Color managment - Please sticky if worthy

Started Mar 29, 2013 | Discussions
fft81
Contributing MemberPosts: 896
Like?
Color managment - Please sticky if worthy
Mar 29, 2013

COLOR MANAGEMENT- CAMERA TO MONITOR AND PRINTER

This document is meant as a short and right to the point write-up about color management. There are 3 things that photographer has to work with that need to be profiled, Camera, Monitor and Printer. One big misconception is that they are being calibrated to match each other. In reality, they are all calibrated to match color codes in a standard color set. By all matching the same color set they also match each other. Therefore we can talk about calibrating the camera, monitor and printer sparely, but to the same standard.

Camera

The sensor in the camera interprets colors differently, varying from onecamerato another and it even interprets colors differently depending onambient light. Camera’s white balance feature is meant to compensate for certain cases of lighting conditions, but white balance is just an approximation. One can use color checker to establish known colors and then in software factor out the lighting and camera effects from the final image. In reality, camera measures intensity of red, green and blue light falling on the sensor. Then by making a guess about the energy spectrum of ambient light the camera interprets the measured RGB intensities to determine what color to assign to a given pixel. RAW file records intensity measured by each pixel, JPG uses white balance setting to record cameras guess of color of each pixel based on white balance setting you chose. By taking photograph of color checker one can create a much more accurate correlation between the intensity of light that each pixel measured and the color of that pixel in post-production software. The end goal is to have the color values of the output picture match the color values of the object you photographed. You can think of it this way, each color in real life has a value; camera sees light reflected off that object and records the value which is the sum of values of incident light and color value of the object. Using color checker you can calculate the color value of incident light, subtract it from recorded value and end-up with true color value of the object you photographed.

Printer

Now that you have a file in your computer, the color values within which match the color values of the object, you need to be able to reproduce those colors on paper through your printer. How printed colors look is effected by yourprinter, ink set your printer uses, the paper your printer usesand the lighting conditions of the area when you view the print. Usually you cannot predict lighting conditions of where the print will be viewed, so printer profiling only takes into account the ink and paper combination. By printing a set of color patches the calibrating device like colormunki knows how colors should look like on paper and by measuring the printed patches colormunki knows how they actually look. As the result colormunki can generate a correction table, which is called ICC profile, which the print driver uses to print colors more accurately. For example if RGB value of a patch to be printed is 134-126-231 but the measured value of printed patch is 120-110-254, then the driver knows that when it wants to print 120-110-254 it needs to tell the printer to print 134-126-231. Most stock/canned profiles supplied by printer manufacturer will be more accurate that profiles you can generate with colormunki, but they are only available for OEM inks and limited number of papers. Hence you can use CM to make profiles for printer-ink-paper combinations that OEM maker does not provide.

Monitor

Biggest advantage of color calibrator like ColorMunki is that it can calibrate your monitor. This will let you see colors that are a close match to what you print, but you will never have 100% match. How you see colors on the monitor is effected by several factors:Ambient light, white point of the monitor, luminance of the monitor and color profile used by computer. You use color profile to factor out the variations of other factors. Most monitors will have its luminance set too high and at that setting monitor physically cannot display as many colors as your camera can capture or your printer can print. The luminance value which will give you widest color gamut on your particular monitor will be different than that of mine so I cannot tell you what value for luminance to use, however values between 60 and 120 are common. For best results your monitor luminance should be set to the value that gives highest color gamut AND you should be using different color profile for different lighting condition. For example: if during the day your room is lit by sun coming through your window, in the evening it is lit by combination of sunlight and table lamp and at night it is lit by main ceiling light; then you should have 3 color profiles for your monitor. Here is a write up how to change color profiles used by your computer under windows 7.

Copy/Paste from here:

http://answers.microsoft.com/en-us/windows/forum/windows_7-desktop/cant-apply-an-icc-profile-to-display-cant/71b8d8e8-afa3-435a-aae4-6a8a184b6439

  1. ASSOCIATE YOUR PROFILES WITH A DISPLAY AND SET AS DEFAULT
    To apply an existing ICC profile (an ICM file created by some calibration process), do the following -
    Control Panel / Display / Change Display Settings / Advanced Settings / Color Management / Color Management  / Devices / select one of your displays

/ click "use my settings for this device"

/ if necessary add the applicable profile to the "Profiles associated with this device" box using the "Add" button (if your profile is not already listed but is available somewhere on the network or computer) / click on the correct profile in that box and click "Set as Default Profile".

Usually profiles are stored here: “Windows>System 32>Spool>Drivers>Color”
*1 the CM dialog boxes don't label your displays the same way as other dialog boxes, they seem to lose the manufacturer and model number info that is available elsewhere, so your ABC model nn display comes up as Display: 1. Generic PnP monitor .  Also note that at least on my system, display '1' was in fact display '2' in other display settings dialog boxes, and vice versa. 
2. ENABLE CALIBRATION LOADING BY WINDOWS
Here's the hidden bit of help file...

To enable or disable calibration loading by Windows , you must be logged on with a user account that has administrative privileges.

  1. Click to open Color Management.
  2. Click the Advanced tab, and click Change system defaults .
  3. Click the Advanced tab in the Color Management - System Defaults dialog box, and do one of the following:
  • To enable Windows to load display calibrations,select the Use Windows display calibration check box.
  • To prevent Windows from loading display calibrations, clear the Use Windows display calibration check box.
  1. Click Close in the Color Management - System Defaults dialog box.
  2. 5.     Click Close in the Color Management dialog box.

If any one wants to add step by step instructions on how to do color correction in post using photograph of color checker, be my guest. Too many different software packages for me to type it all up...

Bob Collette
Veteran MemberPosts: 3,714Gear list
Like?
Re: Color managment - Please sticky if worthy
In reply to fft81, Mar 30, 2013

While your writeup is generally correct, there are some areas that don't agree with my understanding of color management.

Printer: Actually, the printer ICC profile does take into account the viewing illuminant.  By default, the viewing illuminant is assumed to be D50, however some profiling software allows you to change the viewing illuminant to a different standard.  However, you are correct in that the viewing illuminant will affect the print appearance.  For example, if you view a print under incandescent lighting, it will look different than if viewed under daylight.

When a printer is profiled, a set of color patches with known code values (RGB or CMYK) is printed with no color management applied (printer's native response).  The resulting print is measured using a spectrophotometer and the resulting colorimetric data is used to build a mathematical model of the printer.  Once the model is constructed (RGB/CMYK to Colorimetric), the inverse model can be calculated (Colorimetric to RGB/CMYK).  If we assume an RGB system, there are 16.7 million possible color values that can be requested.  Obviously, the printer ICC profile cannot have 16.7 million entries contained within it.  A 3-D lookup table is used with a number of entries ranging from tens of thousand to hundreds of thousands (depending upon the size & quality of the profile).  The other "missing" entries are interpolated from the 3-D table.

In a color managed system, the application software (e.g. Photoshop) reads the RGB code value for an image pixel and maps it through the image color space (sRGB, AdobeRGB, etc.) to get a colorimetric value (L*a*b*) for that pixel.  The colorimetric value is what is then sent to the printer.  The printer ICC profile takes the requested colorimetric value and then calculates the required printer code values (RGB or CMYK) to produce that color value (assuming it's within the printer's color gamut).

Monitor: The monitor luminance value is normally chosen to give a good match to the print, given it's viewing illumination, not to maximize the monitor's color gamut (although it likely does improve it's gamut).  The higher the print viewing illumination, the higher the monitor luminance should be to get a "brightness" match.  If you view your print under relatively dim light, you'll need a very low monitor luminance to give a reasonable print-monitor brightness match.  On the other hand, if you view the print under bright illumination (sunny day), you'll need to set the monitor to a much higher luminance level to match the print.

 Bob Collette's gear list:Bob Collette's gear list
Canon PowerShot G3 +4 more
Reply   Reply with quote   Complain
fft81
Contributing MemberPosts: 896
Like?
Re: Color managment - Please sticky if worthy
In reply to Bob Collette, Mar 30, 2013

Bob Collette wrote:

While your writeup is generally correct, there are some areas that don't agree with my understanding of color management.

Printer: Actually, the printer ICC profile does take into account the viewing illuminant.  By default, the viewing illuminant is assumed to be D50, however some profiling software allows you to change the viewing illuminant to a different standard.  However, you are correct in that the viewing illuminant will affect the print appearance.  For example, if you view a print under incandescent lighting, it will look different than if viewed under daylight.

When a printer is profiled, a set of color patches with known code values (RGB or CMYK) is printed with no color management applied (printer's native response).  The resulting print is measured using a spectrophotometer and the resulting colorimetric data is used to build a mathematical model of the printer.  Once the model is constructed (RGB/CMYK to Colorimetric), the inverse model can be calculated (Colorimetric to RGB/CMYK).  If we assume an RGB system, there are 16.7 million possible color values that can be requested.  Obviously, the printer ICC profile cannot have 16.7 million entries contained within it.  A 3-D lookup table is used with a number of entries ranging from tens of thousand to hundreds of thousands (depending upon the size & quality of the profile).  The other "missing" entries are interpolated from the 3-D table.

In a color managed system, the application software (e.g. Photoshop) reads the RGB code value for an image pixel and maps it through the image color space (sRGB, AdobeRGB, etc.) to get a colorimetric value (L*a*b*) for that pixel.  The colorimetric value is what is then sent to the printer.  The printer ICC profile takes the requested colorimetric value and then calculates the required printer code values (RGB or CMYK) to produce that color value (assuming it's within the printer's color gamut).

Monitor: The monitor luminance value is normally chosen to give a good match to the print, given it's viewing illumination, not to maximize the monitor's color gamut (although it likely does improve it's gamut).  The higher the print viewing illumination, the higher the monitor luminance should be to get a "brightness" match.  If you view your print under relatively dim light, you'll need a very low monitor luminance to give a reasonable print-monitor brightness match.  On the other hand, if you view the print under bright illumination (sunny day), you'll need to set the monitor to a much higher luminance level to match the print.

Everything you mention above is correct. I was trying to avoid writing a 3 tome encyclopedia and just give people functional understanding of what to do to establish color managed workflow and what parameters effect that flow. Lets be honest, most people reading this forum are not going to try to disassemble OEM driver or try to write their own RIP.

Reply   Reply with quote   Complain
Petruska
Veteran MemberPosts: 6,766
Like?
DPR already has a nice write-up...
In reply to fft81, Mar 30, 2013

fft81 wrote:

Everything you mention above is correct. I was trying to avoid writing a 3 tome encyclopedia and just give people functional understanding of what to do to establish color managed workflow and what parameters effect that flow. Lets be honest, most people reading this forum are not going to try to disassemble OEM driver or try to write their own RIP.

http://www.dpreview.com/articles/4231851787/print-workflow

As have countless others on this forum, including Jtoolman's recent Youtube videos and other linked Youtube videos.

The Epson Sales rep even did a fairly decent job in the video linked to in a recent post the last day or two.

You added to the CM beast!

I  personally think that color management is extremely simple and don't understand why so many view/make it as difficult.

BTW, there are no stickies on the DPR forums.

Bob P.

Reply   Reply with quote   Complain
Simon Garrett
Veteran MemberPosts: 4,067Gear list
Like?
Re: Color managment - Please sticky if worthy
In reply to fft81, Mar 30, 2013

Thanks for posting.

Added to what Bob said, few minor points:

  • Technically, a profile is not a correction table.  It is a measurement of the colour characteristics of an input or output device (or colour space).  Profiles do this by describing the mapping between the device colour space and a "profile connection space" (CIELAB or CIEXYZ).  It may be a table, or a parametric description. 
  • For printers it isn't always the driver that does colour management.  Generally the program writing to the printer can do the colour management instead of the driver, and I think this is probably the way most photographers choose. 
  • For monitors, it isn't calibration that corrects the colour (or does most of the correction), it's profiling.  For most monitors, you can calibrate the white point and tone response curve (that is, correct them by means of driver look-up tables) but the program gets the correct colours by means of the colour space information in the profile, which is obtained by profiling.  In general, both profiling and calibration are done at the same time, but they're not the same thing. 

The last point seems to cause a lot of confusion.  When you profile and calibrate a monitor (e.g. with a color munki), two things are done:

  • Calibration: This means creating adjustment tables to allow the driver to correct the white point (e.g. to 6500K or whatever) and the tone response curve (e.g. to a gamma of 2.2).  Once the tables are created, they're loaded into the driver each time the computer boots, and the driver applies them to all image data it sends to the monitor.  This means that all programs get the corrected white point and TRC, except some games and video players, which may bypass the driver and go straight to the hardware. 
  • Profiling: This means measuring the colour space of the monitor (after calibration) and putting that measurement into the profile.  Programs that do colour management (and only those programs) can correct the colour space of image data before sending it to the monitor, to match it to the monitor characteristics. 

Some newer and high-end monitors can have their colour space calibrated, as well.  You can't alter the dyes and phosphors in the screen, but the firmware in the monitor may be able to emulate a colour space, provided that it's narrower than the monitor's native colour space. So, for example, a wide-gamut monitor may be able to emulate the sRGB colour space.  Reviews I've read on tftcentral and prad.de suggest that in-built calibrations of monitor colour space aren't always as accurate as profiles obtained by a colormunki or whatever.

So far as I know, printers are only ever profiled, not calibrated, but I stand to be corrected on this.

-- hide signature --

Simon

 Simon Garrett's gear list:Simon Garrett's gear list
Nikon D800
Reply   Reply with quote   Complain
xrdbear
xrdbear MOD
Veteran MemberPosts: 3,686
Like?
Re: Color managment - Please sticky if worthy
In reply to Simon Garrett, Mar 30, 2013

Simon Garrett wrote:

<Big Snip>

So far as I know, printers are only ever profiled, not calibrated, but I stand to be corrected on this.

-- hide signature --

Simon

I think most Pro printers are individually calibrated by the manufacturer to meet a standard set for the model. Some prnters also have internal calibration hardware to return them regularly to factory standard.

Great post, thanks.

-- hide signature --

Brian
Fine Art Print sales of the Isle of Skye at:
http://www.eyeofskye.co.uk/

Reply   Reply with quote   Complain
Bob Collette
Veteran MemberPosts: 3,714Gear list
Like?
Re: Color managment - Please sticky if worthy
In reply to xrdbear, Mar 30, 2013

Brian, you are correct.  When I worked for Kodak, all of their professional thermal printers had internal calibration tables that were user "loadable".  Kodak supplied a calibration utility (software) that would let the user calibrate the printing system (printer + media) back to the factory aim.  The software supported both visual and instrumented (densitometer) calibration, with instrumented preferred.  The philosophy behind it was that it was cheaper for a user to calibrate the printer than to build a custom profile for the printer/media.  Once the printer was operating at "factory aim", the factory supplied ICC profile was valid.  While still somewhat true, spectrophotometers such as the ColorMunki have come way down in price, so that it now is practical for a professional user to build a custom profile for their printer.

Simon, I liked your explanation that a monitor profile consists of two parts: a calibration LUT that gets the monitor to the proper white point and gamma, and the actual "profile" that models how the device (monitor) handles color.  Most people don't understand how a monitor ICC profile works. Great explanation!

 Bob Collette's gear list:Bob Collette's gear list
Canon PowerShot G3 +4 more
Reply   Reply with quote   Complain
JJ Winkel
Senior MemberPosts: 1,387
Like?
Let's put it to a simpler way ....
In reply to xrdbear, Mar 30, 2013

xrdbear wrote:

Simon Garrett wrote:

So far as I know, printers are only ever profiled, not calibrated, but I stand to be corrected on this.

I think most Pro printers are individually calibrated by the manufacturer to meet a standard set for the model. Some prnters also have internal calibration hardware to return them regularly to factory standard.

Profiling is to adapt the output of a calibrated printer to the actual paper it is printing on

-- hide signature --

JJ.

Reply   Reply with quote   Complain
JJ Winkel
Senior MemberPosts: 1,387
Like?
Nice, but didn't you forgot one important element ....
In reply to fft81, Mar 30, 2013

That is your brain !

It adapts whatever your you look at to what IT thinks is the reference,  if it decides some patch of colour is white it will be white for you whatever the lighting condition is.

-- hide signature --

JJ.

Reply   Reply with quote   Complain
Simon Garrett
Veteran MemberPosts: 4,067Gear list
Like?
Re: Color managment - Please sticky if worthy
In reply to Bob Collette, Mar 30, 2013

Thanks both.  Interesting to know that about printer calibration!

-- hide signature --

Simon

 Simon Garrett's gear list:Simon Garrett's gear list
Nikon D800
Reply   Reply with quote   Complain
zambie
Regular MemberPosts: 455Gear list
Like?
Re: Color managment - Please sticky if worthy
In reply to Simon Garrett, Apr 9, 2013

wow ... eye opening thread...

thanks all for sharing all this info!

 zambie's gear list:zambie's gear list
Canon EF 85mm f/1.8 USM
Reply   Reply with quote   Complain
Hugowolf
Forum ProPosts: 11,411
Like?
Re: Color managment - Please sticky if worthy
In reply to Simon Garrett, Apr 9, 2013

Simon Garrett wrote:

So far as I know, printers are only ever profiled, not calibrated, but I stand to be corrected on this.

Actually, users of Canon wide format (24 inches and wider) printers talk about calibrating the printer as a separate process to profiling paper on the printer. I don't use Canon printers, so I don't know what this entails.

Unlike Epson printers, Canon wide format printers have user replaceable heads. Perhaps what they are talking about is head alighnment, but perhaps not.

Brian A

Reply   Reply with quote   Complain
jtoolman
Senior MemberPosts: 4,534
Like?
Re: Color managment - Please sticky if worthy
In reply to Hugowolf, Apr 9, 2013

Hugowolf wrote:

Simon Garrett wrote:

So far as I know, printers are only ever profiled, not calibrated, but I stand to be corrected on this.

Actually, users of Canon wide format (24 inches and wider) printers talk about calibrating the printer as a separate process to profiling paper on the printer. I don't use Canon printers, so I don't know what this entails.

Unlike Epson printers, Canon wide format printers have user replaceable heads. Perhaps what they are talking about is head alighnment, but perhaps not.

Brian A

Is I am not mistaken, I believe that refers to the ability of the IPG printers ability to actually save paper specific settings such as level of ink density, thickness, surface and just about anything that pertains to that paper. You can run an ink optimization print to determine the correct ink amount or intensity for a specific paper, and all other parameters.

What makes this special is that unlike Epson printers, you can then save those settings as a actual paper choice with the actual papers name.

Normally we have to choose the closest available EPSON paper choice, that matches as closely as possible the 3rd party you are using. This of course, has nothing to do with Paper ICC profiles, only paper type settings.

Some manufacturers of fine papers will make available a file or installer for their papers ink and physical properties, which can be loaded into the Canon IPG Printer's driver.

So as you begin to create or install then, you end up with say Canson - "BLANK" as a paper choice in the driver. By choosing that paper choice, you will automatically set your driver to the correct parameters for it.

Joe

Reply   Reply with quote   Complain
Hugowolf
Forum ProPosts: 11,411
Like?
Re: Color managment - Please sticky if worthy
In reply to jtoolman, Apr 9, 2013

jtoolman wrote:

Hugowolf wrote:

Simon Garrett wrote:

So far as I know, printers are only ever profiled, not calibrated, but I stand to be corrected on this.

Actually, users of Canon wide format (24 inches and wider) printers talk about calibrating the printer as a separate process to profiling paper on the printer. I don't use Canon printers, so I don't know what this entails.

Unlike Epson printers, Canon wide format printers have user replaceable heads. Perhaps what they are talking about is head alighnment, but perhaps not.

Brian A

Is I am not mistaken, I believe that refers to the ability of the IPG printers ability to actually save paper specific settings such as level of ink density, thickness, surface and just about anything that pertains to that paper. You can run an ink optimization print to determine the correct ink amount or intensity for a specific paper, and all other parameters.

What makes this special is that unlike Epson printers, you can then save those settings as a actual paper choice with the actual papers name.

Normally we have to choose the closest available EPSON paper choice, that matches as closely as possible the 3rd party you are using. This of course, has nothing to do with Paper ICC profiles, only paper type settings.

Some manufacturers of fine papers will make available a file or installer for their papers ink and physical properties, which can be loaded into the Canon IPG Printer's driver.

So as you begin to create or install then, you end up with say Canson - "BLANK" as a paper choice in the driver. By choosing that paper choice, you will automatically set your driver to the correct parameters for it.

It would be good to hear confirmation of that from wide format Canon users.

It is indeed a pity that there wasn’t more copying of such good practices from other manufactures. The same goes for cameras too, but perhaps patent and copyright infringement prevents it.

On the Epson side, it would be good at least to see what parameters are set with each Epson paper/media setting.

Brian A

Reply   Reply with quote   Complain
Keyboard shortcuts:
FForum MMy threads