the image is fully opaque for booth COLOR_PALETTE and COLOR_RGB/COLOR_GRAYSCALE modes.

To access the transparency information when the image is COLOR_RGB/COLOR_GRAYSCALE use the first way, and for COLOR_PALETTE use the second way.