Interpolation Article

[Ron Bigelow]

I have just posted an article on interpolation. The article can be found on my web at:

http://ronbigelow.com/articles/interpolation/interpolation.htm

Other articles can be found at:

http://ronbigelow.com/articles/articles.htm

Ron Bigelow
http://ronbigelow.com

 

[woffles]

Will the rest of the article have the actual steps involved in doing a stair step in PS? I've never done one and would like to see it step by step.

 

[Ron Bigelow]

The article will not cover the actual steps. It is fairly simple; just do a Bicubic interpolation at 110%. Then, keep repeating the process until you get to the desired size.

Ron
ronbigelow.com

 

[MK914]

Love learning new things! Always do with your articles.

 

[fabgo]

--
Fabian

 

[Sven Hedlund]

You are a good writer Ron! Now please finish the sharpening series! ;-)

Best regards,

--
Sven Hedlund

http://www.svenhedlund.com

 

[Mike Worley]

. . . and the example images are particularly useful!

Thanks again,

Mike

 

[sting]

Great article. I really enjoy seeing the examples of various interpolation algorithms , although it would be easier to compare them if smaller segments were set side-by-side.

I would like to mention that interpolation isn't anti-aliasing, as shown in figure 5. Anti-aliasing is (usually) the reduction of higher-frequency data before the data rate is reduced, as in using an analog brick-wall filter before sampling or using a digital low-pass filter on digital data before sampling rate reduction. So, smoothing a sharp edge with is not anti-aliasing. You can't undo aliasing (undersampled data) by smoothing.
Once the data is aliased, it can not bu "un-aliased" .

Video game chip manufacturers (nVidia, ATI, etc.) tout anti-aliased performance, but they are really reducing larger data sets to fit on the screen pixels. That is why anti-aliasing by 2x or 4x seriously reduces the frame rate.

 

[Dao Dang]

your articles are very helpful to me. Keeps the good work!!
--
Dao Dang
Learning, still learning!!
http://www.pbase.com/daliakin

 

[Evan Effa]

Thanks for highlighting this interesting issue

It would be worth noting that Qimage has a different approach using Lanczos interpolation or Pyramid interpolation. It has the advantage of applying the interpolation for each print job on the fly with maximized quality...it works very well & keeps one from having to do all this manually as when you print form Photoshop.

Here is a link from the Qimage site that outlines this:

http://www.ddisoftware.com/qimage/quality/

-evan

--
Fuji S2 etc.

http://www.pbase.com/eheffa

 

[Mr. Jalapeno]

...with PS Bicubic Smoother/Sharper interpolation algorithms, according to PS creator Thomas Knoll and Chris Cox, who is the fellow from Adobe who created these latest interpolation algorithms. In fact, they maintain that using 10% stairstep resampling with Smoother/Sharper may result in worse quality in most cases.

Thomas Knoll's reply:
http://www.adobeforums.com/cgi-bin/[email protected]@.3bba34a3/3

Katrin Eismann:

"For my general interpolation setting I choose Bicubic and when I am scaling images up or down I select the best interpolation for the task at hand - smooth for upsizing and sharp for downsizing images. In the past some photographers used the ‘Step Up’ method made popular by Fred Miranda to size images up in 10% increments. With the new interpolation schemes there is no need to go through this slow process any longer."

 

[nicola]

Perhaps the correct old saying is "The Proof of Pudding is in the Eating"!?!?

)

--
Nicola (mr)
(Amateur Photographer)
http://www.pbase.com/nicola/galleries

 

[Ben Gamble]

Ron:

Just to clear up a bit of confusion I have. In you initial examples, you discuss a 200% increase. I believe that you doubled the pixels in each axis, thus increasing the total pixel count of the image by 400% -- correct?

I've previously heard that referred to as a 400% increase, whereas a 200% increase would have increased length and width each by 1.414X -- netting a total pixel increase of 200%.

I don't know which nomenclature is more correct, I just wanted to make sure that I understood your examples. Thanks for the articles! I've read nearly every one.

Merry Christmas & best regards,
--
bg

 

[sting]

I always wondered about stair-step interpolation. It's basically the same as applying a heavier low pass filter during interpolation that that available with a spline. There should be more halos (filter ring) than with a single interpolation, which would be better for some types of images and horrible for sharp edges.