Working (resizing, padding, splitting) with 16 bit png and 8bit png
images?
lazarus / 39-Graphics

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FiftyTifty · 2023-01-08 11:54

I've been pulling my hair out with trying to get a tool made to work
with 16 bit greyscale png, as well as 24 bit colour png. I've given up
on doing it with Python, as the libraries that work with 16bit png
files are all sorts of wonky and have incorrect documentation.

After doing some research, it seems that only Vampyre Imaging Library
works with 16 bit greyscale png files, so I'm using that for now. If
there's a better one, let me know.

What I have to do, is take a 4096x4096 image (image divisible by 256),
and pad out the bottom & right sides of the image with black until it
is 4112x4112 (divisible by 257). Then, split the image into 257x257
images by x&y coordinates.

How do I pad the image from being 4096x4096, into 4112x4112? My main
idea was to create two images, fill them with black, and append them
to the original.

Don't see a way to do that though.

Here is my current 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 procedure
TformWindow.buttonHeightmapClick(Sender: TObject);var   imageCurrent,
imageResized, imageFillX, imageFillY: TSingleImage;   iSizeX, iSizeY,
iAddX, iAddY: Integer;   strImageToSave: string;   infoCurrent:
TImageFormatInfo;begin   if dialogOpen.Execute then begin    
imageCurrent := TSingleImage.CreateFromFile(dialogOpen.FileName);   
strImageToSave := ExtractFileNameWithoutExt(dialogOpen.FileName);    
imageResized := TSingleImage.CreateFromImage(imageCurrent);    iSizeX
:= imageCurrent.Height;    iSizeY := imageCurrent.Width;    
GetImageFormatInfo(imageCurrent.Format, infoCurrent);     //We want:
'png' = DetermineFileFormat(dialogOpen.FileName)    //16 bit png:
infoCurrent.BytesPerPixel = 2;    //Greyscale 1 ChannelAlpha:
infoCurrent.ChannelCount = 1;    
ShowMessage(DetermineFileFormat(dialogOpen.FileName) + ' '      +
inttostr(infoCurrent.BytesPerPixel * 8) + 'bit '      +
inttostr(infoCurrent.ChannelCount) + ' channel'    );     iAddX := 257
- (iSizeX mod 257);    iAddY := 257 - (iSizeY mod 257);     imageFillX
:= TSingleImage.CreateFromParams(257, iAddY, imageCurrent.Format);   
imageFillY := TSingleImage.CreateFromParams(iAddX, 1,
imageCurrent.Format);     //Somehow pad out imageCurrent until it is
4112x4112   end;  end;

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circular · 2023-01-08 14:21

Hello FiftyTifty,

You could do that thing you want to do by creating an image for each
target square of the grid and put the content of the source image in
it with the appropriate offset.

I don't know how to do it with Vampyre Imaging Library, though I can
tell you how to do it with BGRABitmap. It provides a TExpandedBitmap
class that has 16bit per channel. It is not grayscale but RGBA, so it
will used 4x more memory. But it can read and write 16-bit ("word-
sized") grayscale PNG images.

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
ExpandedBitmap, BGRABitmapTypes, BGRAWritePNG; procedure
GetSquares(ASourceFile: string; ADestFilePrefix: string; ATileSize:
integer = 257);var  source, dest: TExpandedBitmap;  ofsX, ofsY, nbX,
nbY, ix, iy: integer;  writer: TBGRAWriterPNG;begin  source :=
TExpandedBitmap.Create;  source.LoadFromFile(ASourceFile);  nbX :=
(source.Width+ATileSize-1) div ATileSize;  nbY :=
(source.Width+ATileSize-1) div ATileSize;  ofsX := (nbX*ATileSize -
source.Width) div 2;  ofsY := (nbY*ATileSize - source.Height) div 2; 
writer := TBGRAWriterPNG.Create;  writer.GrayScale := true; 
writer.WordSized := true;  writer.UseAlpha := false;  for iy := 0 to
nbY-1 do  for ix := 0 to nbX-1 do  begin    dest :=
TExpandedBitmap.Create(ATileSize, ATileSize, BGRABlack);   
dest.PutImage(ofsX - ix*ATileSize, ofsY - iy*ATileSize, source,
dmSet);    dest.SaveToFile(ChangeFileExt(ADestFilePrefix, '') +     
IntToStr(ix) + '-' + IntToStr(iy) + '.png', writer);    dest.Free; 
end;  writer.Free;  source.Free;end;
Regards

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marcov · 2023-01-08 14:31

Afaik fcl-image that comes with FPC can do 16-bit grayscale ?

If you get stuck somewhere with fcl-image, please talk about it here,
or file a bug.

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FiftyTifty · 2023-01-08 19:38

Quote from: marcov on January 08, 2023, 03:31:29 pmAfaik fcl-image
that comes with FPC can do 16-bit grayscale ?

If you get stuck somewhere with fcl-image, please talk about it here,
or file a bug.

Thanks for the info you two. I'll try with FCLImage first, as it
appears to have the widest file format support. And actual examples on
using it.

The first issue I've found is pen.FPColor for setting the colour of
the black rectangle. There is no example in the wiki of setting a
colour. How do we do that? In this case, I want it to be pure black
(0).

Here's the code so far:

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   if
dialogOpen.Execute then begin     imageCurrent :=
TFPMemoryImage.LoadFromFile(dialogOpen.FileName);    canvasCurrent :=
TFPImageCanvas.create(imageCurrent);    writerCurrent :=
TFPWriterPNG.Create;     //Get size of the heightmap    iSizeX :=
imageCurrent.Height;    iSizeY := imageCurrent.Width;     //Get number
of pixels needed to make image divisible by 257    iAddX := 257 -
(iSizeX mod 257);    iAddY := 257 - (iSizeY mod 257);     //Set canvas
to the size we want    canvasCurrent.Width := iSizeX + iAddX;   
canvasCurrent.Height := iSizeY + iAddY;     //Fill added rows with
black    with canvas do begin       pen.mode := pmBlack;     
pen.style := psSolid;      pen.width := 1;      pen.FPColor := ;    
end;     canvasCurrent.FillRect(iSizeX + 1, iSizeY + 1,              
           canvasCurrent.Width, canvasCurrent.Height                 
        );   end;
Right, did some more work. Now I got it to output an image, but it's a
total mess. Mostly black with a couple strips of the source image
coming through. I'll attach the project and the heightmap I'm using.

Here's the resulting heightmap: (https://i.imgur.com/ydZO386.png)

Project: https://mega.nz/file/XwNCmayZ#0MuwF4X-
t75jXlccRxVL5N3ZCqKn984R3yr0HON1uf0

Code:

Code: [Select]procedure TformWindow.buttonHeightmapClick(Sender:
TObject);
var
   imageCurrent: TFPCustomImage;
   canvasCurrent: TFPCustomCanvas;
   readerCurrent: TFPCustomImageReader;
   writerCurrent: TFPCustomImageWriter;
   iSizeX, iSizeY, iAddX, iAddY: Integer;
   strImageCurrent, strImageToSave: string;
begin

  if dialogOpen.Execute then begin

    strImageCurrent := dialogOpen.FileName;
    imageCurrent := TFPMemoryImage.Create(0, 0);
    imageCurrent.LoadFromFile(strImageCurrent);
    canvasCurrent := TFPImageCanvas.create(imageCurrent);
    writerCurrent := TFPWriterPNG.Create;

    //Get size of the heightmap
    iSizeX := imageCurrent.Height;
    iSizeY := imageCurrent.Width;

    //Get number of pixels needed to make image divisible by 257
    iAddX := 257 - (iSizeX mod 257);
    iAddY := 257 - (iSizeY mod 257);

    //Set canvas to the size we want
    canvasCurrent.Width := iSizeX + iAddX;
    canvasCurrent.Height := iSizeY + iAddY;

    //Fill added rows with black
    with canvas do begin

      pen.mode := pmBlack;
      pen.style := psSolid;
      pen.width := 1;
      pen.FPColor := TColorToFPColor(RGBToColor(0,0,0));

    end;

    ShowMessage('Canvas set');

    canvasCurrent.FillRect(iSizeX + 1, iSizeY + 1,
                           canvasCurrent.Width, canvasCurrent.Height
                           );

    imageCurrent.SaveToFile('Test.png', writerCurrent);

  end;

  writerCurrent.Free;
  readerCurrent.Free;
  canvasCurrent.Free;
  imageCurrent.Free;

  ShowMessage('Free finished!');


end;   
Edit2: Right, it turns out that resizing the canvas via:

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    
canvasCurrent.Width := iSizeX + iAddX;    canvasCurrent.Height :=
iSizeY + iAddY;
Is what corrupts the image. Not the rectangle being drawn.

Edit3: Same happens with:

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    
imageCurrent.SetSize(iSizeX + iAddX, iSizeY + iAddY);

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marcov · 2023-01-09 09:01

I don't use canvas for image operations. 

Whatever library I use, I get dimensions, bpp, rowpitch (*) and some
format enumerator. Then I get line pointers, and simply use
fillword/char etc.

(*) rowpitch is the jump between lines. which usually is (pixelsx*bpp)
rounded up to 32-bit, but can be negative for bottom-up images.

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wp · 2023-01-09 11:27

Quote from: FiftyTifty on January 08, 2023, 08:38:26 pmHere's the
resulting heightmap: (https://i.imgur.com/ydZO386.png)

Project: https://mega.nz/file/XwNCmayZ#0MuwF4X-
t75jXlccRxVL5N3ZCqKn984R3yr0HON1uf0
Please don't store attachments on external servers where they will be
gone sooner or later. Then this thread will become useless to anybody.
And I don't want to register at the mega.nz site just to have a look
at your project.

Pack the project files (*.pas, *.lfm, *.lpi, *.lpr plus required data
files) into a single zip which you can upload under "Attachments and
other options". There is a maximum upload limit which may become
problematic with large projects, but you should be aware that the
chance for somebody to look at your project decreases drastically with
the size of your project.

The image may be an exception to this rule since it is very large and
will probably exceed the upload limit.

I downloaded the image from the imgur server, but noticed that it is a
24bit image - I thought you are talking of 16-bit grayscale.

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FiftyTifty · 2023-01-09 17:01

Quote from: marcov on January 09, 2023, 10:01:23 amI don't use canvas
for image operations. 

Whatever library I use, I get dimensions, bpp, rowpitch (*) and some
format enumerator. Then I get line pointers, and simply use
fillword/char etc.

(*) rowpitch is the jump between lines. which usually is (pixelsx*bpp)
rounded up to 32-bit, but can be negative for bottom-up images.

That sounds pretty complex. Are there any tutorials on doing that with
Lazarus?

Quote from: wp on January 09, 2023, 12:27:15 pm-snip-

Yeah the image is converted to 8 bit RGB by imgur, and any image host
for that matter. The source image is 16 bit greyscale, which you'd see
if you downloaded the archive which contains the image. And it's too
large to zip and upload, as the image is 11MB, and the project around
30MB.