[BGRA] What's wrong with Resample Filters Lanczos2 and 4 ?
lazarus / 39-Graphics

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jipété · 2024-06-14 10:38

Hello,

I compare the rendering of the resampling filters and to do this, I
use an image that is modified by the 11 classic filters (Box, Linear,
etc.) and I noticed that when converting with The Gimp, always in the
same way, the .png generated by the graphics tool to bmp's for the
comparison tool, 2 files have an alpha channel (I don't know where it
comes from) and the 9 other files don't have one :
9+2_layers.png

Here is what I use to convert the base image:     
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      
img.Width  := Wd;       img.Height := Hd;      image.ResampleFilter :=
SelectedFilter; // image is a TBGRABitmap;// SelectedFilter is coming
from another procedure, procedure
TForm1.radiogroupResFiltersClick(Sender: TObject);// radiogroup Items
host the 11 filtersbegin  SelectedFilter :=
TResamplefilter(radiogroupResFilters.ItemIndex); 
imgPaint(nil);end;//      stretched := image.Resample(Wd, Hd) as
TBGRABitmap;That's all.

Of course, to watch the result, I then use
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       copy
:= image.MakeBitmapCopy(clNone);      img.Picture.Assign(copy); // and
img is a TImage      copy.Free;
This gives me a different rendering depending on the presence or
absence of the alpha channel, and depending on the display tool used,
one version or the other:
4resample.gif
Lanczos3--Lanczos4(or2).png

Is it a bug or a feature ?

Thanks,

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circular · 2024-06-14 17:54

Hi! I am not sure about the steps to reproduce the problem. Would you
have a sample program?

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jipété · 2024-06-14 22:21

Quote from: circular on June 14, 2024, 07:54:46 pmWould you have a
sample program?
Sorry but this afternoon I've changed the way sizes are set-up and
problem has disappeared.

I apologize for the inconvenience and you can delete that discussion,
if you want to free disk space.
Regards,

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circular · 2024-06-15 08:54

I am glad the problem is solved. This confirms the appearance of the
images that looks like a problem of pixel format.

Have a nice day