Unable to use Scale method in TJPEGImage
lazarus / 39-Graphics

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jrmit · 2010-01-27 16:24

TJPEGImage.Scale will not compile

I am fairly new to Lazarus and was trying to port an application from
Delphi for resizing Jpeg images to various screen resolutions (such as
1400x900), but ran into a problem with TJPEGImage.Scale.  It appears
Scale is not supported in Lazarus' implementation of TJPEGImage.  Any
suggestions.

procedure TForm1.btnResizeImageClick(Sender: TObject);
var
  Jpeg1, Jpeg2: TJPEGImage;
  TempBitmap : TBitMap;
  CanvasRect : TRect;
  x, nscale : integer;
  aspect, maxaspect : single;
  picdisp : String;
begin
  x := lbxFileListBox.ItemIndex;
  picdisp := lbxFileListBox.Items;
  TempBitmap := TBitmap.Create;
  Jpeg1 := TJPEGImage.Create;
  Jpeg2 := TJPEGImage.Create;
  try
    Jpeg1.LoadFromFile(picdisp);
    //Find the width and height which fits inside the maximum
rectangle
    //while preserving the aspect ratio
    aspect := Jpeg1.Width /Jpeg1.Height;
    maxaspect := sw / sh;
    if (aspect > maxaspect) then
    begin
      TempBitmap.Width := sw;
      TempBitmap.Height := round(sw / aspect);
    end
    else
    begin
      TempBitmap.Width := round(sh * aspect);
      TempBitmap.Height := sh;
    end;
    //Find the scale that causes the jpg to be as small as possible
while
    //still larger than the destination width and height.  This
ensures that
    //when the image is resampled it doesn't increase any dimention,
only downsize
    nscale :=floor(min(Jpeg1.Width / TempBitmap.Width, Jpeg1.Height
/TempBitmap.Height));
    case nscale of
      0..1: begin
        Jpeg1.Scale := jsFullSize;  Error: identifier indents no
member "Scale"
        nscale := 1;
      end;
      ... more code

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theo · 2010-01-27 17:34

There is Canvas.StretchDraw
http://lazarus-
ccr.sourceforge.net/docs/lcl/graphics/tcanvas.stretchdraw.html

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jrmit · 2010-01-28 15:35

Thanks, Theo.  Actually, I am already using canvas.stretchdraw further
down in the code (not shown).  I will revise the code not to use
TJPEGImage.Scale.

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jrmit · 2010-03-25 15:34

Since JPEGImage.Scale and Scanline were not available in Lazarus I
modified the resize (resample) procedure using some code derived from
(www.efg2.com/Lab ImageProcessing/AspectRatio.htm).

    Jpeg1.LoadFromFile(picdisp);
    .
    . 
    if   Jpeg1.Width / Jpeg1.Height  <  sw / sh then
    begin
      CanvasRect.Top    := 0;
      CanvasRect.Bottom := NBitmap.Height;
      wt := MathRound((NBitmap.Height * Jpeg1.Width) / Jpeg1.Height);
      Half := (NBitmap.Width - wt) div 2;
      CanvasRect.Left  := Half;
      CanvasRect.Right := CanvasRect.Left + wt;
    end
    else
    begin
      CanvasRect.Left    := 0;
      CanvasRect.Right   := NBitmap.Width;
      ht := MathRound((NBitmap.Width * Jpeg1.Height) / Jpeg1.Width);
      Half := (NBitmap.Height - ht) div 2;
      CanvasRect.Top    := Half;
      CanvasRect.Bottom := CanvasRect.Top + ht;
    end;
    .
    .
  end;

Read More: microguyscube.com/index.php/image-modify-procedure-for-
lazarus

John
www.microguyscube.com

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derek.john.evans · 2013-02-02 04:20

I also wanted the Scale property in Lazarus. I tried using
TFPMemoryImage and TFPReaderJpeg, but the images came out with pixels
missing. But, I found this solution:

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 uses
FPReadJPEG, IntfGraphics; // May require other units type  
TJPEGImagePlus = class(TJPEGImage)  private    FScale: TJPEGScale; 
protected    procedure InitializeReader(AImage: TLazIntfImage;     
AReader: TFPCustomImageReader); override;  public    property Scale:
TJPEGScale read FScale write FScale;  end; procedure
TJPEGImagePlus.InitializeReader(AImage: TLazIntfImage;  AReader:
TFPCustomImageReader);begin  (AReader as TFPReaderJpeg).Scale :=
FScale;  inherited;end; 
Then just load the JPEG's as you normally do via TJpegImage:
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  
LJPEGImage := TJPEGImagePlus.Create;  LJPEGImage.Scale := jsEighth; 
LJPEGImage.LoadFromFile(AFileName);  FPicture.Assign(LJPEGImage); 
FreeAndNil(LJPEGImage);  Hope that helps people.

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BigChimp · 2013-02-02 07:55

Guys,

Great that you have improvements for Lazarus.

If they're good enough, could you please post them as patches to
bugtracker issues? That way, they won't be forgotten or overlooked.
See e.g.
http://wiki.lazarus.freepascal.org/Creating_A_Patch
and
http://wiki.lazarus.freepascal.org/How_do_I_create_a_bug_report

Thanks a lot!