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Old Sep 29, 2006, 12:49 PM   #1
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i have an opportunity to sell a number of images through a local gallery, but the owner wants large prints (18x24 or larger, preferably 24x36) to display. i have a Canon 30D, 8.2Mp - how large can i go with interpolation using this camera, before image quality suffers visibly? what's the best interpolation software to use for maximum clarity and image quality at sizes up to 24x36?
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Old Sep 30, 2006, 2:59 PM   #2
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First I think you should easily be able to do this. Of course they wont have the quality of a medium or large format but should be quite good. You could have them printed by somewhere that uses their own interpolation to size the print up. You can also use your own interpolation and just print a small crop of the correct upsizing to check it out. I use either PrintPro4 or Alienskin Blowup. You could use the interpolating up in 10% increments too. Using low iso and correct exposure for your original will help the quality too
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Old Oct 1, 2006, 12:49 AM   #3
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Some knowledgable people on this forum have said that Qimage has the best interpolation algorithms out there. Good results can be obtained in Photoshop using the "stepped interpolation" method that sasc mentioned -- blowing it up in steps of 10% or less rather than shooting for the target size straight off. People who do that a lot usually end up making an action out of it so that hitting a certain hot key will run the action on the currently open document and do a 110% (105%, whatever...) increase.

What might help you is to know the proposed average viewing distance from the prints. Then you could better judge the quality of your test prints. What sasc said about blowing the pic up and then cropping out an area of high detail to print will let you see the level of quality of the entire print without wasting ink and paper on full-sized test prints.

If you think that this sale could open doors for you, it might be worth while to farm this out to a professional printmaker if the costs are reasonable.

Grant
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Old Oct 3, 2006, 9:45 AM   #4
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thanks, guys. i don't print these sizes myself, that's for sure!

style="BACKGROUND-COLOR: #000000"the average viewing distance is really not something i can find out, since the prints i sell will be placed in people's homes, and i don't know where they'll put them. i can only assume that they will be viewed from some distance greater than arm's length (the "normal" viewing distance for prints is generally considered to be twice the diagonal length of the print). for a 20x30 print, i'd expect it will be in the neighborhood of 5-6 feet at least. i got some large prints back yesterday, and at that distance, they look very good. even at arm's length, much closer than most would stand to view a 20x30 image, they look quite nice. much closer, though, and the softness in detail starts to become apparent.

style="BACKGROUND-COLOR: #000000"what i'm really concerned about is sizes even larger than 20x30. the owner of the shop that will be selling them for me wants one for her dining room, as large as she can get. i can probably get to 24x36 with a little more work, but i'm not sure if i can push an 8Mp image up to 34x44, much less 44c-x66, using ANY interpolation software!

style="BACKGROUND-COLOR: #000000"i'll look into Qimage... i hadn't heard of that one. have either of you tried Genuine Fractals? i've heard good things about that as well...

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Old Oct 4, 2006, 1:48 AM   #5
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Genuine Fractals is supposed to be pretty good, but I can't say whether it does a better job than Qimage. There might be a website out there that has made such comparisons.

For the really big prints, you might have to do something drastic -- like have a big master print scanned with a high-rez scanner that will provide the high pixel count you need for a cleaner enlargement, or have the large master print photographed with a medium-format digital or a medium-format film camera and then get a high-rez scan of the negetive with a film or drum scanner.

Don't know whether the selling price would be worth the additional outlay for the drastic approaches, but it might be your best bet for clean, BIG prints.

Grant
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Old Oct 4, 2006, 6:09 PM   #6
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anyone heard of a program called "Imagener"?

i got some 20x30 prints back the other day, they looked really nice, now my client wants one at 30x40... i guess i'll find out just how far an 8Mp image file can be upsized before it starts to look crappy... :G
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Old Oct 7, 2006, 8:28 PM   #7
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Hey, Squirl, check this out: http://www.alienskin.com/blowup/index.html

It's a new program claimed (by the creators) to be the best there is at major interpolation.

Grant
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Old Oct 9, 2006, 12:15 AM   #8
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i downloaded the Alienskin "Blowup" plugin and tried it with a photo i took last summer. so far, i am NOT impressed... here are samples. the first was upsized from 800x613 to 2000x1533 using Irfanview (B-spline filter); the second was upsized in PS 7.0 using the "Blowup" plugin, also to 2000x1533. i then cropped the same portion of each photo to produce a "postable" sample... as you can see, the Irfanview sample is pretty rough, and the edges are indistinct. but the Blowup sample, while it has smoother, sharper edges, also exhibits a "wormy" look that seems to affect any part of the imageexcept those withoutnoticeable texture... the last pic is the original 800x613 file i used to do the test. all i can say at this point is that i'm very glad i tested the demo version before i spent $200 on this!!!






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Old Oct 9, 2006, 11:01 AM   #9
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i contacted Alienskin about the wierd artifacts in the enlarged image, and this was the response from one of their tech support guys...

"This is a limitation of the Blow Up algorithm. For fine, noisydetails - like the texture of the rocks - Blow Up averages the areas intotriangles and scales them up. The only way to improve the quality ofthe output would be to start with a larger image or not scale it asmuch. Obviously, this is not always an option, and making those changeswill help any scaling algorithm look better. For images withhighcontrast, low texture areas, Blow Up does a fantastic job. If the customerisn't satisfied with Blow Up, we can issue him a refund."



in other words, Blow Up doesn't work well with images that have lots of texture, and that require enlarging beyond 1.5-2x max. since some of my clients want prints up to 30x40", even starting with a full-size8mp file from my 30D would require me to enlarge the image beyond Blow Up's capabilities...



it's a bit sad that i can get better results with Irfanview, which is FREE, than with Blow Up, which costs $200!!
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Old Oct 9, 2006, 11:04 PM   #10
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Major bummer. The Blowup blow-up looks like it went through the Photoshop Plastic Wrap filter.

Sounds like the program might work better for graphic art than photographs. Viva la free demos!

You tried Qimage yet? I think that's only $45.00 or so. Free demo?

Grant
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