Re: color profile embedding (not conversion) utility?

On 3 Nov 2005 14:36:13 -0800, "blumesan" <blumesan@xxxxxxxxxxx> wrote:

>There is a bit of confusion (at least on my part) about the meaning of
>a "tagged image". Putting this aside for the moment, the meaning of
>"embedded profile" is quite clear. To me, an embedded profile
>describes the color space of its associated file. The file was either
>created in that color space or subsequently converted (from whatever
>color space it was in, e.g. raw scanner) into that color space. Thus
>when I find that the file output by the scanner software has an
>embedded profile (sRGB) it suggests that the "native" scanner data have
>been converted into this color space before writing the file to disk.
>That, of course, requires changing the data. [See my previous post to
>John which describes my workflow and PS color settings.]

I think I better "tag" John, now... ;o)

You see, I only have Photoshop version 6 here so John's remarks are
much more appropriate. PS 6, for example, totally ignores EXIF data
and strips it all away when the file is saved (a major annoyance for
my digicam images!).

Having said that, I think a part of the problem is probably the
terminology as well, so let's settle for Photoshop terms.

Assign (or Tag as we have been calling it) simply means a marker is
saved with the file indicating the profile to be used but the image
data is not changed.

Assign and Convert, by contrast, means change the image data.

Finally, "Leave as is..." as Photoshop calls it means don't do
anything to the file; don't assign a profile and don't change the
data.

BTW, you can test all this out as follows. Take a scan without a
profile and import into Photoshop. Assuming your preferences are set
to "Ask" a dialog pops-up. Select "Leave as is..." and then save the
image as RAW. When you do that only image data is saved without any
prefix or suffix (which is where profiles, tags, EXIFs, etc live).

Close and open the same image again. This time select "Assign
working..." and again "Save as" using the RAW option.

Finally, close again and open but select the third option "Assign"
click the check mark for "convert". Again, save as RAW.

You can then compare these three files to see what action causes image
data to change. If you don't have a compare program, you can use "fc"
(file compare) in DOS. Type "fc /?" for parameters.

>> "Of course, a re-scan will take longer, so you'll have to decide if
>> that extra accuracy is really worth the trouble of waiting for another
>> preview scan."
>
>Your phrase "waiting for another PREVIEW scan" adds to my confusion.
>As noted above, when I select "Redraw" the scanner performs another
>preview scan.

It could have been the NikonScan version (I used both 3 and 4 over two
scanners LS-30 and LS-50) but I remember distinctly that in some cases
the image was just redrawn instantly without performing the new scan.

Anyway, I don't use NikonScan anymore, but if every time you press
Redraw the scanner does perform another preview scan then everything's
fine and just ignore what I said.

BTW, you probably know this, but an exclamation mark in a yellow
triangle indicates when the Analog Gain settings has been changed but
the display was not updated with a Redraw. This icon appears in the
information panel.

>> "Do note that what you see there is based on the preview image! Nikon
>> Scan is good in that it actually uses the full 16-bits for the preview
>> but the resolution is greatly reduced and the histogram display is
>> only 8-bit. That means once you import the full scan into Photoshop,
>> there may be some small differences. Do note also that Photoshop
>> histogram is 8-bit too. If you want more accuracy here's a free 12-bit
>> histogram you can use as a Photohop plug-in:"
>
>It is my understanding that when the image imported into PS was 16 bit,
>the histogram display used all 16 bits. I am using PS CS(8). Please
>correct me if I am wrong.

There are two issues here. One is that Photoshop's 16-bit mode is
actually 15-bit. At least for version 6. I'm not sure about version 8
but I believe that hasn't changed. Maybe someone else can jump in to
clarify this. If so then any histogram uses this reduced 15-bit image.

The second issue is more important, because the Photoshop histogram
display (at least in version 6, again) is only 8-bit i.e the data is
reduced to fit into 256 bins available in the display window.

Don.
.

Relevant Pages

  • Re: Don, need your help with Nikon Scanner
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  • Re: color profile embedding (not conversion) utility?
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    (comp.periphs.scanners)
  • Re: Color management work flow questions...
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