YuPng brings libpng to Delphi, with its complete API of functions, types, and constants. libpng is the official PNG reference library. libpng supports almost all PNG features, is extensible, and extensively tested. YuPng links libpng statically, no DLLs needed.

The TYuPngImage class desecends from TGraphic. It loads and draws PNG images with support for embedded ICC color profile conversion, gamma correction, and chromaticities. Features:

• ICC (International Color Consortium) profile 2.0 and 4.4 color management based on Little CMS.
• All allowed PNG color types supported: RGB color, palette, and grayscale with 1, 2, 4, 8, and 16-bit bit depths, respectively.
• Alpha transparency.
• Progress callback with correct percentages, including interlaced PNG images.

Of course, all required code for TYuPngImage is statically linked into executable binaries and needs no DLLs.

Next to TYuPngImage, the complete libpng API is available for custom implementations to read and write, modify and create PNG images.

Demo projects, including a YuPng Image Viewer with thumbnails preview are included in the download.

YuPng came into being to make up for the deficiencies and bugs of Delphi's TPngImage, for a demonstration of the most notorious ones see below.

All examples were created by Delphi 11.2 Alexandria, the most recent Delphi at the time of this writing. The left and right images are drawn on a checker board pattern to show their transparent pixels. The center image points out pixel differences with a red color overlay.

• Embedded ICC color profiles go unnoticed in TPngImage. TYuPngImage reads the iCCP chunk and applies the proper color conversions. In this example, red and blue are swapped.
  

• In this example, failure to apply ICC color profiles leads to negative rendering of grayscale images. The correct gradient is white on the left and black on the right.
  

• Primary chromaticities and white point are not handled in TPngImage. TYuPngImage reads the cHRM chunk and applies the red, green, and blue chromaticities and the referenced white point. In this example, red and green are swapped.
  

• 2-bit grayscale images show wrong colors in TPngImage. The differences are in stainted shades of gray, whereas the lightest color should be a clean white.
  

• 2-bit grayscale can have 7 colors in TPngImage, where only 4 colors are possible. The artistic diff-pattern hints at an algorithmic problem. TYuPngImage is less imaginative and sticks the correct 4 colors.
  

• Transparency ignored for 16-bit grayscale in TPngImage so the checker board does not shine through.
  

• Transparency ignored for 16-bit color as well in TPngImage.
  

• Access Violation and memory leak on invalid IHDR data in TPngImage. Older Delphis are more prone to AV than newer ones, but even the current Delphi 11.2 Alexandria is affected. TYuPngImage issues a proper error message and does not leak memory, in all Delphi versions.
  

{ Add the YuPngImage unit once to any uses clause 
  to register TYuPngImage as the PNG handler. }
uses
  Graphics, // For TPicture.
  YuPngImage; // Registers TYuPngImage.
 
procedure LoadPng;
var
  pic: TPicture;
begin
  pic := TPicture.Create;
  try
    pic.LoadFromFile('image.png');
    { Add code here to do something with the picture. }
  finally
    pic.Free;
  end;
end;

YuPng development uncovered a problem in Little CMS:

• Little CMS wrong black point compensation in case of matrix-shaper with inverted curves.