Downsampling

[Pictus]

Most of time we resize the photos before posting in the forums, Flickr and etc...
But Photoshop do not have a good downsampling algorithm and I do not know any plug-in
that does a good downsampling, what we find are just upsampling ones.
Maybe Topaz can create a plug-in with Lanczos8 or better algorithm, it may be a good companion
to Topaz plug-ins as it creates an image with less artifacts, so a plug-in like Detail will have a cleaner image to start with.

Downsampling algorithm comparative Down sampling methods

Downsampling from 1000x1000 to 250x250 and oversharpened to easy show the artifacts
(The original image is in the link above)

[Albert Yang]

Hi Pictus,

Thanks for the info. I remember reading your other posting that advocate a better down-sampling. Lanczos algorithm is easy to implement.

However there is one issue. PS plug-in SDK don't allow plug-in change the image size. So you will see borders after downsampling and have to manually crop the the border out. So people may find it inconvenient.

Besides, I sort of feel that most people don't care too much for the down sampling quality since it does not show up much visually, is it the case?

[Pictus]

Hi Albert Yang,

Thanks for the response.
True, the common user do not care about this, just a few, the crazy pixelpeeper ones.
People also will not like another step to crop the image.

[daronk]

Besides, I sort of feel that most people don't care too much for the down sampling quality since it does not show up much visually, is it the case?

I use upsampling and downsampling routinely. It all depends on what size the client wants...I almost always have to do one or the other.

[Drazick]

I care about it.
You mentioned once that Upsamplig is one of your strengths.
I would really like to have a tool with this Algorithm (Both Downsampling and Upsampling).

[Pictus]

I bet CS5 still bicubic limited.

[Pictus]

CS5 is bicubic limited...

[Ed Weston]

The Lanczos filter is built into Irfanview and can be used for both up and down sampling.

[Pictus]

FastStone have Lanczos and ImageMagick *many* interesting algorithms, both free.
FastStone Image Viewer, Screen Capture, Photo Resizer ...
Resize or Scaling -- IM v6 Examples

Sadly Photoshop does not like ImageMagick JPG codec(look at the image below), who else does not too?
Resized to 25% from http://farm2.static.flickr.com/1084/...5912fe_o_d.jpg


Bicubic gives artifacts, Lanczos ringing at the edges, who will be the “savior” ?

To leave Photoshop to use another application is counterproductive.

[Drazick]

Albert, Any updates on this?