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IccProfile

PsychtoolboxPsychCal

icc=IccProfile(command,file,icc)



UNIMPLEMENTED! This function is not yet available in Psychtoolbox-3.
Porting it from the old Psychtoolbox-2 should be doable for somebody
with basic C programming skills. If you feel like contributing this
function, please do so!



IccProfile.mex will read any ICC or ColorSync profile. The
International Color Consortium (ICC) published a standard file
format for saving color calibration data for imaging devices. This
includes digital cameras, scanners, printers, and monitors. Users
of the Psychophysics Toolbox will be primarily interested in the
use of an ICC Profile to characterize their CRT monitor or LCD
display. The idea is that the file contains all the necessary
information to transform the specification of a color in a standard
perceptual space (e.g. CIE X,Y,Z) into the numbers necessary to
display that color.
web http://www.color.org/profiles.html ;

USAGE:


icc=IccProfile('Read',file) % Gets data into Matlab.
folder=IccProfile('Folder') % ColorSync Profiles folder
file=IccProfile('Filename',screenNumber,newfile) % Get/set screen's profile.
IccProfile('ShortDump',file,[tag]) % For exploring.
IccProfile('Dump',file,[tag]) % IccProfile('LongDump',file,[tag]) %

"file" is a filename, a partial or complete path, for an ICC
Profile file. The default folder is the ColorSync Profiles
folder (in the System Folder).
"icc" is a Matlab struct.
"folder" path string gives location of ColorSync Profiles folder.
"tag" is a four-character string identifying a chunk of
information in the icc profile, e.g. 'rTRC' for the red
Tone Reproduction Curve (i.e. gamma curve for red phosphor)
or 'gXYZ' for the the X,Y,Z color coordinates of the green
phosphor.
'Read' returns a Matlab struct with one field for each tag in the
profile. The field will still be present, but empty, if the
tag is of an unknown type, or if an error was encountered in
reading the tag. (Use 'Dump' to diagnose.) 'Read' recognizes
most of the tag types relevant to monitor calibration.
'Folder' returns the path (a string) for the ColorSync Profiles folder.
Use DIR(IccProfile('Folder')) to get a list of files there.
'Filename' get and/or set the filename of the profile associated with your
screen. Or use the Monitors control panel (go to color) to choose.
Note that setting the file has the side effect of loading
the video card's gamma table from the 'vcgt', if present in
your profile.
'Dump' describes every tag in the profile. Or just one tag.
'ShortDump' describes every tag in the profile, with less detail.
'LongDump' describes every tag in the profile, with more detail.

EXAMPLE:


file=iccprofile('filename',0)
icc=iccprofile('read',file)

This will read all the information in the profile associated with
screen 0 (the main screen) and provide it to you as a handy Matlab struct
"icc" that you can use in your software. For explanation of the contents,
consult the official ICC documentation, plus Apple's documentation of
their custom tags: 'vcgt' and 'mmod'.
web http://www.color.org/profiles.html ;
web http://developer.apple.com/techpubs/macos8/MultimediaGraphics/ColorSyncManager/ManagingColorWithColorSync/ColorSync.7b.html

EXPLANATION OF TAG TYPE:


Most of the information in a profile is stored as chunks of data,
called elements. Each element has a unique 4-character tag name and
a 4-character tag type. IccProfile accepts every tag name, and
installs a corresponding field in your icc struct, with the same
name (e.g. 'desc'). However, IccProfile will be able to transfer the
content of the profile element to your struct only if IccProfile
recognizes the type. At present, IccProfile can read the following
tag types:

NAME TYPE TAGS THAT USE IT.
Profile description 'desc' 'desc'
Tone reproduction curve 'curv' 'rTRC','gTRC','bTRC','kTRC'
X,Y,Z of a color 'XYZ ' 'rXYZ','gXYX','bXYZ','wtpt','bkpt','lumi'
Text string 'text' 'cprt'
Date and time 'dtim' 'calt'
Viewing conditions 'view' 'view'
Measurement type 'meas' 'meas'
Data (unformatted) 'data'
Unsigned 8-bit int array 'ui08'
Unsigned 16-bit int array 'ui16'
Unsigned 32-bit int array 'ui32'
Unsigned 64-bit int array 'ui64'
Unsigned 32-bit fixed array 'uf32'
Signed 32-bit fixed array 'sf32'
Video card gamma 'vcgt' 'vcgt'
Make and model 'mmod' 'mmod'

TAG

'desc' profile description, a human readable text string
'rTRC' red tone reproduction curve
'gTRC' green tone reproduction curve
'bTRC' blue tone reproduction curve
'kTRC' gray tone reproduction curve
'rXYZ' red phosphor color
'gXYZ' green phosphor color
'bXYZ' blue phosphor color
'wtpt' white point
'bkpt' black point
'lumi' luminance in cd/m^2
'cprt' copyright
'calt' calibration date and time
'view' viewing conditions
'meas' measurement type
'vcgt' custom Apple tag for video card gamma table
'mmod' custom Apple tag for make and model of the device

NOTE: IccProfile may report errors in an apparently good profile.
This is because icclib enforces the ICC standard more strictly than
ColorSync does, so it picks up errors that were previously missed.
(On 7/31/00 we reported to Apple two such errors, affecting most of their
ColorSync Profiles, and added a work-around to IccProfile.)
You can try running Apple's "Profile First Aid", which detects and
fixs some common profile errors, though it too is less strict than
icclib. "Profile First Aid" 3.0.1 is installed in the Apple
Extras:ColorSync Extras folder when you install ColorSync 3.0.1
web http://asu.info.apple.com/swupdates.nsf/artnum/n11674 ;

CALIBRATION:


You can buy a calibration package consisting of a program (e.g.
ColorBlind ProveIt! or Monaco EZColor) and a simple colorimeter to
easily create an ICC profile for your monitor. Using IccProfile.mex,
it should be easy to use that calibration data to do your color
corrections, but we haven't actually tried that yet. Here are a few
calibrators that seems to be good, from what we've read. We've
included links to the manufacturer (if available) and to Jon Cone's
inkjetmall web site because he knows a lot about digital
printing and has good advice about choosing among these products.

ColorBlind ProveIt! software $50
Does not include colorimeter. Can be used alone, using perceptual
matching, or with the Sequel Chroma 4 colorimeter, below.
web http://www.color.com/Products/proveit.html ;
web http://www.inkjetmall.com/store/prove-it.html ;

Sequel Chroma 4 CRT & LCD monitor colorimeter $249
Requires software, which is not included. Compatible with ColorBlind
and Monaco.
web http://www.inkjetmall.com/store/measuring-devices.html#monitors ;

Monaco EZColor software $299
MonacoSENSOR colorimeter $249 (or both together for $499)
web http://www.monacosys.com/monacoezcolor.html ;

The ColorBlind+Sequel package, for $299, is cheaper than the $499
Monaco package, and the ColorBlind software seems to be at least as
highly regarded as Monaco's by Jon Cone and others using it to
calibrate their monitors for critical digital color printing.

Denis Pelli

ACKNOWLEDGEMENT: IccProfile.mex is largely a Matlab interface to
the excellent free icclib created in C by Graeme Gill, for which we
are very grateful.
web http://web.access.net.au/argyll/color.html ;




Path   Retrieve current version from GitHub | View changelog
Psychtoolbox/PsychCal/IccProfile.m


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