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Author Topic: What actually happens during Calibration?  (Read 3248 times)

Rob C

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Re: What actually happens during Calibration?
« Reply #40 on: March 25, 2017, 07:08:57 PM »

Aaron,

I do have a machine with Vista installed, that I'd bought because I wanted to keep the XP solely for photography, disconnected from, and not at risk of itself getting screwed via the Internet. Consequently, the newer Vista machine was used for communication with the great out-there, though I did try to load PS6 into it, off the CD, but it wouldn't take PS6. Thus, I never tried the calibration device with it either. But it became very slow, and still is when I use it sometimes for old-time's sake. I get a notice telling me the battery is very low... The W8.1  now does the lot: photography and communication - I stopped being scared as I keep the important stuff that I can on a pair of external drives just in case!

Regarding the newer computer with Windows 8.1, when it arrived I was horrified: I couldn't work it at all, the desktop and everything to do with it was totally alien. Somebody on LuLa did me a great service and told me about Classic Shell, which I could download and would convert the system to 'look' like an older model of computer, and that's what made the thing workable for me. However, sometimes, if the pointer is swung off to the extreme right, up pops the damned original 8.1 interface untiil I move rapidly back across the screen. For a long time Microsoft was offering free upgrade to W 10 but I refused to bite: I was scared about what the hell next would become incompatible.

Now here's a question: is it possible to copy an entire C drive onto a second, spare C drive and thus have a working copy of everything, including one's version of Photoshop? I ask, because I've heard that solid drives are more likely to pack up than the old-fashioned type I have in the old computers. It would be reassuring to think that, in a disaster, I could simply have the drives replaced without losing anything and all the trouble involved in getting it all anew. Now you understand why I have no worries about feeling 'talked down' to: it's impossible. I do pictures, and not a lot beyond that.

;-)

Rob

Mark D Segal

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Re: What actually happens during Calibration?
« Reply #41 on: March 25, 2017, 07:19:47 PM »


Now here's a question: is it possible to copy an entire C drive onto a second, spare C drive and thus have a working copy of everything, including one's version of Photoshop? I ask, because I've heard that solid drives are more likely to pack up than the old-fashioned type I have in the old computers. It would be reassuring to think that, in a disaster, I could simply have the drives replaced without losing anything and all the trouble involved in getting it all anew. Now you understand why I have no worries about feeling 'talked down' to: it's impossible. I do pictures, and not a lot beyond that.

;-)

Rob



Rob, I'm not Aaron, but I was a Windows user till 2010 when I left it for good. At the time I used "Acronis", which provides a complete disk imaging solution for Windows operating systems. I believe it is still prominent. A disk image is essentially your whole computer on another drive.
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Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....." http://www.luminous-landscape.com/reviews/film/scanning_workflows_with_silverfast_8.shtml

Doug Gray

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Re: What actually happens during Calibration?
« Reply #42 on: March 25, 2017, 07:51:22 PM »

I use windows 10 on most of my computers. It's pretty robust and all my apps work find on it. I also use Win 7 and XP for some really old stuff on a virtual system.

Making an image copy of any disk is pretty easy and Win 10 can mount them where they just look like another drive or you can create VHDs for backup. I have several rotating USB drives for that.

https://msdn.microsoft.com/en-us/library/windows/desktop/dd323654(v=vs.85).aspx
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aaron125

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Re: What actually happens during Calibration?
« Reply #43 on: March 25, 2017, 07:53:20 PM »

Absolutely - Acronis True Image is still the premier backup and imaging app for Windows users. It makes the fastest and smallest images of hard drives when compared against other prominent backup apps.


Sent from my iPhone using Tapatalk
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Rand47

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Re: What actually happens during Calibration?
« Reply #44 on: March 26, 2017, 04:18:40 PM »

Absolutely - Acronis True Image is still the premier backup and imaging app for Windows users. It makes the fastest and smallest images of hard drives when compared against other prominent backup apps.


Sent from my iPhone using Tapatalk

Acronis is fine as long as you never try to remove it.  I could tell you a pretty good horror story about that.

Rand
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Rand Scott Adams

Pictus

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Re: What actually happens during Calibration?
« Reply #45 on: March 27, 2017, 10:20:39 AM »

I used Acronis for years, but Macrium's Rapid Delta Restore(RDR)
https://blog.macrium.com/2015/03/17/focus-on-macriums-rapid-delta-restore-rdr-3/
convinced-me. (The free version does not have this feature.)
Macrium is also more friendly to the operational system...
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Doug Gray

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Re: What actually happens during Calibration?
« Reply #46 on: March 29, 2017, 01:46:26 AM »

You are perhaps adding to the confusion. The ICC profile comes from the characterization, not the calibration, though the same software handles both.

Perhaps it's a bit pedantic but characterization can be stored in either the ICC profile, typically in the VCGT tag, or the monitor. The data in the VCGT is loaded into the video card LUTs but is otherwise unused in color management. When the monitor characterization data is stored in the profile's VCGT, it remaps the RGB values in an 8 bit system to ones that result in the desired RGB response. The rest of the profile contains that response as well as the xy coordinates of the RGB colors adapted to D50 and the XYZ values of the white point which is often not D50.

When the characterization data is stored in the monitor, the only portion of this stored in the ICC profile is, typically, only the RGB primary xy coordinates and white point info. For best coverage one choses native for these and the profile then is set for the maximum possible color gamut.

One can even use a standard colorspace, such as sRGB or Adobe RGB if the monitor's color gamut encompasses it. Then the system can be set for the monitor to use that working space.

There are some monitors with built in colorimeters that can be set up to automatically re-calibrate/characterize the monitor to a standard working space. those monitors contain the entire characterization data within the monitor.
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GWGill

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Re: What actually happens during Calibration?
« Reply #47 on: March 29, 2017, 07:19:02 AM »

Perhaps it's a bit pedantic but characterization can be stored in either the ICC profile, typically in the VCGT tag, or the monitor.
No - that's not characterization, that's calibration. It represents a transformation from some desired per channel response to the native per channel response.
Characterization (i.e. profile) data is stored in the ICC profile proper, as a matrix or cLUT data, and doesn't represent any particular transformation of the device behavior.

Displays with color management hardware may allow either per channel calibration curves or colorspace emulation. In neither case is characterization data send to the hardware.
« Last Edit: March 29, 2017, 07:23:00 AM by GWGill »
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Simon Garrett

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Re: What actually happens during Calibration?
« Reply #48 on: March 29, 2017, 08:18:04 AM »

No - that's not characterization, that's calibration. It represents a transformation from some desired per channel response to the native per channel response.
Characterization (i.e. profile) data is stored in the ICC profile proper, as a matrix or cLUT data, and doesn't represent any particular transformation of the device behavior.

Displays with color management hardware may allow either per channel calibration curves or colorspace emulation. In neither case is characterization data send to the hardware.

That's my understanding too.

The three 1-dimension tables in the video card (the Video Card Gamma Tables - VCGT) are used to map the tone curve to a specific curve (typically a gamma curve) and set the colour temperature.  They can't alter the colour space that the monitor displays.  That requires a 3D transformation - usually done in monitors that support this - to map RGB values from one colour space to another.  Clearly a monitor is limited in what it can display by the dyes or phosphors in the screen, but potentially a monitor can emulate any colour space that is entirely contained within its native colour space.  This means that wide-gamut monitors, that typically have a colour space of about Adobe RGB or perhaps a bit wider, can emulate sRGB.  An sRGB monitor can't emulate anything except sRGB or something narrower still.

When one calibrates and profiles a monitor, the software does two things, and then puts the resulting information into a newly-created profile:
  • The software calibrates the display - adjusts the tone curve (e.g. to a 2.2 gamma) and white point (e.g. to 6500K) by means of generating a Look Up Table.  This information is loaded into the vcgt field of the profile (though technically it isn't profile information).
  • The software then characterises (profiles) the display by measuring the tone curve, white point, colour space etc, and putting the resulting measurement into the profile.

When the computer boots up, software reads the profile, extracts the vcgt info and loads it into the video card, which henceforth adjusts all video information sent to the monitor.  All programs - whether colour-managed or not - benefit from the adjusted tone curve and white point. 

Colour managed programs (only) read the profile for colour space info, and map colours from image colour space to the monitor's colour space (as recorded in the profile) for display.  Only colour managed programs will get the right colours (because other programs don't map colours to the monitor's colour space).

For those more advanced monitors with internal 3-D LUTs that can emulate colour spaces other than their native colour space, the calibration/profiling software also creates a colour space mapping table during calibration, and that is loaded into the monitor.  Again, all programs will "see" that emulated colour space (but non colour-managed programs won't necessarily get the right colours unless the image colour space happens to be the same as the colour space the monitor is emulating).
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Doug Gray

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Re: What actually happens during Calibration?
« Reply #49 on: March 29, 2017, 10:40:48 AM »

No - that's not characterization, that's calibration. It represents a transformation from some desired per channel response to the native per channel response.
Characterization (i.e. profile) data is stored in the ICC profile proper, as a matrix or cLUT data, and doesn't represent any particular transformation of the device behavior.
Displays with color management hardware may allow either per channel calibration curves or colorspace emulation. In neither case is characterization data send to the hardware.
Is this a correct interpretation?

The characterization data results from a process and becomes part of the profile, producing transforms available to the color management software. The use of that profile on any system with a monitor in an identical state of calibration would produce the same displayed image.

Device calibration is normally described as that which is only done within the device itself to place it into a known state. The "calibration" data, when stored in the VCGT, is special. It is, in a sense, calibration that is offloaded to piggyback on the monitor's ICC profile.  It doesn't participate in color management software. I don't really like to think of this as "calibration" because it isn't something that travels with the monitor. One may consider VCGT tables as sui generis.

However, that same information could, instead, be stored within the color management profile tables and not use VCGT modification at all. Then it is visible to the color software and can be properly called characterization data.

Alternately, the information, specific to that monitor, could be stored internally by the monitor and hence becomes calibration. It travels with the monitor.
« Last Edit: March 29, 2017, 11:47:08 AM by Doug Gray »
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Tim Lookingbill

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Re: What actually happens during Calibration?
« Reply #50 on: March 29, 2017, 02:07:10 PM »

The VCGT as I've understood it since my first Mac in '98 and explained in my previous response in this thread tweaks each RGB curve in order to neutralize the entire black to white gray scale as it is defined (XYZ) by what the colorimeter measures of the displays actual native color of white which may be on the green or magenta side of a 6500K standard.

This explains why on my old fluorescent backlit Dell if I chose a target 6500K instead of native the VCGT RGB curves would be a lot more distorted and my white would turn a bit pinkish. These tweaks to this VCGT are not to be taken lightly especially the green channel which you can emulate tweaking in Photoshop's point curve. The green channel greatly influences overall density and gamma contrast appearance and is very sensitive to subtle adjustments which play a larger role in controlling banding of gradients within the VCGT especially on 8 bit video cards.

So if your native white that can't be seen by eye what exact color it is, better be pretty damn neutral because if the colorimeter sees too much green (that you can't see) in the white typical of native states of some fluorescent backlit displays then there's the likelihood you're going to get banding relying on VCGT on an 8 bit video card.

Calibrating neutrality in higher bit hardware LUT displays don't have this problem I'm guessing. For my 8bit video VCGT I painstakingly make sure the white of my display is as neutral as possible slightly tweaking my display's RGB gains.
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GWGill

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Re: What actually happens during Calibration?
« Reply #51 on: March 29, 2017, 09:16:45 PM »

Is this a correct interpretation?
Yes it is.
Quote
The characterization data results from a process and becomes part of the profile, producing transforms available to the color management software. The use of that profile on any system with a monitor in an identical state of calibration would produce the same displayed image.
Unfortunately it's not clear whether you are referring to the (non-ICC) VCGT tag, or the ICC profile. If the latter, then no - the transforms the profile contains are from/to PCS (i.e. device independent CIE) colorspace, so the device profile sets no targets, and by itself is not capable of producing a particular displayed image. In fact it is not the device profile that determines what the image will look like, it is the source device profile that must be linked with the destination display profile that determines this.
Quote
Device calibration is normally described as that which is only done within the device itself to place it into a known state. The "calibration" data, when stored in the VCGT, is special. It is, in a sense, calibration that is offloaded to piggyback on the monitor's ICC profile.  It doesn't participate in color management software. I don't really like to think of this as "calibration" because it isn't something that travels with the monitor. One may consider VCGT tables as sui generis.
Yes. It is used to transform the behavior of the display into a calibrated state. This is the difference between calibration and characterization. Calibration is done relative to a desired response, Characterization has no desired response. The mechanisms to store and implement the calibration are irrelevant - it just happens that it is the video display card that always has per channel curves, so some mechanism to save this state on the computer is logical. The fact that the profile depends on the display being in a particular calibration state also makes it useful that the profile can contain the calibration curves, so that the calibration state and matching profile will switch together.
Quote
However, that same information could, instead, be stored within the color management profile tables and not use VCGT modification at all.
Yes - but (ignoring ICC V4 absolute colorimetric intent madness) that is exactly the same as profiling the display without calibration curves applied.
i.e. it is only that fact that the VCGT curves are applied outside profiling and the application of the profile, that makes them affect the profiling data.
Quote
Then it is visible to the color software and can be properly called characterization data.
Actually it is the opposite - it is then invisible to the color software and may as well not exist. But if the poor state of ICC absolute display colorimetry is taken into account. it does form a useful purpose either way in changing the white point and improving the display behavior by  modifying the display behavior in more detail than a profile can conveniently achieve.
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Simon Garrett

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Re: What actually happens during Calibration?
« Reply #52 on: March 30, 2017, 04:31:58 AM »

However, that same information could, instead, be stored within the color management profile tables and not use VCGT modification at all.  Then it is visible to the color software and can be properly called characterization data. 
Actually it is the opposite - it is then invisible to the color software and may as well not exist. But if the poor state of ICC absolute display colorimetry is taken into account. it does form a useful purpose either way in changing the white point and improving the display behavior by  modifying the display behavior in more detail than a profile can conveniently achieve.

Agreed.  Another useful purpose of having a calibrated monitor (rather than characterising/profiling the monitor in an uncalibrated state) is that non colour-managed programs will benefit from the calibrated tone curve and white point.  As you say, it makes little difference to colour-managed software.

I think it can also help to get the monitor in roughly the right state by manual controls (or automatic display control, if monitor and calibration software support that).  That minimises the arithmetic rounding errors that can arise with LUTs. 
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Alan Goldhammer

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Re: What actually happens during Calibration?
« Reply #53 on: March 31, 2017, 01:28:44 PM »


Now here's a question: is it possible to copy an entire C drive onto a second, spare C drive and thus have a working copy of everything, including one's version of Photoshop? I ask, because I've heard that solid drives are more likely to pack up than the old-fashioned type I have in the old computers. It would be reassuring to think that, in a disaster, I could simply have the drives replaced without losing anything and all the trouble involved in getting it all anew. Now you understand why I have no worries about feeling 'talked down' to: it's impossible. I do pictures, and not a lot beyond that.

;-)

Rob
I don't know what the term "pack up" means.  If it means "drive failure" that is incorrect as solid state drives are far more reliable than mechanical drives.  There are a number of software approaches to protecting yourself from disaster.  Some were mentioned by other posters.  I happen to use the one that came with NovaBackup which I use as my cloud storage solution.  It has a disaster recovery program built in that can restore everything pretty easily.

Addressing your original question about the LaCie colorimeter, it is their responsibility to make sure that it is compatable with future software operating systems.  Any disc you have contains drivers that are very old and that's why it won't work with Windows 8.1 (BTW, I've been running 8.1 for over a year now and it's has been rock solid stable.  I got this version for my new workstation; the old one ran Win7.)  You need to look on line to see if you can find the new driver.  It may be that this is old technology that LaCie is no longer supporting in which case you are out of luck.
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adias

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Re: What actually happens during Calibration?
« Reply #54 on: April 18, 2017, 02:38:41 PM »

To summarize, there's:

Display Calibration - define display contrast, white balance, brightness set points - either done on the display or the video card. The latter more often. If the calibration is done in the video card different calibration parameters must be used for different screens.

Display Profiling - a set of mapping curves [look-up-tables (LUTs) or a simple matrix set] for the primary colors to correct display deviations from a desired contrast (gamma) curve.

For those who use monitor calibration tools (sensor + software) both calibration and profiling are taken care by that system implementation.

Simon Garrett

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Re: What actually happens during Calibration?
« Reply #55 on: April 18, 2017, 05:29:10 PM »

To summarize, there's:

Display Calibration - define display contrast, white balance, brightness set points - either done on the display or the video card. The latter more often. If the calibration is done in the video card different calibration parameters must be used for different screens.

Yes that's part of it.

Display Profiling - a set of mapping curves [look-up-tables (LUTs) or a simple matrix set] for the primary colors to correct display deviations from a desired contrast (gamma) curve.

No, this is also part of calibration.  The LUTs that alter the Tone Response Curve to a defined curve (typically a gamma curve) are loaded in the video card's gamma table (VCGT) in a combined table that also deals with white point and so on. 

Tone Response Curve affects the contrast; there's no specific "contrast" calibration.


For those who use monitor calibration tools (sensor + software) both calibration and profiling are taken care by that system implementation.

Profiling is another stage after calibration, and in that stage the monitor's colour space is measured (not altered).  The TRC and white point are also measured.  That measurement goes in the profile (along with the LUT data for the VCGT, although strictly VCGT info is not really part of the profile - it just goes in the same file for convenience). 

When the system boots up, a utility looks up the profile, extracts the vcgt field, and loads it into the VCGT in the video card.  This affects all information sent to the card, so all programs, whether colour-managed or not, get the corrected white point and tone response curve.

The profile information is used only by colour-managed programs, which use the profile to map colours from the image's colour space (sRGB, Adobe RGB or whatever) into the monitor's colour space (as measured during the profiling stage, and unique to that monitor). 
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