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scaling

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scaling Andrew 24 Sep 13:25
  scaling Bettina Lechner 24 Sep 21:51
23f4e3390709241601r44d8b102... 07 Oct 20:18
  scaling Andrew 25 Sep 08:25
   scaling David Gowers 25 Sep 09:31
    scaling Sven Neumann 27 Sep 09:12
Andrew
2007-09-24 13:25:28 UTC (over 17 years ago)

scaling

Hi,

How does 'sinc (lanczos3)' interpolation compare with the others for quality?

TIA

Andrew

Bettina Lechner
2007-09-24 21:51:44 UTC (over 17 years ago)

scaling

hi!

as far as I now it's the best one. but the algorithm is very complicated to explain. I don't even understand the first sentences in wikipedia.

http://en.wikipedia.org/wiki/Lanczos_algorithm

HTH tina

Am 24.09.2007 13:25 Uhr schrieb "Andrew" unter :

Hi,

How does 'sinc (lanczos3)' interpolation compare with the others for quality?

TIA

Andrew
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Andrew
2007-09-25 08:25:02 UTC (over 17 years ago)

scaling

David Gowers wrote:

On 9/24/07, Andrew wrote:

Hi,

How does 'sinc (lanczos3)' interpolation compare with the others for quality?

For upscaling, it's roughly like sharpening the image and scaling it up with Linear interpolation. That is not the method, just how the result looks.
Arguably this counters the typical blurring incurred by upscaling. Personally I've always preferred manual sharpening to using Lanczos.

Lanczos downscaling is interesting, but you won't find that in your copy of gimp -- it's still being worked on.

The Wikipedia article certainly was over my head.

From what I read on the Gimp bug page lanczos scaling is not yet perfect. (But then what is?)

I have to upscale images from 16M to 48M and it seems the client takes them apart and looks at them through a microscope and rejects them if there are signs of sharpening or interpolation artefacts.

So far as I can see, my Gimp (2.4.0-rc2) does have lanczos downscaling

Thanks for your help,

Andrew

David Gowers
2007-09-25 09:31:04 UTC (over 17 years ago)

scaling

On 9/25/07, Andrew wrote:

The Wikipedia article certainly was over my head.

From what I read on the Gimp bug page lanczos scaling is not yet perfect. (But then what is?)

I have to upscale images from 16M to 48M and it seems the client takes them apart and looks at them through a microscope and rejects them if there are signs of sharpening or interpolation artefacts.

So far as I can see, my Gimp (2.4.0-rc2) does have lanczos downscaling

I know. That is why I made a point of saying it doesn't. It has some strange facsimile of Lanczos downscaling. If you compare ImageMagick's implementation with GIMP's, you can see a clear difference (and that ImageMagick gives better looking results.)

For your requirements, if you don't need to do much interactive processing, I recommend ImageMagick. For a start, it has many different interpolation filters (specified using '-filter FILTER' commandline parameter) that you can try for image scaling, compared to GIMP's three. I'm certain that one of them will obtain better results for your particular situation.

Sven Neumann
2007-09-27 09:12:25 UTC (over 17 years ago)

scaling

Hi,

On Tue, 2007-09-25 at 17:01 +0930, David Gowers wrote:

So far as I can see, my Gimp (2.4.0-rc2) does have lanczos downscaling

I know. That is why I made a point of saying it doesn't. It has some strange facsimile of Lanczos downscaling. If you compare ImageMagick's implementation with GIMP's, you can see a clear difference (and that ImageMagick gives better looking results.)

Yes, the downscaling code, in particular the new Lanczos code, still has issues. Help with fixing that would be very much appreciated. If you want to help, and are able to help, please show up on the gimp-developer list.

Sven