Bicubic or Bilinear interpolation adds magenta tone to scaled down image

[jai-interest-2]

I am scaling down a 3300x2550 image to 560x433. I need a good quality scaled down image.

If I use Bicubic or Bilinear interpolation then image has a magenta tone. When I use 'Nearest' interpolation I do not see this effect.

Is it something I am doing wrong?

Thanks,
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[jai-interest-2]

That's bizarre. The color should not change. Is your original image indexed-color (palette) or some such? Which versions of things are you using?

Brian

> I am scaling down a 3300x2550 image to 560x433. I
> need a good quality scaled down image.
>
> If I use Bicubic or Bilinear interpolation then image
> has a magenta tone. When I use 'Nearest'
> interpolation I do not see this effect.
>
> Is it something I am doing wrong?
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[jai-interest-2]

I should also have noted that the the SubsampleAverage operation would be worth checking out.

> That's bizarre. The color should not change. Is your
> original image indexed-color (palette) or some such?
> Which versions of things are you using?
>
> Brian
>
> > I am scaling down a 3300x2550 image to 560x433. I
> > need a good quality scaled down image.
> >
> > If I use Bicubic or Bilinear interpolation then
> image
> > has a magenta tone. When I use 'Nearest'
> > interpolation I do not see this effect.
> >
> > Is it something I am doing wrong?

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[jai-interest-2]

I know this is a long shot but I have the exact same issue, but i am using subsampleaverage, interpolation doesnt make a difference and for one gif in particular it always comes out magenta.

any help would be great.
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[jai-interest-2]

ok it was definitely something to do with the conversion of index color map which contained alpha(transperency), so i ended up just encoding it as a JPEG, and working on that.

if you prevent the conversion of the color map you end up with much degraded quality when scaling, so it was pretty much useless.
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[jai-interest-2]

I'm not sure if this is relevant but if you write an image with an alpha band to a JPEG it comes out looking like a martian landscape :)  This is because some when viewers see the fourth band in the JPEG they interpret it as a CMYK image and your ARGB data turns reddish.  Discard the alpha band and all should be well.

I ran into this problem recently and found the above info here:
http://pdf.jpedal.org/java-pdf-blog/bid/11403/Odd-coloured-JPEGs-in-Java-with-ImageIO#Comments

Michael
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