TFPWriterPNG compression ratio problem
lazarus / 39-Graphics

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Igor · 2021-09-23 11:52

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][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
PngSaveTest; {$APPTYPE CONSOLE} {$ifdef fpc}{$mode
Delphi}{$endif} uses  Classes, FPImage, FPWritePNG, FPReadPNG,
ZStream; procedure SavePNG;type TReadKlas = class of
TFPCustomImageReader;var  image: TFPCustomImage;  Ireader:
TFPCustomImageReader;  IWriter: TFPWriterPNG;  Reader :
TReadKlas;begin  Image := TFPMemoryImage.Create(8, 8); 
reader:=TFPReaderPNG;  IReader:=Reader.Create; 
Image.LoadFromFile('Src.png',IReader);  iReader.Free;   IWriter :=
TFPWriterPNG.Create;  IWriter.UseAlpha:=False; 
IWriter.WordSized:=False;  IWRiter.CompressionLevel:=clMax; 
Image.SaveToFile('Dst.png',IWriter);  IWriter.Free;  
image.Free;end; begin  SavePng;end.

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marcov · 2021-09-23 12:15

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.

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Igor · 2021-09-24 12:46

Thanks, I've understood.