How to get R,G,B values of pixels in TLazIntfImage?
lazarus / 39-Graphics

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domasz · 2024-05-07 08:32

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 for y:=0 to
Bitmap.Height-1 do    for x:=0 to Bitmap.Width-1 do begin      Col :=
Bitmap.Pixels[x,y];   
Is this the right approach? Will Col contain always R,G,B,A values
even if I load a monochrome image into TLazIntfImage?

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wp · 2024-05-07 09:26

You question is a bit unclear: The variable "Bitmap" and the usage of
the Pixels property suggest that it is a TBitmap, but then the post
title speaks of a TLazIntfImage...

If "Bitmap" is a TLazIntfImage the Pixels property refers to the
palette index in case of paletted images. Based on this, you would use
this palette index in the image palette and from that you'd get the
FPColor of the pixels at position X, Y:

Normally, however, images are not paletted nowadays, and you would use
the Colors property to get the color components Red, Green, Blue and
Alpha from any pixel, even for monochrome 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 var  img:
TLazIntfImage;  // or any TFPCustomImage descendant  col:
TFPColor;...  if img.UsePalette then    col :=
img.Palette[img.Palette[X, Y]]  else    col := img.Colors[x, Y];

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TRon · 2024-05-07 09:54

Correct me in case wrong but to my knowledge it is even so that
whenever there isn't a palette present the pixels property returns a
(simple) zero.

So indeed a bit of a confusing question perhaps caused by having mixed
some things together ?

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wp · 2024-05-07 10:09

Quote from: TRon on May 07, 2024, 11:54:37 amCorrect me in case wrong
but to my knowledge it is even so that whenever there isn't a palette
present the pixels property returns a (simple) zero.
Yes, just checked it. And the second step, retrieving the color of
that index zero from the non-existing palette, will result in an
access violation.

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domasz · 2024-05-07 10:28

There is something wrong with Colors. I read a JPEG and get a total
black image. The showmessage is never fired.

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 Laz:
TLazIntfImage;    Reader: TFPReaderJPEG;    x,y: Integer;    Col:
TFPColor;begin  Reader := TFPReaderJPEG.Create;  Laz :=
TLazIntfImage.Create(1,1);   Laz.LoadFromFile('test.jpg', Reader);  
for y:=0 to Laz.Height-1 do    for x:=0 to Laz.Width-1 do begin     
Col := Laz.Colors[x, y];      if Col.red <> 0 then showmessage('x'); 
 end;   Reader.Free;  Laz.Free;

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TRon · 2024-05-07 11:01

@domasz
The reason you get an empty image is because there is no space
reserved for the actual data (e.g. it is/was never part of the image).

What is your actual aim here ? To actually work with lazintfimage or
retrieve information about the colors ? Different answer, different
solution. see also wiki. Note that the number of options to initialize
tlazintimage properly is limited.

edit: a possible 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 procedure
TForm1.Button1Click(Sender: TObject);var  Img : TFPMemoryImage; 
Reader: TFPReaderJPEG;  Laz: TLazIntfImage;  x,y: Integer;  Col:
TFPColor;begin  // create reader.  // Note that initializing a reader
can be omitted as long as a filename  // is used that is recognized by
the (standard) reader and the depending  // reader (jpeg in this case)
is included in the uses clause.  Reader := TFPReaderJPEG.Create;  //
Create image  Img := TFPMemoryImage.Create(0,0);  // Load image using
jpeg specific reader  Img.LoadFromFile('test.jpg', Reader);  //
release reader on first opportunity it isn't needed anymore 
Reader.Free;   // create interface  Laz := TLazIntfImage.Create(0,0); 
// set description of the data 
Laz.DataDescription:=GetDescriptionFromDevice(0);  // match size of
the interface with that of the original image.  Laz.SetSize(Img.Width,
Img.Height);  // actually copy the content of the image. Conversion of
pixelformat happens  // automatically in case necessary. 
Laz.CopyPixels(Img);  // release image on first opportunity 
Img.Free;   // original code ...  // ... but for reading the rgba
values only that can be replaced with using  // Img variable in which
case there is no need to use lazintfImage at all  for y:=0 to
Laz.Height-1 do    for x:=0 to Laz.Width-1 do    begin      Col :=
Laz.Colors[x, y];      if Col.red <> 0 then showmessage('x');    end; 
Laz.Free;end;

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wp · 2024-05-07 11:53

TLazIntfImage stores the image in a TRawImage. This mainly consists of
a Description (TRawImageDescription) and a pointer to the pixel data.
The description defines how the color channels are arranged in the
data block. In your case there is no description, i.e. everything is
at zero and the LazIntfImage cannot distinguish between the color
channels.

The correct way to do it is described in https://wiki.freepascal.org/D
eveloping_with_Graphics#TLazIntfImage.LoadFromFile (EDIT: or you could
TRon's 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
TForm1.FormCreate(Sender: TObject);var  AImage: TLazIntfImage; 
lRawImage: TRawImage;begin  // create a TLazIntfImage with 32 bits per
pixel, alpha 8bit, red 8 bit, green 8bit, blue 8bit,  // Bits In
Order: bit 0 is pixel 0, Top To Bottom: line 0 is top 
lRawImage.Init; 
lRawImage.Description.Init_BPP32_A8R8G8B8_BIO_TTB(0,0); 
lRawImage.CreateData(false);  // false = Zeroing memory is not needed
since the image is read from the file later anyway.  AImage :=
TLazIntfImage.Create(0,0);  try    AImage.SetRawImage(lRawImage);   
// Load an image from disk.    // It uses the file extension to select
the right registered image reader.    // The AImage will be resized to
the width, height of the loaded image.    AImage.LoadFromFile('lazarus
/examples/openglcontrol/data/texture1.png');  finally    AImage.Free; 
end; 
Quite complicated...

An easier way to setup a LazIntfImage correctly is to create an LCL
TGraphics instance which knows the correct raw image description and
to create the LazIntfImage from that:
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  jpeg:
TJpegImage;begin  jpeg := TJpegImage.Create;  laz :=
jpeg.CreateIntfImage;  laz.LoadFromFile(...);  // reader normally not
needed since it is determined automatically from the file extension.
Depending on why you need the IntfImage there is maybe an even simpler
method: You could use a TFPMemoryImage rather than a TLazIntfImage, it
takes the pixel layout from the image itself. The disadvantage is that
it takes more effort to display it in the LCL than with an IntfImage.
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 
FPImage, FPReadJPEG;var  img: TFPMemoryImage;begin  img :=
TFPMemoryImage.Create(0,0);  try    img.LoadFromFile('test.jpg');   
for y := 0 to img.Height-1 do      for x := 0 to img.Width -1 do     
 if img.Colors[x, y].Red <> 0 then ShowMessage('red detected'); 
finally    img.Free;  end;end;

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domasz · 2024-05-07 13:45

Thank you both!