TPNGImage help

PNG Delphi

Components > TPNGObject > Properties > AlphaScanline


Provides pointer to direct access to alpha information

property
AlphaScanline[const Index: Integer]: pByteArray;

Description

Some kind of Portable Network Images also provides transparency information. This allows the images to be draw on the screen with transparent parts by blending the foreground against the background using the value provided.
Scanline property provides direct access to image contents and AlphaScanline provides direct access to the image transparency.

It's important to know that only when ColorType is COLOR_RGBALPHA or COLOR_GRAYSCALEALPHA AlphaScanline is valid. For other color types, this property will return nil.

The data in the pointer received will be always an array of bytes with the same size as the image width meaning that each byte represents the transparency for the correspondent position starting from 0 (totally transparent) to 255 (opaque).