Lazarus

Programming => Graphics and Multimedia => Graphics => Topic started by: Igor Kokarev on September 23, 2021, 01:52:40 pm

Title: TFPWriterPNG compression ratio problem
Post by: Igor Kokarev on September 23, 2021, 01:52:40 pm

Hi,

I use TFPWriterPNG to save a PNG image from TFPCustomImage with max compression.

Even with clMax compression a resulting PNG in 1.3x larger than the same PNG image saved in Photoshop or another editor.

Yes, I know that TFPCustomImage works at 64-bit per pixel, and I set TFPWriterPNG.WordSized:=False to convert it to 32-bit pixel format.

My project doesn't use LCL and I can use only pure FPC code.

FPC 3.2.0 / Lazarus 2.0.10

Code: Pascal  [Select][+][-]

1. program PngSaveTest;
2.  
3. {$APPTYPE CONSOLE}
4.  
5. {$ifdef fpc}{$mode Delphi}{$endif}
6.  
7. uses
8.   Classes, FPImage, FPWritePNG, FPReadPNG, ZStream;
9.  
10. procedure SavePNG;
11. type TReadKlas = class of TFPCustomImageReader;
12. var
13.   image: TFPCustomImage;
14.   Ireader: TFPCustomImageReader;
15.   IWriter: TFPWriterPNG;
16.   Reader : TReadKlas;
17. begin
18.   Image := TFPMemoryImage.Create(8, 8);
19.   reader:=TFPReaderPNG;
20.   IReader:=Reader.Create;
21.   Image.LoadFromFile('Src.png',IReader);
22.   iReader.Free;
23.  
24.   IWriter := TFPWriterPNG.Create;
25.   IWriter.UseAlpha:=False;
26.   IWriter.WordSized:=False;
27.   IWRiter.CompressionLevel:=clMax;
28.   Image.SaveToFile('Dst.png',IWriter);
29.   IWriter.Free;
30.  
31.   image.Free;
32. end;
33.  
34. begin
35.   SavePng;
36. end.

Title: Re: TFPWriterPNG compression ratio problem
Post by: marcov on September 23, 2021, 02:15:58 pm

png doesn't just have Z lib compression, but also configurable filters before hand.  Some editors that have no time constraints on save try multiple and then save the smallest.

Title: Re: TFPWriterPNG compression ratio problem
Post by: Igor Kokarev on September 24, 2021, 02:46:46 pm

Thanks, I've understood.