Hvis du skal scanne et trykt billede, enten fra en avis eller blad, så få du ofte striber eller et krydsmønster på skærmen.
Det er en slags interference støj mellem scannerens og skærmens billedfrekvens. Det kan afhjælpes ved at bruge Descreen under scanningen.
Når man først har det på billedet, er det svært at slippe af med det. Jeg har prøvet det med de mest avancerede filtre i både CorelPaint og Photoshop, men det bliver mere og mere sløret.
Se også disse hjælpesider fra AgfaSnapScanneren:
moiré
An undesirable visual pattern that appears in scanned images made from pre-printed (screened) originals.
Moiré can also occur in printing. In printing, it is usually caused by:
1. changing the size of halftone images in an application;
2. choosing incorrect halftone screen angles in process printing; or
3. misregistration of halftone screens in process printing.
Moiré patterns
Moiré patterns occur when your are scanning a pre-printed, screened original, or when a pattern in the original is being scanned at a resolution that is too low.
If your original is screened, avoid applying Sharpness to the image. Apply sharpness in your image editor, if necessary, or use a different Descreening value.
If you are using Descreen, and moiré patterns still appear, try scanning using different descreen values. Often a value that is a little lower or higher than the actual screen frequency of the original provides the best results.
Of course, whenever possible, avoid scanning screened originals. Use the original, unscreened image that the screened reproduction was made from.
To descreen a pre-printed, screened original
1 From the Descreen menu, choose the screen frequency of the original.
If you do not know the descreen value for your original, there are screen frequencies that are normally used for common materials.
To set a Descreen value that is not in the Descreen list
1 Choose Other from the Descreen list.
The Descreen-Other dialog will open.
2 Type the new Descreen value.
3 Click the OK button to close the Descreen-Other dialog.
FotoLook has now set the descreen value to the new value.
2 After scanning, inspect the image in your image editor to make sure that moiré patterns are no longer present.
3 If moiré patterns are still present in your image, rescan the image using a Descreen value that is above or below the one you used initially.
Rescan until the moiré patterns are no longer visible.
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