Sharpening digital camera images for photo-store printing

From: “Mike Russell” <geigy@pacbell.net>
Newsgroups: rec.photo.digital,alt.graphics.photoshop,comp.graphics.apps.photoshop
Sent: 29 August 2003 00:50
Subject: Re: Sharpening digital camera images for photo-store printing

Matti Haven wrote:
> My very first Olympus mju/Stulus 300 6x4” (15x10cm) glossy prints at a
> local store were surprisingly good. I did a very basic tonal and color
> correction with Levels and minimal cropping (mainly to convert them to
> 3:2 aspect ratio).

> What about sharpening the images before printing at a store?

Nothing wrong with this, though my guess is they are doing some sharpening already, and your images will look fine out of the camera for 6x4. You will probably see the most improvement setting the correct shadow and highlight value, and removing any color cast with - you guessed it - curves.

> I guess it is best to set the digital camera to highest jpg quality to
> avoid the jpg artifacts which sharpening exaggerates, right?

Again, this is true for larger prints, but not an issue for 6x4

> But at least my camera tends to have noise which even a mild Unsharp
> Mask makes ugly very quickly so should somehow blur the images before
> sharpening?

Yes, do both, but sharpen to gain detail, and blur to remove chroma noise as follows: Convert your image to Lab mode, and blur the a and b channels to remove chroma noise. You may be fairly agressive with sharpening the L channel, since there will be no color fringing. Then blur the a and b channels slightly - radius 1.5 or 2. Convert back to RGB of course, before sending your images to be printed.

You may also get interesting results converting to CMYK with light GCR and sharpening the K channel only.

> An old source recommends the following action for digital camera
> images: New Layer, Filter/Noise/Median 2 (or even 3),
> Filter/Blur/Gaussian Blur 1, Filter/Sharpen/Unsharp Mask 500/1/0,
> Layer Opacity to 30-50%, Layer/Merge Down. Then just before printing
> Unsharp Mask 200/1/0.

My guess is these settings were designed for a lower rez, noisier technology than your camera provides.

> Some sources recommend Unsharp Mask 250/0.6/0 for detailed images and
> 70/2.7/4 for soft images. Is this a good amount for Photo-store
> printing or is this for halftone printers? And is it a good idea to
> somehow blur the image first?

I would not recommend blurring before sharpening for a photograph.

Mike Russell
http://www.curvemeister.com
http://www.zocalo.net/~mgr
http://geigy.2y.net

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