Descreening

[Klaus Nordby]

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

[Wolfgang]

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

[Beth]

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

[Erik Heyninck]

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

[Beth]

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.

[mikeius]

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.

[Beth]

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

[Erik Heyninck]

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.

[Erik Heyninck]

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.

[Erik Heyninck]

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.