Re: color space of a scanned image

Hi Wil,

Internally, our scanner works in the so called "device color" space.
This is a rather random color space, depending on the design and
production tolerance of your scanner.

To produce the expected results, the scanner driver automatically
converts the images to the Windows color space "SRGB". This conversion
is where you (may) loose quality.

The conversion is done with a "canned" profile, that matches your
scanner model but doesn't account for the production tolerances.
Scanning the same original with two scanners (same model) may give
slightly different results. Also, recent scanner drivers optimize for
family photos. The images may undergo several "enhancements", that
produce more pleasant (but less exact) results.

If you are happy with the quality as it is, you should assume SRGB and
convert to LAB.


If you're not happy, you should eliminate the driver conversion from
the workflow. You should scan directly in "device color" mode, and
then assign your scanners ICC profile (not altering the image data).

Scanning in "device color" mode might be possible with your driver.
Check all dialogs and turn off all enhancements. If this doesn't help,
try VueScan (http://www.hamrick.com). This software talks to your
scanner directly, circumventing the driver. For your purposes
deactivate all color-management options and set the output color space
to "DEVICE RGB".

Assigning the ICC profile can be done with Photoshop. First you need a
profile. You can try the canned one, many drivers install it as
regular ICC profile or contain it in their installation ZIP file (as
..ICM file).

Make sure that you "assign" the profile, do not "apply" it. That is,
the image data doesn't change but rather is only interpreted in a
different way. This preserves all captured information from the
original.

If you're not happy with the canned ICC profile (or can't find it), you
can create a specific profile for your scanner unit. This gives very
good results. To do it, you need a color target (like the R1 item on
http://www.targets.coloraid.de) and a software like Gretag MacBeth
ProfileMaker Pro 5 (or send the scanned image of the target to a friend
who has access to this software).

Marc

.

Relevant Pages

  • Re: correct colors
    ... I can understand that an ICC profile is necessary to convert ... shouldn't the scanner software contain its own ICC profile to correct ... do and the scans are quite consistent from scan to scan. ... spectral characteristics of the paper used can alter the scanner response. ...
    (comp.periphs.scanners)
  • Re: color space of a scanned image
    ... When you said RGB, do you mean sRGB? ... When a scanner is set up, the ICC profile is installed automatically and is ... know what color space the image files are now in. ...
    (sci.image.processing)
  • Re: color space of a scanned image
    ... Actually I think the color measurement is not very important in my ... With a color profile you are probably getting sRGB from the scanner. ... If you used an ICC profile, you probably got sRGB, so converting to ...
    (sci.image.processing)
  • Re: correct colors
    ... The scanner doesn't accurately scan ... I can understand that an ICC profile is necessary to convert ... spectral characteristics of the paper used can alter the scanner response. ... spectra and the filters in the scanner all contribute to inaccurate ...
    (comp.periphs.scanners)
  • Re: Profiles and gamuts
    ... > I'm still knew at all this but am I correct in saying that "scanner ... > profile" is basically my capture device's (Nikon V) output? ... When I compare that to sRGB (with sRGB as ... colors in the monitors color space. ...
    (comp.graphics.apps.photoshop)
Quantcast