Image quality poor after loading into Image control in comparison to original

Question

I got an app that loads images into the Zimage(graphcontrol). One issue I am having is the original image is a lot better quality than the one that ends up showing in the component. The one showing looks like it has random black marks on it. So what I do:

• Load the image from a folder into TJpegimage

• Assign jpg to a bitmap

• Save bitmap to object list

• Repeat that above until all images are loaded into object list

• Then I create a bitmap

• Assign the first image in the object list to it

• Draw the bitmap on canvas

But it just looks a lot worse than the original. Any help or idea on this?

This is the loading code.

procedure TForm1.LoadImages(const Dir: string);
var
  i: Integer;
  CurFileName: string;
  JpgIn: TJPEGImage;
  BmpOut: TBitmap;
begin

//set up progress bar
 progressbar1.Min := 0;
 progressbar1.Max := GetFilesCount(dir,'*.*');
 Label3.Visible := true;
 progressbar1.Visible := true;
//sets array for length
  SetLength(hwArray,GetFilesCount(dir,'*.*'));
//sets index for object list
  CurIdx := -1;
  i := 0;
  while True do
  begin
//gets file name out of current folder
    CurFileName := Format('%s%d.jpg',
                          [IncludeTrailingPathDelimiter(Dir), i]);
    if not FileExists(CurFileName) then
      Break;
//count files in folder for progress bar.
     progressbar1.StepBy(1);
//creates jpgin
    JpgIn := TJPEGImage.Create;
    try
//loads jpgin with file
      JpgIn.LoadFromFile(CurFileName);
//creates TBitmap and sets width to same as jpgs
      BmpOut := TBitmap.Create;
      bmpout.Width := jpgin.Width;
      bmpout.Height := jpgin.Height;
     try
         BmpOut.Assign(JpgIn);
//adds 1 to index for object list. thus starting at 0
         curIdx := curIdx+1;
//add bitmap to objectlist
         CurIdx:= mylist.Add(TBitmap(bmpout));
         hwArray[CurIdx][0]:=jpgin.Width;
         hwArray[CurIdx][1]:=jpgin.height;

      finally
      end;
    finally
      JpgIn.Free;
    end;
    Inc(i);
  end;
//makes sure cout is above 0 thus files added
  if mylist.Count > 0 then
  begin
      try
      CurIdx := 0;
      getBitmapfromList(CurIdx,bmpout);
      ZImage1.Bitmap.Assign(bmpout);
       //image1.Canvas.Assign(bmpout);
    finally
       BmpOut.Free;
    end;
  end;
  Label3.Visible := false;
  progressbar1.Visible := false;
  page:= '0';
  zimage1.DblClick;
end;

function get bit map from list

procedure Tform1.getBitmapfromList(index:integer;var Bitm:TBitmap);
begin
     Bitm.Assign(TBitmap(mylist[index]));
     if (Bitm.Width<>hwArray[index][0]) OR (Bitm.Height<>hwArray[index][1]) then begin
        ShowMessage('Size differs');
        Bitm.Width:=hwArray[index][0];
        Bitm.Height:=hwArray[index][1];
     end;
end;

Button to view the next image:

procedure TForm1.Button3Click(Sender: TObject);
var
  BmpOut: TBitmap;
begin
  bmpout := TBitmap.Create;
  CurIdx:= strtoint(page);
  getBitmapfromList(CurIdx,bmpout);
  ZImage1.Bitmap.Assign(bmpout);
  //image1.Canvas.Assign(bmpout);
  page := inttostr(strtoint(page) +1);      //this should show next item in list?
  zimage1.Repaint;
end;

Thanks for any help or suggestions.

Here are the images:

---

EDIT:

It seems like once I zoom in on an image it gets better. the worst quality is when it's full screen/zoomed all the way out.. original size.

Answer 1

• a) I assume that all images have a different size. If the displayed image "ZImage1" should have always the same height or width (one of two things, or it is made ​​with stretch fit == low quality) must be determined ratio (orginal.height / original.width).Then "ZImage1" (either height or width) must calculated in the new relationship.
• b) Set ZImage1.AutoSize:=false;

• c) Set ZImage1.Stretch:=false;

• d) bmpout.Width and Height must set to the current mylist[CurIdx] size.

bmpout.Assign(TBitmap(mylist[CurIdx]));
Zimage1.Bitmap.Width := bmpout.Width;
Zimage1.Bitmap.Height := bmpout.Height;
ZImage1.Bitmap.Assign(bmpout);

NOTE:

You did NOT *assign* to mylist .. you store it CurIdx:= mylist.Add(TBitmap(bmpout));

I can not see how you have created "mylist".

Maybe that's the reason, if you want it back with bmpout.Assign(TBitmap(mylist[CurIdx]));, perhaps there is no automatic set bmpout.Width and bmpout.Height.

TIP:

create an extra array to store height and width.

....
JpgIn.LoadFromFile(CurFileName);
BmpOut := TBitmap.Create;
bmpout.Width := jpgin.Width;
bmpout.Height := jpgin.Height;
....
CurIdx:= mylist.Add(TBitmap(bmpout));
hwArray[CurIdx][0]:=jpgin.Width;
hwArray[CurIdx][1]:=jpgin.height;
....

make a procedure EDIT: put a test into it;

procedure getBitmapfromList(index:integer;var Bitm:TBitmap);
begin
     Bitm.Assign(TBitmap(mylist[index]));
     if (Bitm.Width<>hwArray[index][0]) OR (Bitm.Height<>hwArray[index][1]) then begin
        ShowMessage('Size differs');
        Bitm.Width:=hwArray[index][0];
        Bitm.Height:=hwArray[index][1];
     end;
end;

call it with:

....
getBitmapfromList(CurIdx,bmpout);
....
ZImage1.Bitmap.Assign(bmpout);
....  

EDIT: Create hwArray

type
  Tarray2size = Array[0..1] of integer;
.... 

var
  hwArray : Array of Tarray2size;
....

procedure TForm1.LoadImages(const Dir: string);
....
begin
 //set up progress bar
 progressbar1.Min := 0;
 showmessage(inttostr(GetFilesCount(dir,'*.*')));
 SetLength(hwArray,GetFilesCount(dir,'*.*'));
....