Crash in app

[biologic]

Maybe someone more experienced in LAMW can help.

Many thanks.

[biologic]

The code I want to make is :

- Open a bitmap with a press on a button (done)
- Show rhe bitmap on the form (done)
- with a press on 'convert' button, change the pixels to grayscale of the opened bitmap,
and show the changed bitmap on the form.
- with a press on the 'save' button, save this new gray bitmap.

I'm stuck in step 3, convert bitmap to grayscale.

[biologic]

I Found a good resource on Bitmaps in one of the AppDrawingInBitmap examples.

https://en.proft.me/2017/08/2/how-work-bitmap-android/

[biologic]

Anyone knows how to read/write a pixel from a jBitmap/jCanvas ?

[dseligo]

I don't have time to test it now, but ...

Try to use BitmapToArrayOfJByte method, something like:

Code: Pascal  [Select][+][-]

1. var
2.   posX, posY, bitmapWidth, bitmapHeight, bytesByLine: Word;
3.   red, green, blue: Integer;
4.   ABmp: jBitmap;
5.   baBmp: TDynArrayOfJByte;
6.   iNumPixels: Integer;
7. begin
8.   ... // load image to ABmp
9.   ...
10.   bitmapWidth := ABmp.GetWidth();
11.   bitmapHeight := ABmp.GetHeight();
12.   bytesByLine := Ceil(bitmapWidth / 8);
13.   baBmp := nil;
14.   iNumPixels := ABmp.BitmapToArrayOfJByte(baBmp); // to array in RGBA format
15.  
16.   for posY := 0 to bitmapHeight - 1 do // for every row
17.   begin
18.     While j < bitmapWidth do // for every column
19.     begin
20.       For k := 0 to 7 do // for every bit bit in column byte
21.       begin
22.         posX := j + k;
23.         if posX < bitmapWidth then // it doesn't have to be whole byte at last column
24.         begin
25.           // RGB values, I don't need alpha channel (alpha channel is +3)
26.           red   := Byte(baBmp[ posY * bitmapWidth * 4 + posX * 4 + 0 ]);
27.           green := Byte(baBmp[ posY * bitmapWidth * 4 + posX * 4 + 1 ]);
28.           blue  := Byte(baBmp[ posY * bitmapWidth * 4 + posX * 4 + 2 ]);
29.           ...
30.           // you can do something now with pixel RGB values
31.         end;
32.       end;
33.       j := j + 8;
34.     end;
35.   end;
36.   ...
37.   // convert it to new bitmap
38. end;

I didn't convert back to bitmap, because I am printing to POS printer. I see that methods GetBitmapFromJByteArray and SetByteArrayToBitmap exists, probably you can use them to get bitmap back from byte array.

[biologic]

Thank you. 

I will try this as soon as I can.
Next weekend probably.

[biologic]

If I want to call the getPixels method of the Bitmap Java object,
can this be done inside the project code ?

Or

Something different to do ?

Thanks

[biologic]

I found a good explanation at Chatgpt.