Digital BW, The Print

Hi,

As I understand it, the maths behind GF is published but patented 
(rather than a trade secret)..

I compared GF and most of the other available methods practically 
several years ago. At the time almost anything was an improvement on the 
standard Photoshop bicubic for most images.  Many programmes have a 
decent version of the Lanczos method that is almost always better than 
both GF and bicubic for upsizing photos.

However I found that the best and most convenient method for upsizing 
batches of images was to use QImage, which will of course output tiff 
files. It does implement other methods, but I found their 'pyramid' 
method gives excellent results and so use that.

Regards,

Peter

Peter Marshall
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and elsewhere......



Jeff Medkeff wrote:

>John Moody wrote:
>
>
>  
>
>>We sound like a broken record here but...  Qimage..excellent.  CS2 is pretty
>>good as well assuming you are not trying to scale too excessively.
>>    
>>
>
>Since I have a few minutes free, John's comment seems like a good 
>opportunity to talk a little more about splines....
>
>What spline(s) does Qimage implement? According to the website, they 
>support "Lanczos, Vector, and Pyramid" interpolation. Are these the only 
>three? I understand 'vector' and 'pyramid' to be spline classes, which 
>makes it hard to understand exactly what Qimage is claiming. There are 
>good and bad pyramid splines (when it comes to applying them to images, 
>at least), and I expect the same is true of vector splines. Lanczos, 
>however, is a specific way to compute the spline, and it is quite good 
>with a typical photographic image and doesn't do at all poorly on 
>graphics designs with lots of smooth lines, either. I'm also a little 
>unclear on whether Qimage will allow you to open a TIFF, compute its 
>spline, and save it back as a TIFF for more work in Photoshop, or 
>whether it is a print output tool only.
>
>Photoshop is strictly 18th and 19th century in terms of its spline 
>support. And I mean that quite literally - the math behind all three of 
>their methods is at minimum well over a century out of date. The three 
>methods are bicubic, bilinear, and nearest neighbor. Bicubic is an 
>excellent way to undersample, but is a rather problematical algorithm 
>for oversampling - more on this in a moment. Bilinear is something of a 
>special-case spline, not usually appropriate for upsampling photographs. 
>And nearest neighbor is a blunt instrument that I think I independently 
>invented when I was 16 for interpolating values from Cepheid light 
>curves on an Atari 400 in CPM/BASIC. It is possible this spline was 
>invented prior to the year 1500. You don't want to go there. Photoshop 
>is in pretty serious need of spline improvement.
>
>I think it is still true that Genuine Fractals is proprietary (hence my 
>previous reference to "mystery math"). If so, nobody really knows what 
>it does. I do agree with another poster that GF is almost always better 
>than bicubic for oversampling, especially at certain ratios where 
>bicubic tends to resonate.
>
>Photozoom Pro supports the S-spline, Lanczos, Hermite, Bell, Mitchell, 
>Catmull-Rom, B, Nearest-Neighbor, Bicubic, and Bilinear splines. I can't 
>say my experience is extensive with most of these.
>
>Part of the "problem" with some splines is that they are either patented 
>(for example, S and B) and rarely or never licensed, or they are trade 
>secrets (for example, Genuine Fractals). Also, spline computation is a 
>very fast-moving area of math these days. All this accounts for the 
>fragmentation of the spline market and the reason there are a dozen 
>tools out there. However, the patents also mean you can go read all 
>about the method, sometimes including the math.
>
>S spline is particularly interesting in this respect. It avoids aliasing 
>entirely, as far as I can tell (actually, I think it would alias at 
>ridiculously high frequency proportions, well beyond what would ever be 
>encountered in real life). The technique does not make any changes to 
>the proportional tonality of the image (some other interpolations, but 
>by no means all, do). It almost fully preserves, but does not enhance, 
>acutance (this avoids the excessive shadowing along tonal boundaries, 
>similar to overusing USM, that some splines introduce). Mathematically, 
>the image coming out of s spline has bulk properties (acutance, edge 
>sharpness, histogram) nearly identical to the original.
>
> From my experience with it, I think the S spline is currently the gold 
>standard against which all other methods of computing a spline should be 
>compared. It can be used pretty effectively at any point in the 
>workflow, including (I believe, somewhat heretically) being applied 
>after sharpening if you are using something other than USM. In the 
>spirit of making a meaningful comparison to S, I'll say:
>
>Lanczos: comes fairly close to S, tending to introduce certain artifacts 
>on medium-contrast boundaries but doing very well with sharp graphic 
>design edges and not bad at all on most photographs. Does not preserve 
>image acutance as well as S, but it is a small difference. If you have a 
>tool that does Lanczos, you probably don't need to move to a tool that 
>has S.
>
>Genuine Fractals: notably inferior to S based on my experiences a few 
>years back. It fails to preserve acutance as well as S or Lanczos, and 
>bulk tonality changes can result in images with multiple high contrast 
>boundaries. However, it is far better than Bicubic.
>
>Bicubic: really, really stinks compared to S, Lanczos, and GF. It 
>aliases, resonates, and introduces several different kinds of artifacts 
>including one which appears similar to noise, and another which is 
>similar to a ghost image of brightly toned image elements. It also fails 
>to preserve image acutance, doing far worse than GF in this respect.
>
>I'd be curious to hear what people have thought about Lanczos or GF in 
>comparison to algorithms such as Qimage's Pyramid and Vector, and the 
>T-spline (if anyone is using it). Also, I'm perfectly open to being told 
>my impressions of the four splines above are wrong - there are some 
>unavoidable mathematical *facts* about all of them, and I really like 
>dealing in facts; but their application is aesthetic in this context, 
>and that makes all the difference. I'm not married to my spline by any 
>means.
>
>  
>