|
When I scan an image, why
is the result very low resolution?
Why do my images come out blurred? Why do scans come out "blocky"? The
scanner keeps enlarging my images. The edge of my scans keep being missed.
UMAX's "AutoScan" utilities will only capture an image a a very low resolution
(typically 100dpi), intended to give a quick scan for screen purposes - for high quality
printouts and detailed images on-screen, it is best to use the Manual Scan driver to
change the resolution to a more suitable setting. To change the scanner driver to Manual,
use the "Select Source" option in your imaging program.
If scans always appear too large on screen or "blocky" check to see if the
imaging program is magnifying the image to fit on the screen - although the scanned image
isn't affected, most programs display the scan at the size that best fit the screen or
window, making the scan look larger or smaller than it really is. You can normally change
the screen view using a Magnifier tool (or look for options in a View or Windows menu) -
this won't affect the size that an image is printed out at.
If printed images always seem to be missing an area around the edge of the original image,
this is due to the printer only having a limited print area (most printers can only print
to within 5mm of the edge of a page). To make all of an A4 picture fit on a printed A4
page, remember to either scan at a slightly reduced scaling - eg 95% - or change the
printer driver settings to "scale to fit page".
What resolution do I need to scan at for my desktop printer?
Why do my scans take so long? Printing my scanned images takes hours. When I scan at
the resolution of my printer (eg 1440dpi) images are soft and blurred when I zoom in to
look closely.
Here are the most common scanning resolutions that are used:
| Resolution (dpi) |
Usage |
| 72 |
Scanning images for use on the
screen only or for use in web pages |
| 150 |
For medium quality print-outs
using ANY resolution of inkjet or laser printer. |
| 300 |
For high-quality print outs using
ANY resolution of inkjet or laser printer. The same resolution is used for most
professional magazine printing! |
| 600 |
For scanning line drawings or
enlarging small originals only. |
| 601+ |
Images above 600dpi (for a
scanner with a 600dpi resolution) are processed to add in extra dots of colour, but don't
show any more of the detail in the original image - the best use for 601+dpi is lineart
images or fine drawings. |
| 4800 |
Probably the highest setting available in the
software, most of the image is "invented" by the computer using the 600dpi
"optical" (maximum) resolution of the scanner hardware - extremely rare
commercial use. |
Although scanner software offers very high
("interpolated") resolutions, it is rare that these are useful - even in
professional graphics, 300dpi is the normal resolution for high quality work. The
advantage of higher resolution scanners is being able to enlarge small originals. Although
some desktop printers now offer resolutions of 1440dpi, most of this resolution is used to
produce the very fine rosette (screening, dithering) pattern needed to print a range of
colours - it is very difficult to see any difference between a printed 300dpi and 1440dpi
scan!
Although most desktop colour printers use 4 colours of ink to print images - Cyan,
Magenta, Yellow and Black (CMYK) it is often possible to get better results, more quickly
using the "RGB" (red, green, blue) colour format. RGB images are displayed much
more accurately on a computer screen and printer's own software often performs the best
conversion to CMYK for colour output.
When scanning at full resolution I keep getting "out of memory errors"
How much disk space will a scan use? How much memory and fre disk space
should I have?
Scanning at high resolutions can produce very large files - a 72 dpi colour (RGB) scan of
an A4 page uses 1.43MB of disk space; 300dpi uses 24.9MB; 600dpi uses 99.6MB; 4800dpi
requires around 6.4 Gigabytes! As a general rule a PC should have at least as much RAM as
the image to be scanned and at least double the free disk space on the system hard disk
drive - more than this will improve the scanner's and computer's performance. Note: CMYK
scans are 25% larger than RGB scans; greyscale scans are one third of the size of RGB
scans.
When I enlarge a photograph the result is very blurred - my scans always seem
"soft" or out of focus.
Using an Astra scanner and a transparency adaptor, scans of 35mm film comes out
blurred. How much can I enlarge a photograph? Do I need a transparency adaptor to scan
films or negatives?
When you scan an photograph or transparency, in the most cases you will be trying to
produce an image of the same size (dimensions), ie 100% scaling (or an enlargement of 1x).
With a scanner of 600dpi resolution, it is possible to enlarge an image by different
amounts depending on the resolution required (see table above). An image caould be scanned
at 600dpi, 100% or 300dpi, 200% or 150dpi, 400% or 72dpi, 833%. Although you can choose
higher resolutions and scalings in the scanner software when you exceed the scanner's
"optical resolution" (600dpi for Astra 610S/610P/1210P, 1200dpi for Astra 1200,
1220, 2000 and 2100 series) the result will be soft and out of focus - the computer has to
invent the extra dots of colour required in addition to those the scanner can capture. The
only way to increase the optical resolution of a scanner is to buy a higher specification
model - a 2000dpi scanner may cost thirty times as much as a 600dpi model!
The limiting optical resolution of the scanner also determines how useful it is for small
originals - owners of a 600dpi scanner will only be able to enlarge photographs or films
by two to four times, which is of limited use for 35mm film and slides. Another big
difference between 600dpi scanners and the "professional" 2000dpi models is the
amount of detail that can be captured in dark areas of film - more noise will be visible
when using an Astra 600 scanner than a much more expensive model. We describe the
Transparency Adaptor for the Astra scanners as being suitable for "positional
scans" - images to be used only on the screen at low resolution.
Transparency adaptors are required for scanning any originals that would normally be
backlit - slides, film strips, negatives, "trannies"etc: inside the adaptor is a
specially calibrated lamp which is moved down the length of the scanner using a very
accurate motor. It is not possible to scan slides or film by projecting their image on to
the glass of the scanner.
The colours in my scan aren't the same as those in my original photograph - how
can I improve the colour matching?
All of my scans appear too dark or too light. My scans all have a colour cast. Images
on my screen don't look like my printouts.
Colour matching is a complicated issue as it involves the scanner's controls, the monitor,
the printer driver, the printer, settings in the image application and many other
controls. You can read more about these in a separate technical
note, however here are some simple tips for correcting colour problems if you don't
have much experience of digital imaging:
1. The screen is a more accurate device than a printer - if the results on the scrren look
bad, increase the number of colours being displayed to the maximum possible (in your video
card settings or display preferences); a minimum of 32,000 colours are required to display
colour photographs properly (ideally 16.7 million!).
2. If images consistently appear too dark or light on the screen or print out, try chanign
the controls in the scanner driver: Copy Utility includes a brightness control, the manual
scanner driver has several controls as well as an Auto Adjust option. Try turning on the
"MagicMatch" option with the mode set to RGB - if your imaging program supports
CMYK scans you can lso try MagicMatch with your printer's profile selected (or an
equivalent model).
3. If printouts consistently have a colour cast, such as a red bias, then adjust the
overall Red in the image either a. by using the scanner driver controls or b. by looking
for printer calibration settings in your printer driver (the second option is far better).
4. If you consistently get good images on screen but poor printouts which don't match the
screen or the original, check your printer settings, the printer manual or call the
printer manufacturer for further advice - the printer may have a fault or its settings may
need adjusting.
. |
