Resize images and save output

Question

I see many questions/Answers about resizing images here on SO.

But I can't find the correct one that fit my case.

In this post, it works only when you want to have a small image from a big one.

However if you have a picture with 24x24 dimension and you want to resize it to 256x256 dimension, the procedure will fail and gives you a distorted picture.

The code below is my attempt to sort out my issue

  Graph := TBitmap.Create;
  try   // After loading a .bmp file to Image1 with 48x48 dimension 
    Graph.Assign( Image1.Picture.Bitmap );
    Graph.Canvas.StretchDraw(Rect(0, 0, 255, 255), Graph);
    Graph.SetSize(255,255);
    Graph.SaveToFile('Location\Resault.bmp');
  finally
    Graph.Free;
  end;

The original image:

The result (the white square with the black part on the upper left):

How can we load an image to a TImage and convert/resize it and save changes?

Use a temp Bitmap with 255x255 and StretchDraw the small one on it. then assign back to `Graph` if you wish. do not expect to see great results when resizing a small image into a big one. — kobik, Aug 28 '17 at 12:53
or that @Sami http://chrislema.com/how-to-resize-images-to-make-them-larger-without-losing-quality/ — Andy K, Aug 28 '17 at 12:57

Ilyes · Accepted Answer · 2017-08-28T13:38:16.333

3

Thanks to kobik for the comment, it was useful.

var Graph : TBitmap; Conv : TBitmap;
begin

      Graph := TBitmap.Create;
      try
        Graph.Assign( Image1.Picture.Bitmap );
        Conv := TBitmap.Create;
        try
          Conv.SetSize(255,255);
          Conv.Canvas.StretchDraw(Rect(0, 0, 255, 255), Graph);
          Conv.SaveToFile('Location\Resault.bmp');   
        finally
          Conv.Free;
        end;

      finally
        Graph.Free;
      end;

end;

edited Aug 28 '17 at 13:38

answered Aug 28 '17 at 13:10

Ilyes

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1

In this code, you can remove the Graph variable and directly use Image1.Picture.Bitmap – Patrick PREMARTIN Aug 28 '17 at 18:25
2

You mean 256 when you say 255 – David Heffernan Aug 28 '17 at 20:34
@PatrickPREMARTIN Well, I have done that and It always extended the image with black background. Then, it saved it as it was shown on the TImage. This was the only way I was able to successfully resize and save... – ThN Feb 17 '19 at 09:17
@ThN Do you use VCL or FMX ? – Patrick PREMARTIN Feb 18 '19 at 20:04
StretchDraw will look terrible, I'd use GR32 resamplers. – hikari Aug 17 '20 at 06:53
Or maybe not, bicubic looks really blurry for this image https://i.imgur.com/1f9ctr8.png – hikari Aug 17 '20 at 07:46

Resize images and save output

1 Answers1