AreaAveragingScalingFilter

[Aleksei Ivanov]

Hi Jeremy,

The intention could be /to pass through/ if the value of hints is 
different from the needed ones. That is the filter activates if and only 
if |hints == neededHints|, otherwise it doesn't do anything and forwards 
calls to its superclass.

-- 
Regards,
Alexey

On 17/04/2023 09:53, Jeremy Wood wrote:
> 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 iseffectively 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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