Computer Graphics with Photoshop - descreen on or off?

Author

descreen on or off?

Nikko

2004-05-24, 7:14 pm

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!

Marvin Margoshes

2004-05-24, 7:14 pm

"Nikko" <nothanks@yourmomma.com> wrote in message
news:Sjqsc.7377$Tn6.3862@newsread1.news.pas.earthlink.net...
> 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!
>
>

Descreen is for use in scanning half-tone photos, for example from a
newspaper. If you are seeing a Moire pattern, try using the Moire removal
function in an editing program, like Paint Shop Pro. You are much better
off with doing such functions in editing software, than while making the
scan.

Tacit

2004-05-24, 7:14 pm

>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

Eric Gill

2004-05-24, 7:14 pm

"Marvin Margoshes" <physnospamchem@cloud9.net> wrote in
news:10b4ek4njsp2r4c@corp.supernews.com:

>
> "Nikko" <nothanks@yourmomma.com> wrote in message
> news:Sjqsc.7377$Tn6.3862@newsread1.news.pas.earthlink.net...
> let
> for
> novice)
>
> Descreen is for use in scanning half-tone photos, for example from a
> newspaper. If you are seeing a Moire pattern, try using the Moire
> removal function in an editing program, like Paint Shop Pro. You are
> much better off with doing such functions in editing software, than
> while making the scan.

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.

Ron Hunter

2004-05-24, 7:14 pm

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.

Nikko

2004-05-24, 7:14 pm

"Eric Gill" <ericvgill@yahoo.com> wrote in message
news:Xns94F3894F1FFDDericvgillyahoocom@24.93.43.119...
> "Marvin Margoshes" <physnospamchem@cloud9.net> wrote in
> news:10b4ek4njsp2r4c@corp.supernews.com:
>

> 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?

Eric Gill

2004-05-24, 7:14 pm

"Nikko" <nothanks@yourmomma.com> wrote in news:YMtsc.7988$Tn6.2447
@newsread1.news.pas.earthlink.net:

>
> "Eric Gill" <ericvgill@yahoo.com> wrote in message
> news:Xns94F3894F1FFDDericvgillyahoocom@24.93.43.119...
>
>
>
>
> 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.

Nikko

2004-05-24, 11:14 pm

"Tacit" <tacitr@aol.com> 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?

>
novice)[color=darkred]
>
> 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.

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? 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?

Thanks again for all you help.

Tacit

2004-05-24, 11:14 pm

>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

Ron Hunter

2004-05-25, 4:14 am

Nikko wrote:

> "Eric Gill" <ericvgill@yahoo.com> wrote in message
> news:Xns94F3894F1FFDDericvgillyahoocom@24.93.43.119...
>
>
>
>
>
>
>
> 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.