descreen on or off?

N
Posted By
Nikko
May 24, 2004
Views
492
Replies
9
Status
Closed
I just scanned the same picture twice. Once with Descreen off but the Unsharp Mask on, the second with Descreen on and no Unsharp Mask (won’t let me pick both at the same time- I assume that’s standard?). The file with Descreen on is 1.25 MB, while the one with it off is 2.5 MB. Any reason for the discrepancy? I’m just wondering why the first file is so small. Am I losing information and, as a result, picture quality?

Is there a general consensus on the effectiveness of Descreen? Is there a better way to fix the moir
MM
Marvin Margoshes
May 24, 2004
"Nikko" wrote in message
I just scanned the same picture twice. Once with Descreen off but the Unsharp Mask on, the second with Descreen on and no Unsharp Mask (won’t
let
me pick both at the same time- I assume that’s standard?). The file with Descreen on is 1.25 MB, while the one with it off is 2.5 MB. Any reason
for
the discrepancy? I’m just wondering why the first file is so small. Am I losing information and, as a result, picture quality?

Is there a general consensus on the effectiveness of Descreen? Is there a better way to fix the moir
T
tacitr
May 24, 2004
I just scanned the same picture twice. Once with Descreen off but the Unsharp Mask on, the second with Descreen on and no Unsharp Mask (won’t let
me pick both at the same time- I assume that’s standard?)

Yes, that is standard.

Descreen is used to scan an image that has been screened, which means printed with a pattern of dots. A printing press is not capable of printing any shades of color or gray; shades of color or gray are "faked" using a "halftone screen," which is a pattern of dots spaced close together. (Look at a newspaper with a magnifying glass and you’ll see.)

Anything printed on a printing press–including posters, newspapers, magazines, brochures, and anything like that–should be scanned with "descreen" on. Otherwise, you end up with a pattern of dots rather than a picture. Anything that is truly photographic, like a photographic print or a negative, should be scanned with descreen off.

Unsharp mask makes a picture sharper. if you turn on unsharp masking with a screened image, the pattern of dots is sharper and more exaggerated–exactly the opposite of what descreening does.

The file with
Descreen on is 1.25 MB, while the one with it off is 2.5 MB.

How did you save the file?

The size of the file depends on the resolution and size of the scan. Descreen on or off will not affect this in the slightest. However, if by "size of file" you mean "I saved a JPEG," then there might be a difference in the size of the JPEG, because a JPEG file is compressed, and the amount of compression depends partly on how many hard edges are in the image.

But JPEG compression degrades the quality of the image, and JPEG is only useful where file size on disk is important and image quality is not. So of course you would not save a scan you just made as a JPEG, right? Not unless it absolutely had to be a JPEG and no other format would work–for example, for the Web.

Is there a general consensus on the effectiveness of Descreen?

Most scanner’s descreen function works well. It depends on how good the scanner’s software is.

Is there a
better way to fix the moiré (or whatever it’s called – sorry, I’m a novice) using other software?

If the morie is being caused by the halftone screen, the best way to fix it is with the descreen function–the scanner will remove the moire as the image is being scanned, while it’s still in its most raw state. Descreening after the scanner is done makes for a picture whose quality is not as good, because the scanner has more information to work with.


Biohazard? Radiation hazard? SO last-century.
Nanohazard T-shirts now available! http://www.villaintees.com Art, literature, shareware, polyamory, kink, and more:
http://www.xeromag.com/franklin.html
EG
Eric Gill
May 24, 2004
"Marvin Margoshes" wrote in
news::

"Nikko" wrote in message
I just scanned the same picture twice. Once with Descreen off but the Unsharp Mask on, the second with Descreen on and no Unsharp Mask (won’t
let
me pick both at the same time- I assume that’s standard?). The file with Descreen on is 1.25 MB, while the one with it off is 2.5 MB. Any reason
for
the discrepancy? I’m just wondering why the first file is so small. Am I losing information and, as a result, picture quality?
Is there a general consensus on the effectiveness of Descreen? Is there a better way to fix the moir
RH
Ron Hunter
May 24, 2004
Nikko wrote:

I just scanned the same picture twice. Once with Descreen off but the Unsharp Mask on, the second with Descreen on and no Unsharp Mask (won’t let me pick both at the same time- I assume that’s standard?). The file with Descreen on is 1.25 MB, while the one with it off is 2.5 MB. Any reason for the discrepancy? I’m just wondering why the first file is so small. Am I losing information and, as a result, picture quality?

Is there a general consensus on the effectiveness of Descreen? Is there a better way to fix the moiré (or whatever it’s called – sorry, I’m a novice) using other software? I have both Photoshop 6.0 and Elements 2.0, should either of those help. Or is it better to make the adjustment with the scanner itself?

Any advice you can pass along to this newbie would be much appreciated. Thanks!
Yes, you are losing the objectionable moire patterns, and the extra file size they generate. Descreening does add some processing time to the scan, but fixing this problem at the scanner seems the best approach in my experience.
N
Nikko
May 24, 2004
"Eric Gill" wrote in message
"Marvin Margoshes" wrote in
news::

Disregard that completely – exactly the opposite is true. It’s better to descreen at scan time.

A possible reason for the size difference is some scanners limit the resolution they will use in Descreen mode. A second option is that you are saving in JPEG; descreening can defocus an image, which compresses better, sometimes remarkably so.

I guess I’m confused. The image I descreened does indeed look less sharp (i.e. less focused). Isn’t this bad? Am I missing something?
EG
Eric Gill
May 24, 2004
"Nikko" wrote in news:YMtsc.7988$Tn6.2447
@newsread1.news.pas.earthlink.net:

"Eric Gill" wrote in message
"Marvin Margoshes" wrote in
news::

Disregard that completely – exactly the opposite is true. It’s better to descreen at scan time.

A possible reason for the size difference is some scanners limit the resolution they will use in Descreen mode. A second option is that you are saving in JPEG; descreening can defocus an image, which compresses better, sometimes remarkably so.

I guess I’m confused. The image I descreened does indeed look less sharp (i.e. less focused). Isn’t this bad?

Depends.

It’s a tradeoff. Less sharp for no nasty pattern.

Your call on how much sharpness you want to give up, i.e., is the picture going to look worse soft or screened?

Am I missing something?

Nope. This is more an art than a science. Some scanners are better than others, some screen patterns are worse or non-standard and therefore aren’t handled well by automatic descreening.
N
Nikko
May 24, 2004
"Tacit" wrote in message

The size of the file depends on the resolution and size of the scan.
Descreen
on or off will not affect this in the slightest. However, if by "size of
file"
you mean "I saved a JPEG," then there might be a difference in the size of
the
JPEG, because a JPEG file is compressed, and the amount of compression
depends
partly on how many hard edges are in the image.

But JPEG compression degrades the quality of the image, and JPEG is only
useful
where file size on disk is important and image quality is not. So of
course you
would not save a scan you just made as a JPEG, right>

Ok, what file format would you suggest? TIFF?

Is there a
better way to fix the moir
T
tacitr
May 25, 2004
Ok, what file format would you suggest? TIFF?

TIFF and Photoshop (.psd) are both good formats for saving work, yes.

I don’t know exactly how the original images were made (i.e. halftone or not). They are black and white photographic prints made in around 1974. Does that in itself reveal anything about how the prints might have been made?

Look at the picture with a magnifying glass. Is it made up of a bunch of tiny, evenly-spaced dots? If so, use the descreening.

At any rate, the moiré I saw wasn’t nearly as bad as something that’s scanned from a magazine or newspaper. So would you suggest still using the
descreen or is it better treated with software after the fact? Or does that
not change your answer at all?

Depends. If the moire is coming from a halftone screen, then use the descreening filter; if the moire is a "content moire" (that is, an artifact of what the picture is OF–for example, a picture of a fine mesh or screen will often show a moire), then you may not be able to use the scanner’s descreening function, and may have to remove the moire in another program. —
Biohazard? Radiation hazard? SO last-century.
Nanohazard T-shirts now available! http://www.villaintees.com Art, literature, shareware, polyamory, kink, and more:
http://www.xeromag.com/franklin.html
RH
Ron Hunter
May 25, 2004
Nikko wrote:

"Eric Gill" wrote in message

"Marvin Margoshes" wrote in
news::

Disregard that completely – exactly the opposite is true. It’s better to descreen at scan time.

A possible reason for the size difference is some scanners limit the resolution they will use in Descreen mode. A second option is that you are saving in JPEG; descreening can defocus an image, which compresses better, sometimes remarkably so.

I guess I’m confused. The image I descreened does indeed look less sharp (i.e. less focused). Isn’t this bad? Am I missing something?
Yes, it IS less focused, but then that is MUCH better than the moire patterns. Try testing to see for yourself. You can sharpen after the scan.

Related Discussion Topics

Nice and short text about related topics in discussion sections