Scaling a System Drawing Bitmap to a given size while maintaining aspect ratio

Question

I want to scale a System Drawing Bitmap to at least less than some fixed width and height  This is to generate thumbnails for an image gallery on a website  so I want to keep the aspect ratio the same   I have some across quite a few solutions but none seem to really do what I need  they revolve around scaling based on keeping the width or the height the same but not changing both   An example   If I have a 4272 by 2848 image and I want to scale it to a size of 1024 by 768  then the resulting image should be 1024 by 683 and padded  with a black border  to 1024 by 768   How can I do this with images larger than the required size and smaller than the require sized and also pad images which don t come out to the exact size I need once scaled

User · Answer

The bitmap constructor has resizing built in.

Bitmap original = (Bitmap)Image.FromFile("DSC_0002.jpg");
Bitmap resized = new Bitmap(original,new Size(original.Width/4,original.Height/4));
resized.Save("DSC_0002_thumb.jpg");

http://msdn.microsoft.com/en-us/library/0wh0045z.aspx

If you want control over interpolation modes see this post.

User · Answer

Just to add to yamen s answer  which is perfect for images but not so much for text   If you are trying to use this to scale text  like say a Word document  which is in this case in bytes from Word Interop   you will need to make a few modifications or you will get giant bars on the side   May not be perfect but works for me    using  MemoryStream ms   new MemoryStream wordBytes         float width   3840      float height   2160      var brush   new SolidBrush Color White        var rawImage   Image FromStream ms       float scale   Math Min width   rawImage Width  height   rawImage Height       var scaleWidth     int  rawImage Width    scale       var scaleHeight    int  rawImage Height   scale       var scaledBitmap   new Bitmap scaleWidth  scaleHeight        Graphics graph   Graphics FromImage scaledBitmap       graph InterpolationMode   InterpolationMode High      graph CompositingQuality   CompositingQuality HighQuality      graph SmoothingMode   SmoothingMode AntiAlias      graph FillRectangle brush  new RectangleF 0  0  width  height        graph DrawImage rawImage  new Rectangle 0  0   scaleWidth  scaleHeight         scaledBitmap Save fileName  ImageFormat Png       return scaledBitmap

User · Answer

Target parameters   float width   1024  float height   768  var brush   new SolidBrush Color Black     Your original file   var image   new Bitmap file     Target sizing  scale factor    float scale   Math Min width   image Width  height   image Height     The resize including brushing canvas first   var bmp   new Bitmap  int width   int height   var graph   Graphics FromImage bmp       uncomment for higher quality output   graph InterpolationMode   InterpolationMode High    graph CompositingQuality   CompositingQuality HighQuality    graph SmoothingMode   SmoothingMode AntiAlias   var scaleWidth    int  image Width   scale   var scaleHeight    int  image Height   scale    graph FillRectangle brush  new RectangleF 0  0  width  height    graph DrawImage image    int width - scaleWidth  2    int height - scaleHeight  2  scaleWidth  scaleHeight     And don t forget to do a bmp Save filename  to save the resulting file

[c#] Scaling a System.Drawing.Bitmap to a given size while maintaining aspect ratio

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