Sharpening Question

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Posted By
GordonGraham
May 13, 2005
Views
397
Replies
9
Status
Closed
I have recently started using the sharpening techniques outlined by Jeff Schewe in his article "Image Sharpening – Make it Really Sharp" (there’s a link to it on the pixelgenius.com site).

In the output sharpening section he indicates that the image must first be sized to the final output dimensions and resolution before applying the high pass/USM combo sharpening steps.

I’m an amateur and most of my output is to my ink jet printer. I often make different sized prints, ranging from 4×6 to 13×19, from the same image file. I usually don’t resample the image file to make a different sized print. Instead I just change the size using the Image>Image Size … dialogue. Of course the resolution is different for each different image size, but the pixels are exactly the same.

Since the pixels don’t change, is there any reason to "size" the image before applying the output sharpening steps? If the image is going to be printed at a couple of different sizes, is there any need to use different amounts of output sharpening for the different sizes?

A last question is whether there is any benefit to resampling the image for different size images rather than handling it the way I do.

Thanks for any help!

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chrisjbirchall
May 13, 2005
Whichever way you look at it, your image is being resized. It stands to reason that Photoshop will do a whole better job of it than the printer software. Whether you will actually be able to see any difference, however, is a different matter altogether.

Why do try a quick comparison by printing the same image using both methods?

Chris.
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YrbkMgr
May 13, 2005
I think the point Jeff is making stems from the notion that if you sharpen and then resize, you diminish the effects of the sharpening. It is often discussed here that in general, it is better to apply sharpening on the final output size/resolution of the image.

So to your question about different sizes and amounts of sharpening, in theory, yes, they would require different amounts to have the same or nearly the same effect. But as Chris mentions, whether you can see a difference is highly subjective.
JJ
John Joslin
May 13, 2005
it is better to apply sharpening on the final output size/resolution of the image.

In fact Bruce Fraser recommends doing it at three different points in the workflow!

See <http://www.creativepro.com/story/feature/20357-1.html>
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GordonGraham
May 13, 2005
I am actually using the three step method that both Bruce and Jeff have recommended in very slightly different ways. It’s the final output sharpening step that I’m confused about.

My confusion here is that if I simply size the image without resampling, the number of pixels doesn’t change. So I can sharpen it once, size it to, say, 4×6 and send it to the printer. Then I can size it to say, 8×12 (just to make the numbers easy) and send it to the printer again. In both cases, the same exact pixels are sent to the printer, sharpened exactly the same.

On the other hand, if I size and resample to 4×6 with a resolution of, say, 300 dpi and also do a size and resample to 8×12 at 300 dpi, then I’m generating two completely different sets of pixels. In this case, it makes complete sense to me that you may want to sharpen them differently. But I can’t convince myself that it would make any difference if I don’t resample.

Chris — are you saying that I should resample for each print size? That would, in effect, throw away some image data for smaller prints wouldn’t it? If so, what resolution would you recommend?

I appreciate the help!
Gordon
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chrisjbirchall
May 13, 2005
My confusion here is that if I simply size the image without resampling, the number of pixels doesn’t change.

But they do. In sending the image to the printer, the image pixels at, in your example, 300 ppi (pixels per inch) are interperated into drops of ink at a given dpi (dots per inch).

Now all of what I’m about to explain is probably purely academic, only doing a live test on your images on your printer will prove whether there is any benefit either way.

Let’s say your printer is a six ink 1440 dpi model. That means it can lay down 1440 dots of ink per inch. The printer software tells each jet how much ink to squirt for each of the six colours based upon the value of each single image pixel. Therefore to exactly match the printer’s dots per inch to the images pixels per inch, we need to divide 1440 by 6.

This means that (in theory) by sending a 240 ppi image to your 1440 dpi printer no interpolation of the image will take place in the printer software. I say in theory because some printers will adjust the image size slightly to accommodate full bleed (edge to edge) printing to ensure no white borders appear due to slightly misaligned paper.

Okay, so we’ve ascertained that the optimum ppi to send to this particular printer is 240ppi. It would make sense therefore to resize the image in Photoshop (using Bicubic Sharper to reduce and Bicubic Smoother to increase) to the final print size at 240ppi.

So – to answer your original question: As resizing an image can affect the sharpness (both up and downsizing) it follows that best practice is to sharpen after resizing for each different size.

Will you notice a difference? Maybe if you run a comparison test and hold the prints side by side and really "sniff" them.

Is it worth the hassle? Only you can decide.

Hope this has made the concept – if not the actual print – clearer. <grin>

Stay sharp.

Chris.
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deebs
May 13, 2005
FWIW & IMHO there are local solutions and there are general solutions.

This falls into the local solutions grouping as tyhe perception upon which the result is based is not a standard or technical test but one’s own perception.

I’d be tempted to:
1 – choose 2 distinct images, say, one with complexity (trees in leaf, s busy sky and detail on tree bark) and one with bland bits (sky, sea & sand)

2 – create a log and use several different approaches as recommeded by the Photoshop gurus and maybe a couple of variants of your own choice.

3 – do the straight forward practical and pragmatic comparison as defined by one’s own perception

FWIW I’d make most adjustments at 100% zoom to aid fine-tuning
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GordonGraham
May 13, 2005
Hi Chris,

Thanks so much for all your help. Your last post cleared a lot of things up for me. I’m using a Canon i9900 printer. From what I’ve been able to gather, if I resample, 300 dpi would probably be a good choice for it. They have an advertised resolution of 4800×1200.

It seems there are three points for me:

* If I choose not to resample, I can just do the output sharpening once and then resize to any print size. Within Photoshop, if I use, say, 100% zoom to tune the sharpening, I see exactly the same image and exactly the same pixels regardless of the Image>Image Size … setting (again, no resampling). Hence, any size setting would lead me to choose the same sharpening setting.

* If I do choose to resample, then I should resize/resample/output sharpen independently for each different print size.

* The choice as to whether to resample or not should be based on doing some tests and seeing whether I can tell the difference in the prints.

Does this sound right to you?

Again, thanks.

Gordon
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chrisjbirchall
May 14, 2005
The choice as to whether to resample or not should be based on doing some tests and seeing whether I can tell the difference in the prints.

Does this sound right to you?

Again, thanks.

Glad to help Gordon. When I ran similar tests on my own machine any differences were barely perceptible.

Best of luck with it.

Chris
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deebs
May 14, 2005
Unless there are gross differences personally I believe the distinctions in a ‘blind’ test would be hard to spot.

On the other hand, once options have been selected try a print out of each at, say, 10" by 15" as part of the research.

Then possibly select a common area crop and try that at a maxed print out too.

Not all image viewers show stuff the same way – for example try Paint.NET beta

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