[filmscanners] Re: PS sharpening

["Julian Vrieslander" <julianv@mindspring.com>]

On 8/22/02 6:16 PM, "al@greenspace.freeserve.co.uk"
<al@greenspace.freeserve.co.uk> wrote:

> Maybe I misunderstood Anthony but I thought the (over) sharpening was meant to
> be applied BEFORE the downsampling to ensure that some elements of the
> exaggerated detail made it into the reduced image.

In my last message, I forgot to mention that I did try the multistep method
both ways:

sharpen->downsample...(repeat)...

and

downsample->sharpen...(repeat)...

I also tried varying the amount of sharpening at the reduction steps.

What I found was that I could get good results both ways.  Maybe very
slightly better when I did the sharpening before each 50% reduction, with a
smaller sharpening after the last reduction.  I also tried doing all steps
while the image was in LAB mode, sharpening only the L channel, and
converting back to RGB at the end.

But for each of the images that I made with the multistep method, I found
that I could get a very similar image by downsampling in one step, followed
by a single USM step.  I checked this by keeping the multistep-generated
image and the single-step image on screen at the same time, adjusting USM
params on the latter until they matched.

Maybe my eyes or my monitor are not good enough to discern the advantage of
the multistep voodoo.

--
Julian Vrieslander <julianv@mindspring.com>

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