Mike Williams <nos### [at] econymdemoncouk> wrote:
> The freeware IrfanView can do it. In its "Image Resize/Resample" pane
> you need to select "Resample" rather than "Resize".

Thanks Mike,

   I've downloaded the software and I had a few questions.  Can someone tell
me what the difference is between these filters:

Lanczos
Hermite
Triange
Mitchell
Bell
B-Spline

The help didn't tell me much.  In fact it confused me more by stating "some
Resample filter can be used if you are enlarging the image."  Since I'm
wanting to shrink the image is this telling me that IrfranView just uses
the "resize" function when it reduces the image?  I'd like the pixels to be
averaged together and I assume these filters apply different weighted
averages but I'd like to be sure of what its doing.

Thanks,
Carl

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Wasn't it Carl who wrote:
>Mike Williams <nos### [at] econymdemoncouk> wrote:
>> The freeware IrfanView can do it. In its "Image Resize/Resample" pane
>> you need to select "Resample" rather than "Resize".
>
>Thanks Mike,
>
>   I've downloaded the software and I had a few questions.  Can someone tell
>me what the difference is between these filters:
>
>Lanczos
>Hermite
>Triange
>Mitchell
>Bell
>B-Spline
>
>The help didn't tell me much.  In fact it confused me more by stating "some
>Resample filter can be used if you are enlarging the image."  Since I'm
>wanting to shrink the image is this telling me that IrfranView just uses
>the "resize" function when it reduces the image?  I'd like the pixels to be
>averaged together and I assume these filters apply different weighted
>averages but I'd like to be sure of what its doing.

I've no idea about the difference between the filters, but "Resample"
and "Resize" are not the same thing when reducing.

I tried a test image that had lots of one-pixel-wide black lines. Using
"Resize" caused some pixels to be lost and some pixels to remain black.
All the "Resample" filters retained all parts of the lines and reduced
them to 50% grey. All the filters worked equally well when reducing, so
perhaps the differences between the filter settings is only meaningful
when enlarging.

When it comes to enlarging an image, the different filters give visibly
different compromises between sharpness and aliasing.

-- 
Mike Williams
Gentleman of Leisure

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