Checkerboard pattern in scanned picture
KarenR7
I am brand new to the wonderful world of scanners. I just bought a Mustek
scanner, which I will mostly use for text, but for fun I scanned a colorful
picture from a magazine. Different sections/colors of the scan have a
checkerboard or stippled effect. What is this called, what causes it and how
can I get rid of it?
Dennis Isenberg
There should be a Descreen option somewhere in the scanning software.
You need to try different settings in it.
Dennis Isenberg
KarenR7 wrote in message <19971223191...@ladder01.news.aol.com>...
KarenR7
Thanks to all who responded to my query. I will study the scanner website.
Karen
hlee
checkerboard pattern in scanned magazine pictures:
hi karen .. the checkerboard pattern is the magnified dither pattern
used to print news paper and magazines. both get shades of gray by
using dot patterns .. if you scan at a dpi (dots per inch) setting that
isn't greater than the pattern on the print then you miss some dots and
catch others.. a large pattern develops in your scanned image (checker
board).. if you know the interval of pattern on the print then you can
scan at greater than that interval ... there is a standard range for
news papers & magazines .. it is different for each media ..you have to
scan at at least 1.5 times the interval or 2 times if you want best
results so that you don't miss any dots .. the interval for each media
is listed below
news paper 85 lpi (lines per inch) scan at 130 dpi to abt 170 dpi
magazines are usually 133 to 150 dpi scan at 200 dpi to 300 dpi
fine art magazines can be as high as 200 to 300 lpi multiply this by
1.5 or 2 for your best scan dpi
what i do is scan the picture at hi resolution like 300 dpi (to make
sure you don't miss any dots) then run a smoothing filter (usually
available in photo program) then reduce the picture down to the
resolution and size you really wanted i.e. 75 dpi ... then i run
unsharp mask filter (sharpens picture) and do other processing
(brightness, contrast, gamma, tonal adjustments etc.) ..if your picture
is very big it pays to have a lot of memory otherwise the system slows
down a lot .. i use at least 32 meg ram ..some scanner software like the
ADARA (nice scanner, nice software) include processing called
descreening for this purpose... you are going to love your new scanner
karen .. good luck harry
sho...@ibm.net
>I am brand new to the wonderful world of scanners. I just bought a
>Mustek scanner, which I will mostly use for text, but for fun I scanned
>a colorful picture from a magazine. Different sections/colors of the
>scan have a checkerboard or stippled effect. What is this called, what
>causes it and how can I get rid of it?
It's called moiré (accent over the e). It is a pattern caused by the
interference of scan dpi with the halftone dots used to print color and
gray scale in magazines and most other printed material. Best way to
eliminate it is at scan time using a descreen filter, if your scan
software has this function. If not, try scanning at higher dpi and
resample down to desired resolution. Also suggested after scanning at
higher dpi is blurring the image, resampling dowm, then sharpening.
For some more info see item 6 in Wayne Fulton's scan basics pages
http://www.cyberramp.net/~fulton/scans.html#menu
And for an intro to halftones and screening