Descreening

Does anybody know of a good, **inexpensive** tool for sucessfully descreening scanned photos? Most annoyingly, Photoshop has no specialized filter for performing this important function.

Presently, I use combinations of Despeckle and Dust&Scratches. It sort of works, but it is cumbersome, for owing to all the screening variants of different scans no single Action can be made.

Thanks,


K

Yeah, I find that very annoying too!
A lot of my customers are only able to supply printed catalogues and so I have to descreen somehow all the time.

Usually, I scan the pictures at different resolutions, until I get a rather uniform screen. Those resolutions are usually rather high, 300++ dpi ..m according to the original size of the image.

Then I resize by 50% and maybe then 50% again. The moiré should be gone by now and I start sharpening, either with the Unsharp Mask, or with the excellent Kai's Equalizer.

For web-use, it gives pretty usable results, but still the way is a long one.

I would very much prefer a plugin or the likes ...

Wolfgang

Klaus, this is a tough problem. The best thing is to have scanning software deal with this at the scanning stage. I use AGFA fotolook and it works well as long as I know what the printing lpi is (usually 85, 133 or 150). ALthough this can be a trial and error type situation. (There is a tool that will measure screen angle and lpi).

But descreening software usually only comes with the mid to high range scanners. So if you are not lucky enough to have this, then you will have to do it in photoshop. And your despeckle and dust and scratches filter are the two tools that I would use to minimize the scanned pattern too. Using the blur tools sometimes works. I dont like the unsharp filter in this case as it can emphasize the halftone pattern and result in a worse problem than you started with.

Another trick is to scan the picture at a 15 degree angle (place the pic at 15 degrees on the scanner bed) and then rotate it back in photoshop. Ive done this and it seemed to work well.

The direct to plate printing industry uses copydot technology for this kind of thing. I have not seen this myself, but when you are ctp (computer to plate), you do not really want to deal with film coming in from advertisers etc. This is a big scanning station that scans at an incredibly high res in black and white mode.

I have done something similar to this copydot thing with my own scanner. I have only attempted this with course linescreens and only with greyscale (thus only on one plate). But it worked great. Scan in at a really high res like 2400 dpi in black and white mode. (the res should be what the dpi of the imagesetter will be). You dont want to resize or adjust this image in any way. Just use place the 1 bit image in your layout software. This way, there is no conflicting linescreens. What is output is just a series of black and white dots. If you need to do minor changes in size, do it in the scanning stage. But be aware that you are going to change the size of the dots. Going a little smaller may work....but when going bigger...be careful. Those dots are getting bigger too.

Beth

and I think it is a top/low budget scanner. It has an acceptable way of dealing with this problem when you scan as "magazine image". The scanner scans several times and reduces the moir

Erik, will fotolook work with that scanner. I thought it would work with pretty well all AGFA scanners...but I am not sure. If it does, I would try and get a copy. The control and versatility you get is really good. They do have it available on their website.

Attached a professional Remove Moire action.

Follow dialogs inside actions.

If you have any doubts, or you want to discuss this method, you can write to me directly or post here.

Enjoy it.

Michael, can you tell us what this does. Im using PS on a mac and I am not sure if all actions are cross platform or not.

Thanks,
Beth

I searched the Agfa site and couldn't find out where to download fotolook (not for PC, not for Mac). I noticed it accompanies the pro line of scanners, and I do believe yopu when you say it's very good, so I'm interested.

Beth, I searched the Agfa site and couldn't find out where to download fotolook (not for PC, not for Mac). I noticed it accompanies the pro line of scanners, and I do believe you when you say it's very good, so I'm interested.

was scanned as photo glossy on my Snapscan E50 from a postcard.
The following version was scanned as a magazine print with the same Scanwise software.
Probably not good enough for real professional work, but with a very little filtering it'll do for the web and home-work.

I keep reading really good things about a product called Silver Fast,its a third party scanning application,which apparently is, or alledgedly is the best out for being able to adjust your scans quite meticulously.

I assume they are at silverfast.com,and the company name is Laser Soft Imaging.


Stu. [img]/infopop/emoticons/icon_smile.gif[/img]

Thanks, I too have heard of Silver Fast but never seen their software. I now dowloaded the trial version for my Epson Perfection 1640 Photo scanner(a great scanner with so-so software), and Silver Fast is indeed very good at descreening - and much else besides! But it's $150 for my scanner - more than one third the price of my scanner. Still, it could be worth it. So I advise you others to check out Silver Fast - they have versions for just about all scanners, it seems, variying greatly in price.

K

Michael, I have downloaded your Action and shall try it now - thanks!


K

Klaus,I have an Epson 1240,and in the smart panel setup there is an option for setting up descreen for all scanning to remove moire.I asume you know this though? Although you can only use it for some image sizes,which is why you are looking for better software right?


Stu

I now see that there is also a Silver Fast SE - a smaller version - for just $49! I've tried the demo, and it's great! Check it out, if you need descreening and other advanced scanning functions for a reasonable price. I think I will buy it - once I somehow can get hold of $49. :-)


K

Stu, I've been using the Twain interface, since I HATE that kind of simple-minded, cute interface of Epson's Smart Panel. But I see you are right: it does have a highly limited, non-configurable descreeing function, and it works quite well. Good quality descreening, though the non-configurableness is annoying.

It will tide me over, until I get hold of $49 for buying SilverFast.

K

Phew, glad to see the forums still here. I had the forum page bookmarked and I kept getting server cant be found. With a momentary glint of wisdom, I checked talkgraphics.com. phew. Guess we changed addresses or IP's or something.

Erik, I went to AGFA's site and found the URL:
http://support.agfa.com/swPubDTP/

It looks like it will work with snapscan. There is a whole wack of snapscanners listed (I randomly checked a couple). I downloaded it too...Although I probably will never hook the scanner up to my windows machine again (but you never know). So if you cant find it, I can send it to you. Its around 4 megs.

I have read recently that noise in images can normally be found in the blue channel,and that about .5 of Gaussian blur cleans it up nicely,would this work for moire as well? if so you wouldnt have to worry about scanning on an angle etc anymore would you?


Stu.

Beth sorry for being late.

There is several things we should consider when eliminating moire.

1. Black is the Key in printing. It should be preserved.

2. Each plate is printed using different angles. We need to study the image to select how are we going to place it in the scanner to preserve particular colors.

3. We can blur colors independently of luminosity.

4. Automatically descreen filters and/or applications remove moire, but they destroy valuable information. They can't think, we do.

All these points are considered in my actions. This actions have dialogs with instructions. Follow them, or run the action step by step and you will see the process.

Regards

Thanks Michael

You know, I dont even know how the scanner software descreens. THe results are very good, but as you said, the results of doing it yourself can be better.

You mentioned screen angles and placement on the scanner bed. Does this mean that you scan in different inks at different angles. Or just use the black ink as the deciding factor regarding placement. Does it matter how the inks are printed...alot of press shops use KCMY. Dot gain would be the big think here...yellow being last as it is the least important. Oh, and would you scan in CMYK or RGB. I always scan in supersampled RGB for most everything.

Excellent tip about blurring colours independently of luminosity. (which for other folks means blurring the *a and *b channel in Lab colour mode.)

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

Eye Fidelity Tools...Plugin

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

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.]

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

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.

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.


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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