AreaAveragingScalingFilter

[Jeremy Wood]

I could be mistaken, but it looks like AreaAveragingFilter has a typo in 
it. This method looks suspicious to me:

public void setHints(int hints) {
passthrough = ((hints & neededHints) != neededHints);
super.setHints(hints);
}

Later on the passthrough field is used as:

public void setPixels(int x, int y, int w, int h,
ColorModel model, byte pixels[], int off,
int scansize) {
if (passthrough) {
super.setPixels(x, y, w, h, model, pixels, off, scansize);
     } else {
         accumPixels(x, y, w, h, model, pixels, off, scansize);
     }
}

This makes me think we want passthrough to be true when we match 
specific hints (“neededHints”) promising to deliver the pixel data in 
whole scanlines from top-to-bottom. So the “!=“ in setHints(..) should 
be “==“.

If I set passthrough to true for BufferedImages (which always deliver 
pixels from top to bottom in entire scanlines), then the execution time 
of this filter reduces to less than 5% of its current time. But it 
introduces scaling artifacts and looks lower quality.

So if (?) my theory is correct that there is a typo, and knowing that 
the AreaAveragingFilter is effectively internally deprecated 
<https://bugs.openjdk.org/browse/JDK-6196792?jql=status = Open AND text 
~ "AreaAveragingScaleFilter"> : is anyone interested in discussing this 
with me further? I attached my (very rough) test program that 
demonstrates both the performance difference and the scaling artifacts.

(My broad goal is to create thumbnails of large images. If I used a 
Graphics2D to scale the image more than 50%, then I also see scaling 
artifacts with that approach. I know “Filthy Rich Clients” outlined a 
solution to that problem, but it’s expensive. So I’m dusting off this 
filter to see if it can work.)

Regards,
  - Jeremy
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