Thumbnails
lazarus / 39-Graphics

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TRNelson · 2016-03-25 18:31

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][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i var 
MyPicture                            : TJpegImage;  Thumbnail        
                  : TJpegImage;begin  MyPicture := TJpegImage.Create; 
Thumbnail := TJpegImage.Create;  try    MyPicture.LoadFromFile(some
jpeg file);    ThumbNail.Width  := 100;    ThumbNail.Height := 100;  
ThumbNail.Canvas.StretchDraw(Rect(0, 0, 100, 100), MyPicture);   
Thumbnail.SaveToFile(thumbnail jpeg file);  finally   
MyPicture.Free;    Thumbnail.Free;  end;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][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i var 
MyPicture                            : TPicture;  Thumbnail          
                : TJpegImage;begin  MyPicture := TPicture.Create; 
Thumbnail := TJpegImage.Create;  try    MyPicture.LoadFromFile(some
jpeg file);    ThumbNail.Width  := 100;    ThumbNail.Height := 100;  
ThumbNail.Canvas.StretchDraw(Rect(0, 0, 100, 100), MyPicture);   
Thumbnail.SaveToFile(thumbnail jpeg file);  finally   
MyPicture.Free;    Thumbnail.Free;  end;end;
The compiler complains about incompatible types for StretchDraw. 

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

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Mando · 2016-03-25 19:14

Hi:

Try this:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
 ThumbNail.Canvas.StretchDraw(Rect(0, 0, 100, 100),
MyPicture.graphic); 

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


I had this code:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i var   escX,
escY: Extended;  img:TJPEGImage;  min:TJPEGImage;    r: TRect;begin 
 img:=TJPEGImage.Create; min:=TJPEGImage.Create;  
img.LoadFromFile((fichero));                      escX:=400/img.width;
escY:=300/img.height; if escX>escY then escX:=escY;  
min.SetSize(round(img.width*escX),round(img.Height*escX)); 
r:=Rect(0,0,min.Width,min.height); 
min.Canvas.AntialiasingMode:=amON;  min.Canvas.StretchDraw(r,img);... 


regards.

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TRNelson · 2016-03-25 19:51

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!