# Best interpolating/upsizing method?



## elemental (Sep 9, 2009)

I'm going to be making a large print from a relatively small original (2592 x 2592 px crop from a D200 to a 36" x 36" print, or more exactly 54 4x6 prints that will be assembled into a 36x36- it's complicated but irrelevant). The actual resolution at that size is 72 dpi, which isn't exactly "high quality." I did a test print of a crop from the original at this resolution, and it does look good enough for the purpose, but I'd rather upsize it myself than let the machines at the print shop do it for me. I know there are different methods and algorithms to do this, so I'm wondering what has worked for people in the past. I have GIMP and Photoshop (and yeah, I prefer GIMP for most of what I do), and I'd be willing to try other software as long as it's free. It's really not worth going out and buying something for.

The picture, if you're interested:







I wanted something ghetto for my apartment, and this was (a) the right color range, (b) square and (c) had some hope of getting to 36 x 36 (sorry 35mm).


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## Garbz (Sep 9, 2009)

For upscaling I think GIMP's Lanczos filter is better than anything Photoshop has to offer, but then one thing that is critical here is that you have a lot of smooth gradients rather than fine detail. This means you probably won't notice a difference between Lanczos or Bicubic.

The last word in upscaling really is Genuine Fractals. This consistently provides far better large upscaling than anything else I've tried.


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## musicaleCA (Sep 9, 2009)

Garbz said:


> The last word in upscaling really is Genuine Fractals. This consistently provides far better large upscaling than anything else I've tried.



Ditto. Genuine Fractals is just...freaky. Fantastic, but to the point of being freaky. A comp sci friend of mine calls it black magic.


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## KmH (Sep 9, 2009)

Based on recommendations from Scott Kelby and Vincent Versace, the landscape photographer, I use Adobe's algorithm, Bicubic Sharper to upsize.


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## elemental (Sep 9, 2009)

Wow- based on the info gathered here and subsequent Googling, it sounds like Genuine Fractals really is the standard. Unfortunately, it's just not worth the price for this project. If I'm going to stay in the GIMP/PS realm, is it worth upsizing it myself or should I just send the files to Mpix at 72 dpi and let them handle it?


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## Dwig (Sep 10, 2009)

Here's an excellent series of comparisons between GF and PS:

The Online Photographer: It's Bigger, But Is It Better?

The Online Photographer: It's Bigger, But Is It Better? Part II

The Online Photographer: It's Bigger, But Is It Better? Part III

No one upsampling method is always the best. There are always trade-offs where one is better than another is some aspect but not the best when another attribute is considered. One this that is _always_ important is to do noise reduction carefully _before_ upsampling. Many upsampling methods can mistake noise for subject detail and try to create sharp edged "objects" out of a clump of noise.


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## Garbz (Sep 10, 2009)

Printers don't normally upsize. If you send them a 72ppi image you will get 72 pixels per inch, and from a meter away quite clearly see distinct small pixel squares.

It never hurts to upsize compared to printing standard. Fire up GIMP and up the res to 200ppi (should be way more than enough given the size of the final result)


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## Moglex (Sep 10, 2009)

Garbz said:


> Printers don't normally upsize. If you send them a 72ppi image you will get 72 pixels per inch, and from a meter away quite clearly see distinct small pixel squares.



This is absolutely true.

How would the printer know whether you were sending it a low resolution image or a post-pointilist image or some scientific visualisation?

I had a God almighty argument with Bifurcator and HelenB on this subject a while back since they both swore blind that the printer was responsible for upsizing.

(The exception is where the printer connect directly to the camera when it will know the provenance of image it's receiving and can thus make certain assumptions about it. Although whether it ever upsized would depend on the cropping selection criteria.)


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## KmH (Sep 10, 2009)

elemental said:


> Wow- based on the info gathered here and subsequent Googling, it sounds like Genuine Fractals really is the standard. Unfortunately, it's just not worth the price for this project. If I'm going to stay in the GIMP/PS realm, is it worth upsizing it myself or should I just send the files to Mpix at 72 dpi and let them handle it?


Mpix won't accept files at 75 ppi. They require a minimum of 100 ppi before they will print.

If you want an 8x10 it has to be at least 800x1000 pixels which is 100 ppi.

Here is Mpix's requirements.


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## skieur (Sep 10, 2009)

The best approach using Photoshop is to create an action which upscales the photo 10% and put it on a function key.  By upscaling 10% at a time, you will lose absolutely minimum quality even at 12 times the 10% action.

Try it.  It works.

skieur


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## Garbz (Sep 11, 2009)

Moglex said:


> I had a God almighty argument with Bifurcator and HelenB on this subject a while back since they both swore blind that the printer was responsible for upsizing.



Oh my god, I remember that. I remember having a really heated debate with you on some similar printing issue which resulted with you on my ignore list for like half a year. Times are a changing :hug::


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## elemental (Sep 11, 2009)

skieur said:


> The best approach using Photoshop is to create an action which upscales the photo 10% and put it on a function key.  By upscaling 10% at a time, you will lose absolutely minimum quality even at 12 times the 10% action.
> 
> Try it.  It works.
> 
> skieur



In my searching, I've heard this vehemently defended and flippantly discounted. The only way to know, of course, it to try it for myself. To give all of you an honest comparison as well, I'll upload 100% crops of both the one-shot upscale and the incremental upscale. Can you tell which is which?

A:







B:


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## Garbz (Sep 11, 2009)

I'm going to say B, the bottom one, the one with the detail preserved is the single upscale. 

Smaller increments in re-sampling fundamentally changes the way the resampling algorithms comes to the final solution. This is not the correct way to do it. Find an algorithm that works. Otherwise you end up clobbering your detail AND creating halos at the same time. Kind of akin to sharpening an image multiple times.


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## elemental (Sep 14, 2009)

Garbz said:


> I'm going to say B, the bottom one, the one with the detail preserved is the single upscale.
> 
> Smaller increments in re-sampling fundamentally changes the way the resampling algorithms comes to the final solution. This is not the correct way to do it. Find an algorithm that works. Otherwise you end up clobbering your detail AND creating halos at the same time. Kind of akin to sharpening an image multiple times.



Garbz is correct, and I absolutely agree that the single-shot upsize looks substantially better. The 10% version seems too soft and gives the impression of much poorer image quality despite substantially more data. I tried light sharpening, and this exacerbated the problem. In addition, the 10% version became ridiculously large- the final version was over 1GB. While there is more data in the file, it is clearly not data that is helpful for producing a quality upscale.

I'm sticking with the GIMP cubic in one-shot form. Thanks to all who offered input, and I hope my results might be helpful for others in the future.


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