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Old Feb 1, 2006, 6:07 AM   #1
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I was just wondering what are the best settings to use in Photoshop usm for 8x10 prints or larger. All settings in my camera are set to normal, such as sharpness, contrast and saturation. I want to print high quality pictures without over sharpening and producing halos. Thank you.
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Old Feb 1, 2006, 10:36 PM   #2
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It's difficult to give good, general settings for USM due to the individuality of each image. That being said, Start with the Radius at 1 pixel and the Threshold at 0. With the preview window at 100%, drag inside the window to find the area of highest contrasting edges. Then, drag the Amount slider to the right until you begin seeing a white halo forming around the contrasting edges. Drag the slider to the left until the halo disappears, then back off a hair more.

If the image is rather "soft" with a lot of smooth areas that might suffer from being sharpened, then you start sliding the Threshold to the right a bit at a time until the soft areas remain soft.

Often, you can get away with sharpening a bit more than looks good in RGB mode if you apply the sharpening and then go to Edit > Fade Unsharp Mask and choose Luminosity as the blending mode. This only applies sharpening to the greyscale parts of the image and avoids color artifacts. A similar effect can be gotten by converting the image to LAB Color and applying USM only to the Lightness channel.

Some people use a formula to determine the Radius setting that depends on the resolution that you plan to print at: Radius = ppi divided by 200.

Products like Nik Sharpener Pro will do very precise sharpening using such variables
as print size and even average viewing distance.

Grant
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Old Feb 22, 2006, 6:44 PM   #3
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Hi Grant

Why do we have to sharpen for print anyway? Just sent my Fuji 9000 (9500 UK) back to Fuji because I wasn't happy with the images - they said camera is fine and that their algorithm 'blurs' on purpose so as not to overly affect the colour rendition! They said lab prints don't need sharpening because their equipment is sophisticated enough to sharpen images from digis automatically - inkjet printing is another matter however.

I'm used to Bronica and Nikons where everything is pin sharp so can't quite get my head around this new concept.
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Old Feb 23, 2006, 8:33 AM   #4
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John Morgan wrote:
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Hi Grant

Why do we have to sharpen for print anyway? Just sent my Fuji 9000 (9500 UK) back to Fuji because I wasn't happy with the images - they said camera is fine and that their algorithm 'blurs' on purpose so as not to overly affect the colour rendition! They said lab prints don't need sharpening because their equipment is sophisticated enough to sharpen images from digis automatically - inkjet printing is another matter however.

I'm used to Bronica and Nikons where everything is pin sharp so can't quite get my head around this new concept.
Getting a usable image out of a piece of silicon the size of your fingernail is a complex process.

You've got millions of invidual photosites that the light strikes via specialized microlenses to help amplify it. These photosites generate an analog signal based on the amount of light they receive, which is amplified based on ISO speed selection prior to the analog to digital converter which samples the signal from each photosite.

A Color Filter Array is over the photosites, allowing only one color to pass (red, green or blue) for each photosite, with twice as many photosites sensitive to green due to the way the human eye responds to light/color.

Then, demosaic algorithms look at adjacent pixels, combining the signals from photosites sensitive to either red, green or blue, to try and estimate the color for each individual pixel (even though the invidual photosite for a pixel is only sensitive to one color).

As a result of the way this process works, you can end up with color artifacts at transitions in color if the algorithms are not up to the task.

You can read about some differencesin algorithms in studies like this one:

http://www.ece.gatech.edu/research/labs/MCCL/pubs/dwnlds/bahadir05.pdf


Moire is also a consideration due to the way sensors respond, and usually require an Anti-Aliasing filter in front of the Color Filter Array. This filter does in fact tend to blur some of the details to prevent unwanted moire patterns.

In order to keep unwanted artifacts to a mininium, less sharpening is often applied in camera. Simplified, sharpening algorithms increase the amount of contrast you see at high contrast edges and transitions to give an illusion of more sharpness in images. If you apply too much in the camera, you can get unwanted halos around edges, etc. So, it's best to do this step using a high powered computer and software, versus the camera trying to get it "just right" in a split second between images.

Now, having said all of that, images from many Digital Cameras can be quite sharp, with lots of "real" versus perceived detail.

Are you sure that you weren't doing something wrong? For example, using shutter speeds that were too slow to prevent motion blur from subject movement or camera shake at the focal lengths you were using.

Often, a new owner of an "Ultra Zoom" model doesn't realize the impact of camera shake, which is magnified as more optical zoom is used, especially if they keep the camera set to lower ISO speeds.

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Old Feb 23, 2006, 4:47 PM   #5
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Thanks Jim, that has clarified things a lot (I had to read the technical bit twice, but got there in the end). I must admit I never realised that all that was going on in a 1/60 of a second.

I'll check out your other recommendations as soon as my camera gets back from Fuji.

Thanks very much for your time, John
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