Re: Photoshop USM and CMYK conversion

[Glenn Barry <glenn@xxxxxxxxxxx>]

Try this, and the beauty of it is that if you don't like it then you can
easily go back and change it even after you have saved the file.

• Duplicate the layer that the image is on, if you have several layers already, copy each and then merge these copies to form one complete image layer.
• Duplicate this layer again and run unsharp mask on it, you can go really high on this 250% or more. the image will look grainy. As far as it goes images that look oversharpened on screen print well when printed from a press.
• Hit control F, or pull down the filters menu and select fade last filter, same difference.
• When fading the filter use the slider to change the percentage AND change the mode to luminosity. This gives the same effect as having used the unsharp mask on an image that was in LAB mode which is superior to sharpening in any of the other colour modes and doesn't create RGB or in your case CMYK noise.
• If you then save the result as a PSD File you later have the option of either deleting the layer or simply turning it off if you decide that you don't like the result that it has given.

For combinations of settings it is best to judge each image separately,
though you can easily write an action to facliitate things and still set
the USM for each image.

If you are going to press with these images it is a good idea if you contact your printer and obtain a profile for their press then use the Profile to Profile to conversion in the image mode menu. This is only available on PS 5 and later. If I were given the choice I would prefer to let the printer do this part as RGB to CMYK conversion is a huge minefield. If you are printing to an Inkjet of any flavour using anything other than a PS Rip leave the images in RGB as these are RGB devices, if you convert to CMYK, the standard driver converts back to RGB and then does its own conversion to CMYK. This loses colours and compresses the available Gamut of the printer.
There is another technique for sharpening images of dubious focus/sharpness that uses the HIGH Pass filter, but let me know if you would like to know that technique.

Let me know if you have any other questions.

Glenn

zxiong@xxxxxxxxxxxxxxxxxxxxxx wrote:

Hi,

I need to convert some 40 in images (at 300 dpi) to CMYK.  I scanned myself
with unsharp masking turned off because of excessive stitching and retouching.
I wonder if there are any rules of thumb using USM in photoshop for images
of given sizes.  I found an amount of 150 % with a radius of 3 pixels at a
threshhold of 5 to 10 seemed to be fine.  I'd like to make sure if this is
the best combination before I would regret. Lowering the threshhold would mess
up the sky.  Or would it be better to sharpen different parts of the images
separately?   Any help would be greatly appreciated.

Zonghou Xiong

--
Glenn Barry Photography
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