Thumbnails

[TRNelson]

I want to create a small function will generate a thumbnail from an image file.  It seems very straightforward.  The following code seems to work well for JPEG files.

Code: Pascal  [Select][+][-]

1. var
2.   MyPicture                            : TJpegImage;
3.   Thumbnail                            : TJpegImage;
4. begin
5.   MyPicture := TJpegImage.Create;
6.   Thumbnail := TJpegImage.Create;
7.   try
8.     MyPicture.LoadFromFile(some jpeg file);
9.     ThumbNail.Width  := 100;
10.     ThumbNail.Height := 100;
11.     ThumbNail.Canvas.StretchDraw(Rect(0, 0, 100, 100), MyPicture);
12.     Thumbnail.SaveToFile(thumbnail jpeg file);
13.   finally
14.     MyPicture.Free;
15.     Thumbnail.Free;
16.   end;
17. end;

And that would pretty much be it.  However, I want to make it a little more general so that it can do its stuff with different graphic formats (eg: PNG, TIFF, BMP and other supported formats).  It was suggested in some online documentation that you could use TPicture.  The thumbnail would be a JPEG file.  A slight modification to the code would be required.

Code: Pascal  [Select][+][-]

1. var
2.   MyPicture                            : TPicture;
3.   Thumbnail                            : TJpegImage;
4. begin
5.   MyPicture := TPicture.Create;
6.   Thumbnail := TJpegImage.Create;
7.   try
8.     MyPicture.LoadFromFile(some jpeg file);
9.     ThumbNail.Width  := 100;
10.     ThumbNail.Height := 100;
11.     ThumbNail.Canvas.StretchDraw(Rect(0, 0, 100, 100), MyPicture);
12.     Thumbnail.SaveToFile(thumbnail jpeg file);
13.   finally
14.     MyPicture.Free;
15.     Thumbnail.Free;
16.   end;
17. end;

The compiler complains about incompatible types for StretchDraw. 

Probably missing something very fundamental here but I can't see it.

[Mando]

Hi:

Try this:

Code: Pascal  [Select][+][-]

1.  ThumbNail.Canvas.StretchDraw(Rect(0, 0, 100, 100), MyPicture.graphic);
2.  

However, your code obtains square images (100x100), regardless of  the aspect of the original image.


I had this code:

Code: Pascal  [Select][+][-]

1. var
2.   escX, escY: Extended;
3.   img:TJPEGImage;
4.   min:TJPEGImage;
5.     r: TRect;
6. begin
7.    img:=TJPEGImage.Create; min:=TJPEGImage.Create;
8.  
9.   img.LoadFromFile((fichero));                  
10.  
11.   escX:=400/img.width; escY:=300/img.height; if escX>escY then escX:=escY;
12.  
13.   min.SetSize(round(img.width*escX),round(img.Height*escX));
14.   r:=Rect(0,0,min.Width,min.height);
15.   min.Canvas.AntialiasingMode:=amON;
16.   min.Canvas.StretchDraw(r,img);
17. ...
18.  

regards.

[TRNelson]

Well there you go!   

Thanks for that.  Not sure how I missed that.

As far as the squareness of the thumbnails, I was just setting up an example.  The final program will maintain the aspect ratios.

Thanks again!