Re: Disabling colour management for a display
Re: Disabling colour management for a display
- Subject: Re: Disabling colour management for a display
- From: Charles D Tobie <email@hidden>
- Date: Sat, 05 Jan 2013 22:58:17 -0500
>>Let me first say that I'm appreciative of your input. Thank you.
For what it's worth...
>>I'm beginning to understand the problem at hand. I hope you don't mind if
I ask a few more questions just to gain a clearer understanding:
>>1) You said,
> If you are running a video stream through a video card to display, it
may
> or may not sidestep the VLUT data. It is common for this to happen under
Windows, but rare on the Mac.
>>Who or what determines whether the VLUT data is sidestepped: is it the OS,
the application, the profile in use or something else? Is it possible to
determine which applications are using the VLUT?
It's a mix. Depending on the card, and it's firmware, apps may or may not be able to sidestep the VLUTs. Some video software likes to do this, as they consider it to lower overhead.
>>2) You said,
> Using a profile with no VLUT data is the answer, so that no changes
occur
> to the raw RGB data you wish to send out.
>>What's the name of the tag(s) that would indicate the presence of a LUT?
I'm guessing it may be 'vcgt', but could you confirm?
Correct. Notice the Apple copyright on that tag...
>>3) You said,
> Selecting a generic
> profile such as sRGB will assure that there is no LUT data being applied
at the video card.
>>But what about changes made at the OS-level?
What changes being made at the OS level? Other than VLUT flashing, there should not be any. I admit, recent Mac OS versions appear to be doing things they should not, like limiting the gamut of secondary displays to the gamut of the main display, but in theory, there would not be any other meddling.
>> I suspect you're trying to
tell me that QuickTime, DVD Player, VLC etc. aren't ICC profile-aware, and
therefore aren't affected by OS-level colour management. Am I right?
Well, they certainly aren't applying a profile-based transform to very pixel of every frame run through them, based on an ICC profile; that would be massive overhead. But they may or may not be effected by the VLUT data in the video card, that came from an ICC profile, so in that sense they might be "affected" by color management.
>> If I'm wrong, then why is sRGB the best choice?
First, to avoid LUTs. But also because, at the OS level, there is some hidden voodoo about null conversions that sRGB sidesteps. Should not apply here, but it's still the safest bet with recent Mac OS versions.
>>Hopefully, answers to these should set me free to make some informed
decisions on the matter for the foreseeable future.
Best of luck.
C. David Tobie
Global Product Technology Manager
Imaging Color Solutions
Datacolor inc.
email@hidden
www.datacolor.com
On Jan 5, 2013, at 4:47 PM, email@hidden wrote:
> Let me first say that I'm appreciative of your input. Thank you.
>
> I'm beginning to understand the problem at hand. I hope you don't mind if
> I ask a few more questions just to gain a clearer understanding:
>
> 1) You said,
>> If you are running a video stream through a video card to display, it
> may
>> or may not sidestep the VLUT data. It is common for this to happen under
> Windows, but rare on the Mac.
>
> Who or what determines whether the VLUT data is sidestepped: is it the OS,
> the application, the profile in use or something else? Is it possible to
> determine which applications are using the VLUT?
>
> 2) You said,
>> Using a profile with no VLUT data is the answer, so that no changes
> occur
>> to the raw RGB data you wish to send out.
>
> What's the name of the tag(s) that would indicate the presence of a LUT?
> I'm guessing it may be 'vcgt', but could you confirm?
>
> 3) You said,
>> Selecting a generic
>> profile such as sRGB will assure that there is no LUT data being applied
> at the video card.
>
> But what about changes made at the OS-level? I suspect you're trying to
> tell me that QuickTime, DVD Player, VLC etc. aren't ICC profile-aware, and
> therefore aren't affected by OS-level colour management. Am I right? If
> I'm wrong, then why is sRGB the best choice?
>
> Hopefully, answers to these should set me free to make some informed
> decisions on the matter for the foreseeable future.
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