Scanning with the DeScreen option

[Kampar]

Printed materials, such as DVD and Bluray covers, magazines etc. often use a specific technique called 'Halftone' to put the colours on the paper during the printing process. Historically, Halftone images were prepared using 'screens' although nowadays the methods used are more modern.

When you scan a halftone image, the resolution of the scanner can often cause strange patterns to appear in the scanner output. We call this patterning 'moiré'. The type of moiré that results from a scan can differ based on the scanner model and the image being scanned, even sometimes from the orientation of the image on the scanner bed.

The images below show 3 common types of moiré from 3 different scans.

The first image shows a 'checkerboard' effect where there are thin horizontal and vertical lines over the image. The second shows diagonal purple tinted lines running down the image. The third shows a grainy, pixellated image - sometimes these last types of patterns look like small, repeated 'rosettes' all over the image.



If you are planning on uploading a scanned cover and see any of these types of moiré in your original scan, it's unlikely that your final image will be good enough to be approved on the site. To get rid of moiré like this, there are several tricks you can perform, but almost certainly they will degrade the image to the point where it is no longer good enough to use.

So what to do?

Fortunately, the people that make scanners realized this problem a long time ago. Most scanners have the ability to compensate during the scan of halftone-printed material and this is done by enabling the DeScreen option in your printer software (DeScreen 'undoes' the screen printed halftone process). If you turn on DeScreen and then perform a new scan, the difference (especially if you are using a good flatbed scanner) can be quite remarkable.

The image below is from the same scanner as that shown above. The only difference is that DeScreen has been enabled in the scanner software for the scan.



This image is good enough to then take and turn into a proper scanned cover upload.

Don't despair if you do not see an option for 'DeScreen' in your scanner software. Sometimes the option is presented as a selection of either 'Photo' or 'Magazine' - you need to select 'Magazine' which represents all printed materials (real photographic images are not printed in the same way so you should never use DeScreen when scanning a traditionally printed photo).

You may notice that the scan done with DeScreen is a little less sharp than the non-DeScreened version. This can be corrected easily in your graphics package using a simple unsharp mask filter. It will look significantly better than a scan done without Descreen that then has some other correction applied to it.

Depending on how good the scanner hardware is and what you are scanning, you may still see some residual moiré in the image. If necessary, this can be further removed using several techniques ... search for 'moire' on this site to find several free tutorials for how to do this.