Descreening

[mikeius]

Placing the image in certain angles help to start eliminating moire since scanning.

Grayscale images should be placed in the scanner at 15 degree angle. Usually black is printed at 45 degrees.

Color images clear scenes should be placed at 45 degree. It help to preserve Cyan and Magenta that usually have more important information. As you said Yellow is not important, to soft.

Color images dark scenes also 15 degree angle. In this case black is more important than cyan and magenta.

Another important point is that image should be scanned at maximum optical resolution available in the scanner. This soft the scan. Printed images are to sharp. Also, Unsharp Mask should be avoided.

Regards

[emkaydist]

Eye Fidelity Tools...Plugin

[mikeius]

Depending on image scene you should place it at different angle when scanning. You can start descreening when you scan.

Grayscale images should be placed at 15 degree angle.

Clear color images at 45 degree

Dark color images at 15 degree

This way you start eliminating moire, while scanning, and you preserve more important plates colors and details.

Regards

[Kev Borg]

Hello Michael,

yes it is a pain but this is what i do.
if my final image is going to print and it works extremely well in most applications, mags, newspapers etc.

there are 3 to 4 steps generally
first i'll scan the image at a high res of 1200 dpi or as high as your scanner will go and load into PS6.
i keep the image as rgb until i have finished, this way i only have to edit 3 channels.

instead of playing with the whole image i use the channels and correct them, this way i get a better result. sometimes you can just use the same step on the whole image, it just depends on the severity of the moire effect.

BLUR - MEDIAN - UNSHARP

i start with the worst channel which is normally the blue channel.

i select the blue channel and then i select the Guassian Blur at a setting of around 2 to 5 depending how bad the moire effect is. normally around 2 most times.

then select the median filter at a setting of 1 to 3, 2 is normally okay for most images including digital photos when removing artifacts.

i do this on the red and green channels as well but alot of the time i use smaller settings in the blur and median filters as these channels are not normally as bad, and besides that it is best to keep one channel untouched if you can so that you can keep some of the detail in the edges.

after i have done all 3 channels (if required)
i go back the rgb main image and select the unsharp mask and use a setting of 100 to 300% and a pixel radius of the same as the blur i use. i never use the threshold in these cases.
eg: blur settings = 2 then unsharp setting will be 2. i use unsharp on the whole image most times.
don't go to high as the moire can come back.

If the image is really bad i will unsharp on each channel, carefully as you go though.

if i am happy with the final result i then resample my image back down to 300dpi. (by doing this you can sometimes get rid of most of the moire effect on its own without doing the other steps.)

after i have resampled down i then convert to cymk, then use level or curves to adjust highlight, midtones and shadows and if my colours have become a bit desaturated i will increase saturation by around 20 to 30, save file and send to the bureau.

make sure you use levels or curves before the saturation step.

i have created a set of actions for this so although it sounds like a lot of work the actions do all the work.

hope this helps

kev

ps, as you can see i am new to this forum and would like to praise all of you for an excellent site.

[This message was edited by Kev Borg on April 28, 2001 at 03:44 AM.]

[Klaus Nordby]

I've bought the $50 SilverFast LE now - it works great for descreening, and is a joy to use, with a lovely UI. Highly recommended!


K

[Erik Heyninck]

I sold my Snapscan and bought an Epson Perfection 1640 Photo. I downloaded Silverfast SE and compared the Epson software with Silverfast with a 4x5inch slide. I can't understand how it comes, but Silverfast gives visibly better scans.
As soon as I have the money, I'll buy it.
You are right: HIGHLY recommended.
The demo gives a rectangle in negative with the name silverfast in it when exporting to your software. I installed the twain version and it works OK in all the software that supports twain.

Thanks, E.

[mikeius]

If your method works for you Good!!! I respect it, but here is some opinions about your process.


BLUR - MEDIAN - UNSHARP

i start with the worst channel which is normally the blue channel.

i select the blue channel and then i select the Guassian Blur at a setting of around 2 to 5 depending how bad the moire effect is. normally around 2 most times.

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2 to 5 pixels Gaussian Blur destroy valuable information in your scanned printed image. Because when you blur any RGB channel, you are blurring color and detail together. It destroy moire, but also destroy valuable information.

For example if you have a girl face close-up. Some thin hair is running thru her face and background. When you blur, this thin hair will dissapear.

When you work in Lab, color is separated from detail. There you can work them independently, and you will be preserving detail while bluring color. You can't in RGB mode normally. You can trick it duplicating layer and merging it using layer Luminosity or Color modes.
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then select the median filter at a setting of 1 to 3, 2 is normally okay for most images including digital photos when removing artifacts.

i do this on the red and green channels as well but alot of the time i use smaller settings in the blur and median filters as these channels are not normally as bad, and besides that it is best to keep one channel untouched if you can so that you can keep some of the detail in the edges.

after i have done all 3 channels (if required)
i go back the rgb main image and select the unsharp mask and use a setting of 100 to 300% and a pixel radius of the same as the blur i use. i never use the threshold in these cases.
eg: blur settings = 2 then unsharp setting will be 2. i use unsharp on the whole image most times.
don't go to high as the moire can come back.


-------------------------------------------------

Under not circunstances you should apply Unsharp mask to all Channels at ones. When you apply Unsharp Mask it creates halos, and when applied to colors unwanted colored halos appears. I apply Unsharp Mask to Lightness, or Black and a weak channel in CMYK, in any case Magenta or Cyan. I never apply Unsharp Mask to Yellow. Another way is appliying Unsharp Mask to all channels, then Fade Last Command and selecting Luminosity merging mode. This way you only apply Unsharp Mask to Lightness even if image is not in Lab Mode. It let you apply heavy Unsharp Mask without compromising over sharping.

Another situation is that printed images are already to sharp, that is why you scan them at 1200 ppi. It soft the image. Of course with your method you need to Unsharp, because bluring destroy details. As you said, you can't sharp it much, because moire will comeback. Also, Unsharp Mask will not bring back details as thin hair.

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Hope it helps.

Regards