Scale an image nicely in Delphi?

Question

I'm using Delphi 2009 and I'd like to scale an image to fit the available space. the image is always displayed smaller than the original. the problem is TImage Stretch property doesn't do a nice job and harms the picture's readability.

I'd like to see it scaled like this instead:

Any suggestions how best to do this? Tried JVCL, but it doesn't seem to have this ability. A free library would be nice but maybe there's a low cost library that does "only" this would be good as well.

Answer 1

You really, really want to use Graphics32.

procedure DrawSrcToDst(Src, Dst: TBitmap32);
var
  R: TKernelResampler;  
begin
  R := TKernelResampler.Create(Src);
  R.Kernel := TLanczosKernel.Create;
  Dst.Draw(Dst.BoundsRect, Src.BoundsRect, Src);
end;

You have several methods and filters to choose when resampling an image. The example above uses a kernel resampler (kinda low, but with great results) and a Lanczos filter as reconstruction kernel. The above example should work for you.

Answer 2

The MadExcept library also has an image resize routine - see this topic. It is "free for non-commercial usage".

Answer 3

If you revert to using Win32 API calls, you can use SetStretchBltMode to HALFTONE and use StretchBlt. I'm not sure if this is provided using default Delphi calls, but that's the way I generally solve this issue.

Answer 4

You could try the built-in Delphi ScaleImage from GraphUtil

Answer 5

I use GDIPOB.pas's TGPGraphics class

if Canvas is TGPGraphics, Bounds is TGPRectF and NewImage is TGPImage instance:

Canvas.SetInterpolationMode(InterpolationModeHighQualityBicubic);
Canvas.SetSmoothingMode(SmoothingModeHighQuality);
Canvas.DrawImage(NewImage, Bounds, 0, 0, NewImage.GetWidth, NewImage.GetHeight, UnitPixel);

You can choose the quality VS speed factor by changing the interpolation mode

InterpolationModeDefault             = QualityModeDefault;
InterpolationModeLowQuality          = QualityModeLow;
InterpolationModeHighQuality         = QualityModeHigh;
InterpolationModeBilinear            = 3;
InterpolationModeBicubic             = 4;
InterpolationModeNearestNeighbor     = 5;
InterpolationModeHighQualityBilinear = 6;
InterpolationModeHighQualityBicubic  = 7;

and smooting mode:

SmoothingModeDefault     = QualityModeDefault;
SmoothingModeHighSpeed   = QualityModeLow;
SmoothingModeHighQuality = QualityModeHigh;
SmoothingModeNone        = 3;
SmoothingModeAntiAlias   = 4;

NOTE: This would require XP or later or bundeling the gdiplus.dll in your installer.