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Re: "Assigning" vs. "Matching" a color profile

 
 
me
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      12-29-2009
On Mon, 28 Dec 2009 11:11:08 -0800, isw <(E-Mail Removed)> wrote:

>This is on a Mac, BTW.
>
>I have a large number of scanned slides bearing a color profile
>(assigned by the scanner) that gives iPhoto fits; I'd like to change it.
>
>Using ColorSync, I can "assign" a different profile, or I can "match" to
>a different profile, but I do not understand which I should do, or (more
>importantly) what the difference is between the two. Further, I don't
>know which profile I should move to: "Generic RGB"; "sRGB"; or what? The
>images are my own, and will not be displayed on the web. I'd like to
>keep them at the highest possible "accuracy" (whatever that means).
>
>A whole lot of googling has produced many descriptions of *how* to do
>these things, but nothing on *why* or *which*.
>
>Can anybody shed some light, please?



I've seen the other give and take on this and believe a fundamental
concept is missing here. The profile assigned to the image by the
scanner contains the information of how the colors mapped by the
scanner correspond to the reference color space. A color space aware
app is needed to read this. This then gets translated into the working
color space of the app. Finally a monitor or printer profile is used
to again translate this into the monitor or printer color space.

Simply assigning a different color profile is not the answer. You need
to convert to a different profile and then resave that image with the
new profile. Not knowing anything about iPhoto I don't know if "match"
to a different profile is what you want here, but suspect it might be.
Check the help file for this function. Note that by doing this you
will actually changing the color data in the image (IIRC)
 
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me
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      12-29-2009
On Tue, 29 Dec 2009 09:45:48 -0800, isw <(E-Mail Removed)> wrote:


>I'm OP, and I agree with what you've said, now that I finally understand
>it. Now, the remaining question is, what is the preferred profile to
>change to?
>
>Considering that there will certainly be improvements in the gamut
>capabilities of display devices in the future, I'm thinking that sRGB is
>probably too constraining. How about ProPhoto?



First, what matters is the content of your images, not necessarily
what colorspace they are in. Even though the scanners color space may
be larger than sRGB or AdobeRGB, what matters is the actual colors
contained. Can iPhoto show out of gamut colors? You could then see
what colors are contained/maintained in a given color space. You also
haven't mentioned what format you are saving in. A wider color space
may bring about issues given the wider space must fit into a given
amount of storage bits and hence there may be less graduations of a
given color available.
 
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MikeWhy
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      12-30-2009
"isw" <(E-Mail Removed)> wrote in message
news:isw-4A37D4.20315329122009@[216.168.3.50]...
> In article <(E-Mail Removed)>,
> me <(E-Mail Removed)> wrote:
>> You also
>> haven't mentioned what format you are saving in. A wider color space
>> may bring about issues given the wider space must fit into a given
>> amount of storage bits and hence there may be less graduations of a
>> given color available.

>
> Saving as "high quality" JPEGs; these are 35mm slides, scanned at 4800
> ppi on a scanner that *claimed* to be able to handle it. But there's
> nothing about the JPEG encoding process that forces a restricted gamut.
> Storage space is not an issue, but I need to deal with iPhoto's problem
> with the scanner's profile, and I don't want to throw anything away in
> the process.


Then you should archive the scans as they are, without converting the
colorspace. Your choices for JPEG are 8 bit and 16 bit. As he pointed out,
converting to a larger gamut requires more bits to maintain the same
gradation in the larger space as 8 bits in the smaller color space. A
lossless conversion will double the size of each file in the new colorspace.

Would you mind posting or emailing a small crop of a 4800 ppi scan? I have
never seen a scan that fine. Can your scanning service handle medium format
and sheet film sizes? What technology do they use?


 
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me
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      12-30-2009
On Tue, 29 Dec 2009 20:31:53 -0800, isw <(E-Mail Removed)> wrote:


>I don't think so. But that's not the issue. I don't care whether iPhoto
>(or any other specific image handling app) can display the full gamut of
>the images; what I want is to not lose something that might be usable on
>*future* imaging equipment, whether a better screen, or a printer, or
>whatever.


Unless you have verified there are actual colors in the scan outside
of sRGB or aRGB this obseeion with colorspace is just that, an
obsession with little real implication. Given this course of reasoning
IMO you would have been much better off saving the orignal scans to 24
bit tiffs for the archival originals. Except if you have some raelyy
special images I would doubt the color info lost would come anywhere
close to the tonal graduation info lost saving to jjpeg.
 
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MikeWhy
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      12-30-2009
isw wrote:
> In article <hhfv18$s6c$(E-Mail Removed)-september.org>,
> "MikeWhy" <(E-Mail Removed)> wrote:
>
>> "isw" <(E-Mail Removed)> wrote in message
>> news:isw-4A37D4.20315329122009@[216.168.3.50]...
>>> In article <(E-Mail Removed)>,
>>> me <(E-Mail Removed)> wrote:
>>>> You also
>>>> haven't mentioned what format you are saving in. A wider color
>>>> space may bring about issues given the wider space must fit into a
>>>> given amount of storage bits and hence there may be less
>>>> graduations of a given color available.
>>>
>>> Saving as "high quality" JPEGs; these are 35mm slides, scanned at
>>> 4800 ppi on a scanner that *claimed* to be able to handle it. But
>>> there's nothing about the JPEG encoding process that forces a
>>> restricted gamut. Storage space is not an issue, but I need to deal
>>> with iPhoto's problem with the scanner's profile, and I don't want
>>> to throw anything away in the process.

>>
>> Then you should archive the scans as they are, without converting the
>> colorspace. Your choices for JPEG are 8 bit and 16 bit. As he
>> pointed out, converting to a larger gamut requires more bits to
>> maintain the same gradation in the larger space as 8 bits in the
>> smaller color space. A lossless conversion will double the size of
>> each file in the new colorspace.
>>
>> Would you mind posting or emailing a small crop of a 4800 ppi scan?
>> I have never seen a scan that fine. Can your scanning service handle
>> medium format and sheet film sizes? What technology do they use?

>
> The scanner is a consumer-grade unit from Microtek; I acquired it a
> few years ago for under $200. I'm under no illusions about how good
> the scanner is with regard to dark noise and so on, but I wanted at
> least to start out with high spatial resolution. I have several
> thousand slides, and simply couldn't afford to have them
> "professionally" scanned.
>
> I've posted four screenshots from GIMP here:
>
> http://profile.imageshack.us/user/isw/
>
> The images are in reverse order, but I couldn't figure out how to
> rearrange them; I rarely post images.
>
> The ruler at the top of the screenshots (in mm) and the info at the
> bottom give some scale to the images, and to the scanner's pixel size.
> The actual pixels don't begin to show up until about 400%, where 1mm
> is almost the full width of the image. A bit of fringing can also be
> seen at high magnifications, but I really don't know whether it is
> due to the scanner, or is in the original photo (which I can't access
> right now).


Thanks. That was pretty interesting. Yeah, I was curious about the fringing
also. They're likely part of the grain structure, rather than sharpening
halos from the scanner software. Those chemists in Rochester did some really
things, back in the day.

It might be instructive to look at a few slides under a microscope and
compare them with what you see from the scanner. I went through the same
exercise some years ago using an Epson flatbed. 1600 dpi was a bit of a
stretch; I settled for 2400 dpi as a workable compromise. The biggest
problems are flatness and focus. Not owning a drum scanner, I tried glass
mounts and oil briefly. Unmounting, scanning, and remounting each slide
proved even more tedious than it sounds. The lower resolution actually is
quite reasonable and usable. I have no regrets about doing it the way I did.

About the colorspace... I profiled the Epson with MonacoEZColor, and
archived the scans unmodified. I have some doubts about the precision this
chain can achieve, but it's more than adequate for my needs. I batch
converted a "working set" to sRGB, and haven't bothered to dig through the
original scans even once in all the time since.

> The shot was made with a Nikon FTn using a 50mm Nikon
> lens and a circular polarizing filter. In real life, that dish is 64
> meters across; it's the "deep space" antenna at NASA's Goldstone site
> in southern California.
>
> The whole file is about 1.3 MB, and I'll be happy to send it to you if
> you like; just give me an address that won't mind an attachment of
> that filesize.
>
> Isaac


Good luck on your project.

 
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me
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      12-31-2009
On Wed, 30 Dec 2009 20:47:28 -0800, isw <(E-Mail Removed)> wrote:


>Do you have any doubt that Kodachrome or Ektachrome slides can have a
>greater color gamut than sRGB can reproduce? Adobe 98, I'm not so sure,
>but it's certainly wider than sRGB.


You just don't get it do you. Just because the medium, digital or
analog, MAY contain a colorspace of a given size is one thing. Whether
or not it is used is another. That is why I suggested looking at your
scanned images with a color aware application which can be set to
differing working color spaces and then show out of gamut colors.
 
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me
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      12-31-2009
On Thu, 31 Dec 2009 09:35:12 -0800, isw <(E-Mail Removed)> wrote:


>1) Images on Kodachrome originals *may* (depending on the subject
>matter) have a wider gamut than sRGB can handle, and
>
>2) I have no intention of measuring, one-by-one, nearly three thousand
>slides, to find out which ones in fact hold images needing that wider
>gamut and which do not, so


And no one said to do so. Use a little common sense. Pick a few of the
more colorful shots and check them against aRGB. Is anything even
close to being out of gamut? If not then just go with aRGB.


>And right now I'm trying to learn enough to understand the best way to
>do that. So far, my understanding is that sRGB *may* cause a
>(content-dependent) loss of gamut vis-a-vis Kodachrome, and that
>ProPhoto can handle it easily, but is probably too large a gamut unless
>I'm willing to commit to doing everything to 16 bit precision (which I'm
>not). So Adobe98 is my current "best guess" as to what I should convert
>these images to.


So then just do a couple. Compare them against the originals. Even try
subtracting one image from another to see the diff. How big is it?

>Now I need to figure out the least labor-intensive way to do that, and
>why two methods, both provided by Apple, produce visibly different
>results.


Can't help here, since I'm a PCperson. But given decent SW this isn't
that big a deal, with scripting, batch processing, etc.
 
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MikeWhy
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      01-01-2010
"isw" <(E-Mail Removed)> wrote in message
news:isw-5BBB07.09351231122009@[216.168.3.50]...
> 1) Images on Kodachrome originals *may* (depending on the subject
> matter) have a wider gamut than sRGB can handle, and


You still need to consider the scanner's gamut. The hardware itself might
not be up to recording the 'Chrome's full glory; cramming it through the
scanner's profile will already have lost some of the raw information; and
each subsequent remapping will lose still more. If you really want to worry
yourself sick, the 'Chrome itself is an imperfect image of the original
scene.

I read elsewhere you were using the manufacturer's supplied profile, and I
wonder if I should even bring this up. It's better than nothing, of course,
and by itself is probably sufficient to minimize unintended color casts.
MonacoEZColor came with my Epson. It uses IT8 calibration targets, one for
transparencies and another for reflective, to build device specific
profiles. The differences between the stock profile and the custom profile
were rather significant. Switching from one to the other, there were
distinct color pops across the entire image, but none I would consider large
or damaging.

For that matter, I use X-Rite ColorChecker to profile my camera sensors.
There's nothing really wrong with the images as they come out of the camera,
but I find image fidelity improves with the custom profile. Just this
afternoon, because it's still fresh on my mind, I grabbed a quick shot of
soft sunlight caressing a bottle of Hoppe's oil sitting on the window sill.
Before applying the camera profile, the bottle was rendered almost a dull
red rather than Hoppe orange. You could almost feel the texture of the
plastic in your hands looking at it onscreen. (Printing is a whole another
exercise in anality. It's also better to not ask about the monitors and
their calibration.)

Again, there's nothing at all wrong with the images that come of the camera,
even without profiling the sensor. It's the exact same situation as your
stock scanner profile compared to a custom, measured profile. You wouldn't
normally even think about it to complain, but once you start down this road,
everything becomes a mess of profiling and obsessive white balancing and
pixel peeping. You should know upfront where this is taking you.


 
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Wolfgang Weisselberg
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      01-02-2010
isw <(E-Mail Removed)> wrote:

> What I "get" is:


> 1) Images on Kodachrome originals *may* (depending on the subject
> matter) have a wider gamut than sRGB can handle, and


> 2) I have no intention of measuring, one-by-one, nearly three thousand
> slides, to find out which ones in fact hold images needing that wider
> gamut and which do not, so


> 3) What makes sense to me is to handle all the images alike, and in such
> a way that minimal information is lost *no matter the content*.


First: calibrate your scanner. You'll need an IT8 Kodachrome
Target (google!) for your scanner. Otherwise, you're loosing
information right away at the scanner.

Then, save the raw data from the scanner with the ICC profile from
your scanner calibration. That way, you can decide in 10 years
you want to do something different --- and you can start again
right at the point the data came into your computer. That way,
you loose no information past the scanning process.

If you want to have 'final' images (alongside the above named
RAWs!), it depends on what you want to do with them: "display
on the web" or "consumer photo developing", sRGB and JPEG is the
way to go.

> So far, my understanding is that sRGB *may* cause a
> (content-dependent) loss of gamut vis-a-vis Kodachrome, and that
> ProPhoto can handle it easily, but is probably too large a gamut unless
> I'm willing to commit to doing everything to 16 bit precision (which I'm
> not).


Why not?? After all, your primary task is 'loose minimal
information', not 'stay in 8 bit and save disk space', isn't it?

> So Adobe98 is my current "best guess" as to what I should convert
> these images to.


Not really. The best guess is writing a small program that sees if
you loose information *for this given image* at a list of colour
spaces (sorted by size) and choose the colour space and bit depth
that looses none --- then run that over all your images and let
your computer do the work. Don't forget to attach the correct
colourspace to your images.

> Now I need to figure out the least labor-intensive way to do that,


have a program do the work, see above.

> and
> why two methods, both provided by Apple, produce visibly different
> results.


They shouldn't produce visibly different results outside
minimal adaptions for the colour space ... you might be doing
something wrong. Maybe as easy as converting to Adobe RGB, but
not attaching that information to the image, so it gets shown as
sRGB (and looks somewhat washed out).

-Wolfgang
 
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me
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      01-02-2010
On Sat, 02 Jan 2010 10:39:12 -0800, isw <(E-Mail Removed)> wrote:


>I suppose, but I have no idea what. In both cases (one manual, one
>running an Applescript), it sure seems like the same thing should happen
>(I've looked inside the script, which controls the same app that I use
>to do the manual conversion).
>
>The difference between the output images seems to be no more than a
>change in levels, because I can make a simple adjustment to the "paler"
>one to make the two visually identical.


What options are you given in converting? In PS CS2 you are given the
Intent options of Perceptual, Saturation, Relative and Absolute
Colormetric and all but the Absolute Colormetric all you to choose
Black Point Compensation.
 
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