Message-Id: <200103240539.WAA09216@dns.ccit.arizona.edu> Date: Fri, 23 Mar 2001 22:37:24 -0700 From: Tim Au Yeung <mailto:ytau@UCALGARY.CA> Subject: Re: Photoshop question To: mailto:IMAGELIB@LISTSERV.ARIZONA.EDU
<pre>
Hello Judith,
I'm not a true "expert Photoshop user" but I have had a bit of experience
with scanning.
> The question we have has to do with determining which working space
> setting we should use for our gray scale scans in Photoshop 6.0. The
> default gray scale setting is selected from the Color Settings Dialog
> box. Should the Gray working space be Gamma 2.2 or Dot Gain 20% or
> some other setting? We found that we when we used the "Dot Gain 20%"
> setting the image on the screen more closely resembled the source
> photograph than the Gamma 2.2 setting. We calibrated our monitor using
> Adobe Gamma, but of course, this is a pretty subjective evaluation
> (reliant on the ambient lighting, users perceptionetc.).
When you talk about Gamma and Dot Gain, you're talking about two different
concepts. Dot gain refers to an offset printing situation and describes how
much a dot of ink will spread on a given type of paper. Gamma on the other
hand, refers to the general tonal curve of the color space you're working
in. The Mac environment has a gamma of 1.8 while a Windows environment uses
sRGB which has a gamma of 2.2. Notice that I'm refering to an RGB
environment when talking about gamma. The majority of calibration issues
revolve around colour and bias in the colour channels. Greyscale is usually
much easier to deal with.
> From the reading I have done, you should choose as the default setting
> that which "most closely matches the behavior of your most common
> grayscale output." (Bouton, Gary. Inside Adobe Photoshop 6).
> However, as described, we have not scanned the image with a specific
> device in mind, (although, we DO plan to purchase an Epson inkjet
> printer so that we can make in house copies of photographs). The
> default working space profile we select in the Color Settings dialog
> box applies to newly created files.
>
> Judith
>
> Judith A.K. Terpstra
> Information Access
> 6921 Brayton Drive #210
> Anchorage, AK 99507
> Phone: (907) 349-7478
> Fax: (907) 344-7958
One important consideration is the fact that you are talking about profiles.
The idea behind profiling is to characterize the device that you're working
with and the device that you output to. Therefore, all scanners, monitors,
and printers can be profiled which, of course, works best in a closed loop
environment. In your case and in most archival cases, I wouldn't worry too
much about a target profile as you won't know what kind of device that the
image will be output to eventually. The most you really want to do is to
correct for the bias inherent in the scanner.
The easiest way to do this is to use an IT8 target in every scan you do,
particularly given the care you are putting in to the size and bit depth of
the image. If you're not familiar with an IT8 target, it looks like a
photograph with an image and a series of color blocks and a graded series of
greys on the side. There are targets specific for greyscale but sometimes an
IT8 target is easier to get ahold of, especially since no one develops black
and white photography in a lab environment anymore. If you scan this with
every image, you'll have a fixed scale to balance against, allowing you to
correct tone against a fixed set of values (which should be black from 0% to
100% in 10% increments) that you can do by the numbers rather than visually.
It also leaves a record of adjustments that you might have made to improve
the look of the image.
In addition, there are the usual recommendations for producing better scans
including limiting ambient light as much as possible, using 5000K lighting,
turning on your monitor and leaving it on an hour before doing work,
balancing your monitor on a regular basis. Also, if you do use an IT8 target
or similar, budget in to replace it on a regular basis as they do fade over
time. As a final consideration, you may want to get the correct ICC profiles
for your monitor (which may be available from the manufacturer), adjust for
your specific monitor and embed the profile. Same for the scanner. This is
another trace that allows someone later on to identify the general bias in
the image and retarget for their specific conditions.
Tim
--------------------------------
Tim Au Yeung
Manager, Digitization Initiatives
Alberta Heritage Digitization Project
Information Resources (Press)
University of Calgary
voice: (403) 220-8975
e-mail: ytau (at) ucalgary.ca
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