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"Assigning" vs. "Matching" a color profile



 
 
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  #1  
Old December 28th 09, 08:11 PM posted to rec.photo.digital
isw
external usenet poster
 
Posts: 212
Default "Assigning" vs. "Matching" a color profile

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?

Isaac
  #2  
Old December 28th 09, 08:33 PM posted to rec.photo.digital
nospam
external usenet poster
 
Posts: 24,165
Default "Assigning" vs. "Matching" a color profile

In article ], isw
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.


iphoto does weird things with colour profiles. use something else if
possible.

what profile did the scanner give 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).


assign means just that, you are assigning a profile to an image, which
says 'this data is in profile z.' the data is not changed, it just
tells the system how to interpret the data. if you assign a different
profile, your image will look different.

match is probably the same as what photoshop calls convert to, and it
means it will take the existing data and convert that data to a new
profile, using the assigned profile as a source profile, if any. the
data will be changed and the image should look roughly the same,
subject to any limitations in the destination profile.

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?


pun intended?
  #3  
Old December 28th 09, 10:38 PM posted to rec.photo.digital
isw
external usenet poster
 
Posts: 212
Default "Assigning" vs. "Matching" a color profile

In article ,
nospam wrote:

In article ], isw
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.


iphoto does weird things with colour profiles. use something else if
possible.


Not possible. Plus, what I've been able to understand from reading about
iPhoto and profiles is that honoring profiles is a *good* thing for
color accuracy.

what profile did the scanner give it?


Microtek 4800 Scanner / Positive Film / Present

Why that annoys iPhoto I don't know, but the result is that when I
import an image bearing that profile, the thumbnail winds up being a
black rectangle. I suppose it's possible that there's some aspect of
that profile that is "wrong" somehow, but I have no way to fix it, so
just eliminating it seems like a good solution.

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).


assign means just that, you are assigning a profile to an image, which
says 'this data is in profile z.' the data is not changed, it just
tells the system how to interpret the data. if you assign a different
profile, your image will look different.


Ah. Then using "assign" to get rid of the problematical profile sounds
like a mistake, since the result would be that the profile would be
"lying" about the image. I'd guess you'd use "assign" if you knew what
an image's profile *should* be, but that's not what was in the metadata.

match is probably the same as what photoshop calls convert to, and it
means it will take the existing data and convert that data to a new
profile, using the assigned profile as a source profile, if any. the
data will be changed and the image should look roughly the same,
subject to any limitations in the destination profile.


So if I do not want to change the appearance but I *do* want to change
the profile, "match" sounds like the way to go.

Now, what is a good profile to move to, assuming I want the widest
reasonable color gamut on CRT or flat-panel displays but NOT involving
the web or browsers? (What I mean is, showing my images to friends and
relatives on a computer or digital TV).

I *think* I understand that sRGB is a rather limited gamut, for example.
What about ProPhoto? Using colorSync Utility, it seems to be nearly the
only gamut that's larger than the scanner's.

Isaac
  #4  
Old December 28th 09, 11:54 PM posted to rec.photo.digital
nospam
external usenet poster
 
Posts: 24,165
Default "Assigning" vs. "Matching" a color profile

In article ], isw
wrote:

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.


iphoto does weird things with colour profiles. use something else if
possible.


Not possible. Plus, what I've been able to understand from reading about
iPhoto and profiles is that honoring profiles is a *good* thing for
color accuracy.


it's a very good thing, except iphoto doesn't quite do it right.

what profile did the scanner give it?


Microtek 4800 Scanner / Positive Film / Present

Why that annoys iPhoto I don't know, but the result is that when I
import an image bearing that profile, the thumbnail winds up being a
black rectangle. I suppose it's possible that there's some aspect of
that profile that is "wrong" somehow, but I have no way to fix it, so
just eliminating it seems like a good solution.


that's worse than i thought. usually the colours are a little off if
it's the wrong profile, not black.

there's a profile first aid check in color sync utility - what does
that say? what happens if you try other software, such as photoshop,
preview, or even safari?

Ah. Then using "assign" to get rid of the problematical profile sounds
like a mistake, since the result would be that the profile would be
"lying" about the image. I'd guess you'd use "assign" if you knew what
an image's profile *should* be, but that's not what was in the metadata.


except if that profile is corrupt or the software you are using is
buggy. if another profile makes it look better, what difference does it
make? after all, that's what matters not what is technically 'correct.'
although the correct profile should be the one that looks the best,
that's not always the case.

Now, what is a good profile to move to, assuming I want the widest
reasonable color gamut on CRT or flat-panel displays but NOT involving
the web or browsers? (What I mean is, showing my images to friends and
relatives on a computer or digital TV).


for showing on a screen, srgb is probably fine. do your friends have
expensive eizo lcd displays that can display adobe rgb? probably not.
if their displays can only show srgb, why bother using something wider?

I *think* I understand that sRGB is a rather limited gamut, for example.
What about ProPhoto? Using colorSync Utility, it seems to be nearly the
only gamut that's larger than the scanner's.


srgb is fine for most things, but if you really want to edge out the
absolute best, you want adobe rgb or better, however, once it's
scanned, you aren't going to gain much by picking a wider space.
  #5  
Old December 29th 09, 05:24 AM posted to rec.photo.digital
isw
external usenet poster
 
Posts: 212
Default "Assigning" vs. "Matching" a color profile

In article ,
nospam wrote:

In article ], isw
wrote:

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.

iphoto does weird things with colour profiles. use something else if
possible.


Not possible. Plus, what I've been able to understand from reading about
iPhoto and profiles is that honoring profiles is a *good* thing for
color accuracy.


it's a very good thing, except iphoto doesn't quite do it right.

what profile did the scanner give it?


Microtek 4800 Scanner / Positive Film / Present

Why that annoys iPhoto I don't know, but the result is that when I
import an image bearing that profile, the thumbnail winds up being a
black rectangle. I suppose it's possible that there's some aspect of
that profile that is "wrong" somehow, but I have no way to fix it, so
just eliminating it seems like a good solution.


that's worse than i thought. usually the colours are a little off if
it's the wrong profile, not black.

there's a profile first aid check in color sync utility - what does
that say? what happens if you try other software, such as photoshop,
preview, or even safari?


ColorSync doesn't complain, nor do other apps, except to ask if it
should be converted. iPhoto displays the full-sale image just fine too;
it's just the thumbnail that's black. Real problem is, when I delete
those images so I can change the profile and reimport, then emptying the
iPhoto trash almost always causes a crash, and sometimes requires a
database rebuild, which takes several hours.

Ah. Then using "assign" to get rid of the problematical profile sounds
like a mistake, since the result would be that the profile would be
"lying" about the image. I'd guess you'd use "assign" if you knew what
an image's profile *should* be, but that's not what was in the metadata.


except if that profile is corrupt or the software you are using is
buggy. if another profile makes it look better, what difference does it
make? after all, that's what matters not what is technically 'correct.'
although the correct profile should be the one that looks the best,
that's not always the case.


I understand that, but I also *think* I understand that once an image
has been shoehorned into a limited color gamut, there's no way to
recover what's been lost.

Now, what is a good profile to move to, assuming I want the widest
reasonable color gamut on CRT or flat-panel displays but NOT involving
the web or browsers? (What I mean is, showing my images to friends and
relatives on a computer or digital TV).


for showing on a screen, srgb is probably fine. do your friends have
expensive eizo lcd displays that can display adobe rgb? probably not.
if their displays can only show srgb, why bother using something wider?


Because I expect that in future, even commodity displays are going to
have a wider gamut than present-day high-end ones; don't you?

I *think* I understand that sRGB is a rather limited gamut, for example.
What about ProPhoto? Using colorSync Utility, it seems to be nearly the
only gamut that's larger than the scanner's.


srgb is fine for most things, but if you really want to edge out the
absolute best, you want adobe rgb or better, however, once it's
scanned, you aren't going to gain much by picking a wider space.


According to ColorSync Utility, the existing profile (Microtek 4800
Scanner), is considerably larger then either sRGB or AdobeRGB, but
smaller than ProPhoto. What I'm interested in, is not throwing anything
away that might be valuable later, say on next-generation displays.
These are family images I'm preparing for my kids; they may well be
viewed in 50 years or more.

Isaac
  #6  
Old December 29th 09, 05:59 PM posted to rec.photo.digital
me[_5_]
external usenet poster
 
Posts: 578
Default "Assigning" vs. "Matching" a color profile

On Mon, 28 Dec 2009 11:11:08 -0800, isw 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)
  #7  
Old December 29th 09, 06:45 PM posted to rec.photo.digital
isw
external usenet poster
 
Posts: 212
Default "Assigning" vs. "Matching" a color profile

In article ,
me wrote:

On Mon, 28 Dec 2009 11:11:08 -0800, isw 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)


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?

ISaac
  #8  
Old December 29th 09, 08:28 PM posted to rec.photo.digital
me[_5_]
external usenet poster
 
Posts: 578
Default "Assigning" vs. "Matching" a color profile

On Tue, 29 Dec 2009 09:45:48 -0800, isw 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.
  #9  
Old December 30th 09, 05:31 AM posted to rec.photo.digital
isw
external usenet poster
 
Posts: 212
Default "Assigning" vs. "Matching" a color profile

In article ,
me wrote:

On Tue, 29 Dec 2009 09:45:48 -0800, isw 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.


It is my understanding (which may be incorrect), that when an image is
"matched" to a different profile, the values of the pixels are
"corrected" to agree with the new profile. If that is so, then once an
image is "matched" to a low-gamut profile like sRGB, then it's not
possible to recover the lost information, even in theory.

Can iPhoto show out of gamut colors? You could then see
what colors are contained/maintained in a given color space.


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.

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.

Isaac
  #10  
Old December 30th 09, 05:27 PM posted to rec.photo.digital
MikeWhy
external usenet poster
 
Posts: 78
Default "Assigning" vs. "Matching" a color profile

"isw" wrote in message
]...
In article ,
me 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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