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Image resampling methods.
Old 05-03-2004, 11:12 PM   #1 (permalink)
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Hey all! I just posted a little article on my web site regarding enlarging photos. Check it out and let me know what you think!

Image Scaling Article Here.

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Re: Image resampling methods.
Old 05-04-2004, 04:52 AM   #2 (permalink)
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Resampling up in small increments does work. I have used this method several times with digital images that needed to be 200 to 400 percent larger and printed on an off-set press. Quality of the original image is important. There are limits to how far you can successfully enlarge, but it does work.

Tom
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Re: Image resampling methods.
Old 05-04-2004, 06:59 AM   #3 (permalink)
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Dave -

It looks good. However, your conclusion - that the default bicubic is the best method - is overstated. It looks the best for the type of image you were resizing. Other classes of resizing will give "best" results for other classes of images. I'm not savy enough to tell you which method will be best for which image, but the best method for an image with lots of sharply defined, contrasty detail may not be the best method for an image with primarily smooth gradiations in tone.

All in all, awesome enlargement. 10D - what lens? Would be interesting to try this with a resolution target. Maybe when I'm rich...
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Re: Image resampling methods.
Old 05-04-2004, 09:37 AM   #4 (permalink)
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Hey Guys,

FYI: You can download a limited use version of Genuine Fractals PrintPro 3.0 for Mac or Windows at:

http://www.lizardtech.com/download/d...ns.php?page=gf

It seems to produce results similar to upsizing in Photoshop.

Dave
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Re: Image resampling methods.
Old 05-04-2004, 03:12 PM   #5 (permalink)
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Hi Tom. When using the progressive technique, do you also do a standard one step re-size and then choose the one that looks best?

I admit, for my test I probably resized the image more than most people would need to. But from the results, I don't feel comfortable relying on the progressive technique as my only method for resizing, regardless of how much I'm doing. Besides, if the standard BiCubic method still has better detail than the progressive method after such a large jump, I think it would retain just that much more detail in smaller jumps.

For the next while you can bet that I'll be trying it out on several different images. If I see differences I'll put up pages to show those differences.

Thanks for the feedback!
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Re: Image resampling methods.
Old 05-04-2004, 03:16 PM   #6 (permalink)
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Hey John. Thanks for the feedback. I realize I may have overstated it but I feel it's with good cause. And I quote from the page;

"It is my personal opinion, at least in the case of my test image, that the best method for enlarging photos using the built in Photoshop tools, is to use the default BiCubic setting."

I will be testing this with several other images over the next while to see if there is a situation where it works best. Sports Illustrated tend to photograph a lot of people and this method may work well for those situations. I will post any further findings I encounter.

As for my lens (I should put this on there) It was the Canon 28 - 200 USM zoom. Not sure off hand what it was zoomed at.

Thanks for the feedback again! Cheers!
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Re: Image resampling methods.
Old 05-04-2004, 03:41 PM   #7 (permalink)
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Dave:

The way I have used resizing in the past is to enlarge the image by a small percentage. I don't remember the exact percentage I used, but 10% probably sounds about right. I then scale the image up again by this amount. I continue to do this until I reach the final size I need. As a default I use the BiCubic method.

Again, there are limits. A two megapixel image is not going to scale up very far without it showing signs of falling apart. A six megapixel image is going to have lots of rich details that will hold together through multiple scaling sets. The more information contained in an image the better it will respond to small steady increases in size.

It is important to do it as a TIFF or Photoshop format. You do not want any compression algorithms playing with your pixels. The best way to see how the progression is going is to keep an original copy and compare it at 100% of actual size to the upscaled copy viewed at 100%. How do the pixels in the same areas compare for sharpness, color, and contrast?

Tom
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Re: Image resampling methods.
Old 05-04-2004, 06:40 PM   #8 (permalink)
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Hey Tom, that's exactly what I had done here. I neglected to count the iterations so when I get home tonight I'll redo it and double check. I think I resized about 7 times before I reached my final 20 x 30. You can see in the tailight details that the progressive method has lost the details that have been retained by the simple, one-step BiCubic enlargement.

Simple BiCubic enlargement.


Progressive, 110% incremental BiCubic enlargement.
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