为什么PngBitmapEncoder类让我的图像颗粒感看？ [英] Why does the PngBitmapEncoder class make my images look grainy?

问题描述

我使用此代码的JPG图像转换成PNG 8
的代码的作品，但图像看起来颗粒感。我确实在Photoshop中导出为PNG 8，它看起来光滑，无颗粒

注意：8位PNG

任何影像大师在那里，可以帮助

我的代码：

 图像镜像文件= Image.FromFile（@C：\Documents和Settings\dvela\My Documents\Downloads\pngtest\Batman01 .JPG）; 
矩形NewSize =新的Rectangle（）; 
 NewSize.Width = 112; 
 NewSize.Height =（NewSize.Width * ImageFile.Height）/ ImageFile.Width; 
 
位图图像=新位图（NewSize.Width，NewSize.Height）; 
 
显卡显卡= Graphics.FromImage（图像）; 
 graphics.CompositingQuality = CompositingQuality.HighQuality; 
 graphics.PixelOffsetMode = PixelOffsetMode.HighQuality; 
 graphics.SmoothingMode = SmoothingMode.HighQuality; 
 
 graphics.DrawImage（镜像文件，NewSize）; 
 
 FormatConvertedBitmap FCB =新FormatConvertedBitmap（System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap（image.GetHbitmap（），IntPtr.Zero，Int32Rect.Empty，BitmapSizeOptions.FromWidthAndHeight（NewSize.Width，NewSize.Height） ），PixelFormats.Indexed8，BitmapPalettes.Halftone256Transparent，0.5）; 
 
 PngBitmapEncoder pngBitmapEncoder =新PngBitmapEncoder（）; 
 pngBitmapEncoder.Interlace = PngInterlaceOption.Off; 
 pngBitmapEncoder.Frames.Add（BitmapFrame.Create（FCB））;使用（流FILESTREAM = File.Open（@ 
 
C：\Documents和Settings\dvela\My Documents\Downloads\pngtest\test.png，FileMode.Create） ）
 {
 pngBitmapEncoder.Save（FILESTREAM）; 
} 
  

解决方案

我发现这个库，做调色板和基于八叉树颜色量化。
http://www.waterwijkers.nl/bip

这篇文章有一个伟大的演示应用程序，显示你如何使用它。
HTTP： //www.aspfree.com/c/a/C-Sharp/Lossless-Image-Resizing-in-C-Sharp/2/

这MSDN文章解释了代码算法之间的差异。
http://msdn.microsoft.com/en-us/library /aa479306.aspx

I'm using this code to convert a jpg image into a png 8. The code works but the image looks grainy. I did an export in Photoshop as png 8 and it looks smoother and no grain.

Note: 8-bit png

Any image gurus out there that can help?

My code:

Image ImageFile = Image.FromFile(@"C:\Documents and Settings\dvela\My Documents\Downloads\pngtest\Batman01.jpg");
Rectangle NewSize = new Rectangle();
NewSize.Width = 112;
NewSize.Height = (NewSize.Width * ImageFile.Height) / ImageFile.Width;

Bitmap image = new Bitmap(NewSize.Width, NewSize.Height);

Graphics graphics = Graphics.FromImage(image);
graphics.CompositingQuality = CompositingQuality.HighQuality;
graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;
graphics.SmoothingMode = SmoothingMode.HighQuality;

graphics.DrawImage(ImageFile, NewSize);

FormatConvertedBitmap fcb = new FormatConvertedBitmap(System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(image.GetHbitmap(), IntPtr.Zero, Int32Rect.Empty, BitmapSizeOptions.FromWidthAndHeight(NewSize.Width, NewSize.Height)), PixelFormats.Indexed8, BitmapPalettes.Halftone256Transparent, 0.5);

PngBitmapEncoder pngBitmapEncoder = new PngBitmapEncoder();
pngBitmapEncoder.Interlace = PngInterlaceOption.Off;
pngBitmapEncoder.Frames.Add(BitmapFrame.Create(fcb));

using (Stream fileStream = File.Open(@"C:\Documents and Settings\dvela\My Documents\Downloads\pngtest\test.png", FileMode.Create))
{
   pngBitmapEncoder.Save(fileStream);
}

解决方案

I found this library that does Palette-based and Octree-based color Quantization. http://www.waterwijkers.nl/bip

This article has a great demo app that shows you how to use it. http://www.aspfree.com/c/a/C-Sharp/Lossless-Image-Resizing-in-C-Sharp/2/

This MSDN article explains the difference between the algorithms with code. http://msdn.microsoft.com/en-us/library/aa479306.aspx

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