scanner comes with its own software that is used for operating the scanner. Each
software program is slightly different but works basically the same as others. Some include drivers
that are used with Photoshop® so that the image can be scanned directly into
Descreen: Most scanning programs have a feature called "Descreen".
In theory, the descreening feature is supposed to blur or merge dot patterns
into a solid set of pixels. In reality, descreening softens and distorts
the artwork, avoiding
moiré patterns. When you choose descreen in your software,
you have a choice of which line screen was used to print the original image,
usually 175 lpi, 133 lpi, and 85 lpi. The lower the linescreen amount you
choose, the higher amount the blur will be.
of a previously printed item
of a previously printed item
Masking: "Unsharp Masking" is an increase of tonal contrast in the areas where light and dark tones
come together. This increased contrast gives the appearance of a sharper picture
with more detail. Use the unsharp masking carefully as too much of this effect can produce an
undesirable "glow" around objects. Over sharpening is not always
noticeable on the screen, so be sure to test the various sharpening levels with a
proofing system. If your scanning software doesn't have an Unsharp Masking or
Sharpening option, you can do this in the image editing program after the scan.
Color Controls and Contrast: Most
scanning software has controls for adjusting the colors and contrast of the
image while you scan. The color and contrast controls are also in the image editing software. As
a general rule, adjusting the controls as you scan is better than editing the
image later when using image editing software. If you scan with a 30-bit scanner you are
working with more color data than the limits of RGB after the scan and you get
better results. If, however, your scanner is 24-bit, then it doesn't really
matter where you do the editing because the color data is the same.
In order to get good results and predictable color, you must calibrate your
and your monitor
often and use color
Mode or Line Art: Bitmap mode means that the image is in black and white only.
Another way to describe bitmap is as one-bit, since each pixel is either "on" or
"off" (white or
that you would scan as bitmap would be logos, signatures, and line drawings.
This type of artwork is also called line art because the images are made
of clean lines. Line art should be scanned at the highest resolution possible
if outputting on an imagesetter or platesetter to get the best results.
If the end result will be printed on an inkjet or laser printer, scan the
image at the highest resolution your printer will allow.
Threshold: If you scan an image in bitmap mode that has levels of gray
in the image, then the gray colors are converted to either black or white depending
on the density of light or darkness in the color. You can set the level at which point the
gray color goes to either black or white. The level you set is called the threshold. Lowering the
threshold means only the darker grays will convert to black; increasing the
threshold means the lighter grays will also convert to black.
is an 8-bit mode, meaning there are 254 shades of gray, plus black and
white equaling 256 different colors.
than for photos, you should use the grayscale mode to scan any sketches or pencil drawings that
have different shades of gray.
not scan as grayscale if the images have smooth lines and are just one
color, such as signatures. Images that smooth lines and that are
one color should be created in bitmap mode.
Grayscale mode does not create perfectly smooth lines.
- CMYK Conversion: Most scanners scan the image in RGB, although the
high-end scanners can digitize the file directly in CMYK.
It is a
good idea to work on your image while it is still in RGB mode because RGB
files are smaller. They will open and be saved faster than CMYK files. Some
filters and effects are only available in RGB mode.
for the image to be printed on a press, it needs to be converted to CMYK. Before you
convert, first save the RGB file, because once you convert it to CMYK, you cannot
get back the lost pixels from the original file. Converting back and forth
between RGB and CMYK will cause loss of information in the image. Do the RGB to
CMYK conversion once, and make it the last step that you do. To convert in
to the "Image Menu", then to "Mode" and select "CMYK
Color". You might want to talk to
your printer for any specific settings that they want you to use before converting.
Remember that some colors in RGB cannot be reproduced in CMYK
because they are "out of gamut". Programs like Photoshop® let
you know if a selected color will not print in CMYK by showing an alert
symbol on the color palette.
OCR (Optical Character Recognition): When text
is scanned it is recorded as a bitmap image. The scanner does not distinguish
text from an illustration. In order to edit the text, it needs to be translated
into ASCII characters by an OCR system. The OCR system can also check for
accuracy and spelling and then save the text in different formats. The saved
text can either be opened in a word processing program or it can be imported
into a page layout program.
OCR requires at least 200 dpi resolution from the scanner to be able to
function and the text being scanned needs to be clear for the highest accuracy.
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