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Author Topic: Accurate Colors  (Read 33466 times)
tho_mas
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« Reply #40 on: July 14, 2009, 08:58:10 AM »
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Quote from: digitaldog
You sure about this?
with the quote completed ...
Quote
or so close that the eye would not notice the difference if the two were compared side by side (complicating operational factor: can the spectro actually measure accurately the colour of light reflected by these two very different kinds of materials?)
... I'd agree with Mark here.
Especially regarding "or so close that the eye would not notice the difference".
Maybe this could be a good intended use for the Colormunki with its UV cut filter (am not sure)...??
« Last Edit: July 14, 2009, 08:58:42 AM by tho_mas » Logged
digitaldog
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« Reply #41 on: July 14, 2009, 10:13:13 AM »
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Quote from: tho_mas
with the quote completed ...
... I'd agree with Mark here.
Especially regarding "or so close that the eye would not notice the difference".
Maybe this could be a good intended use for the Colormunki with its UV cut filter (am not sure)...??

There are a few potential issues. First is the illuminant used in the Spectrophotometer and the possible disconnect between the illuminate of the viewing conditions presented to the observer. Next there's the possibility of metameric failure or simultaneous contrast, a pretty common phenomena that cause the same color under the same illuminant to appear differently depending on the background color against which it is viewed. And again, we're assuming that taking a spot color reading of a complex image, and an associated spot reading on output, using CIE Lab colorimetry is going to tell us there's a match (rather than just looking at the two).

Bruce Fraser as usual, summed it up well and in a fashion that's easy to understand:

Quote
So while Lab is useful for predicting the degree to which two sets of
tristimulus values will match under very precisely defined conditions that
never occur in natural images, it is not anywhere close to being an adequate
model of human color perception. It works reasonably well as a reference
space for colorimetrically defining device spaces, but as a space for image
editing, it has some important shortcomings.

The viewing conditions for which Lab was designed will never exist in a
natural image. I repeat, Lab was designed to predict the degree of matching
between two solid color patches of a certain size on a neutral background.
Viewing conditions aren't just a matter of the illuminant, but also opf the
surround, and the spatial organization of the target colors. It's an
exaggeration to say that Lab describes colors. What Lab describes is
tristimulus values that, under the specified viewing conditions, will be
seen by the "standard observer" as colors. But when these tristimulus
values are located in a natural image, the perceived color is subject to
all the perceptual phenomena I've been mentioning, and the perceived color
may be quite different from what Lab predicts. If the color is
colorimetrically correct, but looks wrong, the image doesn't work.
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Andrew Rodney
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madmanchan
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« Reply #42 on: July 14, 2009, 10:14:07 AM »
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In general, creating these so-called "accurate" profiles is certainly possible, within limits. I say so, without defining the term accuracy, because for any reasonable definition of accurate, one can usually optimize the profile to meet the definition. However, the caveat is that the technical information required to build such a profile is usually not available, at least not easily, to end users. Ideally you would have spectral information regarding the scene characteristics (i.e., a set of spectral radiance samples of the scene you wish to photograph and reproduce) and spectral information about the optical system and sensor. The ColorSage solution referenced above is an example that has this, in a specific context (specific camera, specific scene); their overall methodology would generalize well to other contexts.
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Mark D Segal
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« Reply #43 on: July 14, 2009, 10:32:26 AM »
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Eric,

Thanks for clarifying this. What you saying seems to suggest that at this time it isn't possible to have a generic profile for use in a raw converter which will deliver "accurate" colour for just about any scene. Please correct me if I'm reading wrongly.

Andrew,

No, of course I'm not sure - that's why I used qualified language,    and yes, your quote from Bruce Fraser is indeed telling.

Mark
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Mark D Segal (formerly MarkDS)
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tho_mas
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« Reply #44 on: July 14, 2009, 10:37:11 AM »
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Quote from: digitaldog
There are a few potential issues. First is the illuminant used in the Spectrophotometer and the possible disconnect between the illuminate of the viewing conditions presented to the observer. Next there's the possibility of metameric failure or simultaneous contrast, a pretty common phenomena that cause the same color under the same illuminant to appear differently depending on the background color against which it is viewed. And again, we're assuming that taking a spot color reading of a complex image, and an associated spot reading on output, using CIE Lab colorimetry is going to tell us there's a match (rather than just looking at the two).

Bruce Fraser as usual, summed it up well and in a fashion that's easy to understand:
Thanks, Andrew.
I think that's basically clear.
But beside the limitations of colometric measurement there is still the criterion of visual perception. If you compare the reference artwork and the print you'd like them to match. Here it's not so essential that two colours match colormetric. The impression of "matching" is enough here.

Now the color measurement might be limited but at the same time it helps a lot in getting close to what is required. Sometimes very close (e.g. a Monitor and a print viewed under appropriate conditions can match very well though the display has backlight and the print has incident light).
Simplified: the closer you get with colormetric measurement the better. The rest is visual tweaking of colours and gradation in Photoshop.
And here I think icc profiles produced with e.g. "BasICColor Input" (trades under the name Color Eyes in the US, AFAIK) or similar products are a HUGE help to get close. If you say there is no matching based on colormetric measurement and therefore you don't need suitable input profiles I think this is a bit of a stretch (at least that's a bit how I am reading your comments - correct me if I'm wrong).
It is a fact that once you open an (Phase One DB) image in Capture One that it actually "reminds" you of the scene (the tradition of film conventions affect our perception as well, of course); maybe not "matching" by default, but not too far away. I once created a profile with "BC Input" and it was shocking how close the profile was to the reference. Problem here was: it was also shocking how unusable it was under different lighting conditions :-) This is why I stopped learning to create camera profiles and just use the Phase presets (Tungsten, Daylight, Outdoor Daylight, Flash ...) for my cameras. But for repro work I certainly would try it this way.
« Last Edit: July 14, 2009, 10:46:16 AM by tho_mas » Logged
digitaldog
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« Reply #45 on: July 14, 2009, 10:51:51 AM »
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Quote from: tho_mas
Simplified: the closer you get with colormetric measurement the better.
Again, not necessarily, maybe, sometimes.

Quote
The rest is visual tweaking of colours and gradation in Photoshop.
That's probably going to be necessary in many, many cases.

Quote
And here I think icc profiles produced with e.g. "BasICColor Input" (trades under the name Color Eyes in the US, AFAIK) or similar products are a HUGE help to get close.
Maybe. I think the idea that the input profile alone deserves sole credit here might be part science and part marketing. Clearly these profiles play an important role. But they can (and in some cases have) been over sold.

Quote
If you say there is no matching based on colormetric measurement and therefore you don't need suitable input profiles I think this is a bit of a stretch (at least that's a bit how I am reading your comments - correct me if I'm wrong).
That's not what I'm saying. I'm saying unless we know the entire processing path to the degree someone like Eric does in his product, we're all unqualified to say to what degree "accurate" color is produced solely by some input profile.

Quote
It is a fact that once you open an image in Capture One that it actually "reminds" you of the scene (the tradition of film conventions affect our perception as well, of course); maybe not "matching" by default, but not too far away.
Scene referred? Reminds you based on what? Did it record the illuminate of the scene and does it hold the spectral sensitivity of your chip in order to produce this report, or, it gives you the impression it knows about the scene? I don't know, I don't use that product but I'd be hard pressed to believe it has the necessary information that Eric and Robin are talking about ala ColorSage.

Its useful to at least attempt to separate the marketing hype or speak from the actual underlying functionality here. We've as yet not even defined the metric of "accurate" color here. Even if we use the term matching color, we need to agree that what matches for one observer may not for another, or in another environment. This is pretty complex stuff. But someone selling you a product can easily gloss over all this and just tell you "build a profile (ICC or otherwise) and you'll have accurate color. That raises the hair on the back of my neck every time I hear this.
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Andrew Rodney
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Czornyj
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« Reply #46 on: July 14, 2009, 11:08:26 AM »
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Quote from: madmanchan
In general, creating these so-called "accurate" profiles is certainly possible, within limits. I say so, without defining the term accuracy, because for any reasonable definition of accurate, one can usually optimize the profile to meet the definition. However, the caveat is that the technical information required to build such a profile is usually not available, at least not easily, to end users. Ideally you would have spectral information regarding the scene characteristics (i.e., a set of spectral radiance samples of the scene you wish to photograph and reproduce) and spectral information about the optical system and sensor. The ColorSage solution referenced above is an example that has this, in a specific context (specific camera, specific scene); their overall methodology would generalize well to other contexts.

Are the spectral information of camera sensors known to RAW converter developers? Or maybe the influence of various lenses to spectral sesitivity function is too significant?

Is it possible and effective to utilize spectral measurements of ambient light to create camera profiles for popular DSLR cameras?

Could the spectrophotometer become photographers best friend in the future?  Could it solve the AWB issue somehow?
« Last Edit: July 14, 2009, 11:11:54 AM by Czornyj » Logged

digitaldog
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« Reply #47 on: July 14, 2009, 11:12:50 AM »
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Quote from: Czornyj
Is it possible to utilize spectral measurements of ambient light to create camera profiles for popular DSLR cameras?

Could the spectrophotometer become photographers best friend in the future?  Could it somehow solve the AWB issue?

Yes and yes but it could be expensive. Eric Walowit who's on the ICC Digital Camera group has for years proposed the idea that our cameras would record the spectral properties of the scene, embed this as EXIF data with the Raw and, along with the important spectral sensitivity of the camera, build an on-the-fly profile for each image. It makes a lot of sense when technology affordable and dismisses Jack's idea about "one profile for all scenes" but that's admittedly based on the current and not very robust solutions offered today.
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Andrew Rodney
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tho_mas
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« Reply #48 on: July 14, 2009, 11:17:51 AM »
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Quote from: digitaldog
Reminds you based on what?
reminds me of the scene - the way I perceived it. I "accept" the colours and gradation as a photograph that represents something close to what I've seen.

I basically agree to the most of what you say. But whilst others define "accurate" we keep on photographing and I prefer input profiles that produce (howsoever) "useful" colours to start with. And I have yet to see that I open a RAW file in ACR/LR and it's by default close to the scene in some way (certainly depends on the camera... I don't know). That's what I don't get and my read is that at Adobe they share your standpoint that unless we can't do it really right, we cancel it all the way. Of course in C1 colours does not match "accurate" by default (how could they)... but you won't wonder about the colours you see (mostly) once you open a RAW file and set WB.

Quote
Its useful to at least attempt to separate the marketing hype or speak from the actual underlying functionality here. We've as yet not even defined the metric of "accurate" color here. Even if we use the term matching color, we need to agree that what matches for one observer may not for another, or in another environment. This is pretty complex stuff. But someone selling you a product can easily gloss over all this and just tell you "build a profile (ICC or otherwise) and you'll have accurate color. That raises the hair on the back of my neck every time I hear this.
I agree.
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Jack Flesher
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« Reply #49 on: July 14, 2009, 11:30:49 AM »
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Quote from: digitaldog
It makes a lot of sense when technology affordable and dismisses Jack's idea about "one profile for all scenes" but that's admittedly based on the current and not very robust solutions offered today.

Uh excuse me, but where did I ever indicate "one profile for all scenes" Huh  What I said above is a dedicated profile for a given set of lighting...

Here is what I said above:

Quote
Not really. It might perform reasonably well in brighter or dimmer values of the exact same temperature -- and why the Northlights are so good for repro -- but IME you want a dedicated profile for your standard copy sets.

Let me repeat that last part in BOLD: but IME you want a dedicated profile for your standard copy sets.

Cheers,
« Last Edit: July 14, 2009, 11:33:32 AM by Jack Flesher » Logged

digitaldog
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« Reply #50 on: July 14, 2009, 11:30:56 AM »
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Quote from: tho_mas
reminds me of the scene - the way I perceived it. I "accept" the colours and gradation as a photograph that represents something close to what I've seen.
Yes, that's nice but playing devils advocate, its again nearly impossible to say this is true or not. Its like those that want the print to match the display but don't have proper viewing conditions for viewing the print. They take the print to a number of locations away from display and while that lighting might be ideal, with out the display and print side by side, you're reduced to "memory" colors of what does or doesn't match. In the above discussion, we're at least talking about viewing a reproduction and the original under the same illuminant and asking if they match. Imagine if your client not took the fine art print home and said "it doesn't match" without having the original next to it (or a more common problem that might be impossible to fix, client finds that print and painting under different illuminate now do not match when they did in your studio).

Getting back to accurate, its by definition in a measurable way, the scene referred capture and by the time the Raw converter renders an output referred preview on screen, its just impossible to say its accurate or a match. In the ICC article link above, the reasons are explained.

Quote
And I have yet to see that I open a RAW file in ACR/LR and it's by default close to the scene in some way (certainly depends on the camera... I don't know). That's what I don't get and my read is that at Adobe they share your standpoint that unless we can't do it really right, we cancel it all the way. Of course in C1 colours does not match "accurate" by default (how could they)... but you won't wonder about the colours you see (mostly) once you open a RAW file and set WB.
Now we have to investigate if this problem is solvable using either or both custom or tweaked DNG profiles or preset rendering adjustments. Its possible this isn't possible. Its possible C1 produces a more preferable match by default (there have been lots of users who complain about the default ACR rendering as such, the defaults have been tweaked over the years. You can't please all the people all the time). I'm not disagreeing with your findings here. I prefer the default rendering of Raw Developer and taking color and tone out of the mix, there's just some Raw processing that I find preferable that no amount of profile or rendering tweaking in ACR will match.
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Andrew Rodney
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« Reply #51 on: July 14, 2009, 11:31:33 AM »
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Quote from: Jack Flesher
Uh excuse me, but where did I ever indicate "one profile for all scenes" Huh  What I said above is a dedicated profile for a given set of lighting...

Other Jack. See above.
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Andrew Rodney
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« Reply #52 on: July 14, 2009, 11:31:52 AM »
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Quote from: digitaldog
Yes and yes but it could be expensive. Eric Walowit who's on the ICC Digital Camera group has for years proposed the idea that our cameras would record the spectral properties of the scene, embed this as EXIF data with the Raw and, along with the important spectral sensitivity of the camera, build an on-the-fly profile for each image. It makes a lot of sense when technology affordable and dismisses Jack's idea about "one profile for all scenes" but that's admittedly based on the current and not very robust solutions offered today.

Thanks Andrew - I know many wedding photographers, that would definitely like Eric's idea - even if they had to pay a fortune and mount a ColorMunki (or even i1pro) on top of their cameras...

Now I'll patiently wait for i1pro support in DNG Profile Editor
« Last Edit: July 14, 2009, 11:32:56 AM by Czornyj » Logged

Jack Flesher
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« Reply #53 on: July 14, 2009, 11:34:03 AM »
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Quote from: digitaldog
Other Jack. See above.

Duh.  Sorry  
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« Reply #54 on: July 14, 2009, 11:37:14 AM »
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Quote from: Jack Flesher
Duh.  Sorry  

I should have been more clear. No worries.
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Andrew Rodney
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« Reply #55 on: July 14, 2009, 11:52:02 AM »
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Quote from: digitaldog
Yes, that's nice but playing devils advocate
but at the current state of colormanagement it's sometimes all we can do :-) A friend of mine is a prepress guy and they do a lot of shots for sports products... all synthetics of course (okay, nasty). It's impossible to measure the (product-) colours under D50 or even under D65. No way. He takes the products, goes out of the office and eye up the stuff under daylight in different conditions. Then he tweakes the colours from memory.
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« Reply #56 on: July 14, 2009, 04:48:00 PM »
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And using a printer profile built on one rip won't work on another so I guess I don't see the point.
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Jack Bingham
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« Reply #57 on: July 15, 2009, 12:22:17 AM »
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Yes, Mark, you understood me correctly. Camera profiles are generally built with a set of assumptions in mind. Being pre-baked, without detailed knowledge of the photographer and his/her preferences, the scene content to be photographed, or the illumination to be used, the assumptions can only go so far. The strength of the ColorSage solution is that many of the variables are removed: information about the surface characteristics, the lighting used to capture the image, the lighting used to reproduce the image, and the characteristics of the optical system are all provided. For most general purpose photography, such detailed information is not always available, though the steps proposed by Eric Walowit (outlined by Andrew) are in the right direction.

This is one reason why most cameras provide multiple rendering presets selectable from the menu options, with names like Standard, Neutral, Natural, Vivid, Portrait, Landscape, Monochrome, Faithful, etc. Even assuming detailed scene characteristics are available, the camera designers know that photographers will simply have different individual preferences and cannot predict for a given exposure how the user will want to render that image.

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Mark D Segal
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« Reply #58 on: July 15, 2009, 06:18:50 AM »
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Thanks for the confirmation Eric.

So many variables - like peeling an artichoke - you can keep going till you get down to the core, by which time the problem is reduced to a very small manageable set of conditions which can be targeted and programmed for predictable, controlled outcomes. For a great many uses of photography that simply isn't necessary, and for those needing it - well they can peel the artichoke and craft their presets accordingly. So in this context, one of the most important characteristics of raw conversion software becomes its ability to respond flexibly to different needs, and from what I observe, that is the direction in which LR/ACR have been moving.
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Mark D Segal (formerly MarkDS)
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« Reply #59 on: July 15, 2009, 07:28:19 AM »
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Quote from: MarkDS
So in this context, one of the most important characteristics of raw conversion software becomes its ability to respond flexibly to different needs, and from what I observe, that is the direction in which LR/ACR have been moving.

...but some kind of illuminant's spectral data utilization in DNG Profile Editor would also be nice...
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