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Extract ICC Profile from Images

Color management is regarded as a black art my many application and system developers but it is becoming an increasingly important subject as color fidelity between devices is now a requirement for many applications.

What is color? Color (or colour) is the visual perceptual property corresponding in humans to the categories called red, green, blue, and others. Color derives from the spectrum of light (distribution of light power versus wavelength) interacting in the eye with the spectral sensitivities of the light receptors. Color categories and physical specifications of color are also associated with objects, materials, light sources, etc., based on their physical properties such as light absorption, reflection, or emission spectra. Color spaces, such as RGB, CYMK and CIE 1931, represent colors as tuples of numbers. Other types of color spaces such as RAL are color matching schemes used by designers, interior decorators et al.

The ICC (International Color Consortium) Profile Format is an industry initiative to provide an interchange format to help solve the problems of specifying color, and in transferring color graphics from, and between systems and devices. The current version (ICC.1:2010 Profile Version 4.3.0.0, technically identical to ISO 15076-1:2010) of the specification enables color matching of images from the point of creation to the final output, whether display or print, in applications or within an operating system. Annex B, which is informative only, provides guidelines for embedding a profile in EPS (Encapsulated PostScript) or an image file. For example, in JPEG image files, the APP2 marker is used to introduce the ICC profile tag which, in turn, is identified by beginning the data with a special null terminated byte sequence, “ICC_PROFILE”.

As shown below, the ICC profile structure within an image is defined as a header followed by a tag table followed by a series of tagged elements (all defined in the specification) that can be accessed randomly and individually.

Within the profile structure:

  • All profile data is encoded as big-endian.
  • The first set of tagged element data immediately follows the tag table.
  • Tagged element data is aligned on a 4-byte boundary using NULLs.

The profile header is intended to provide the necessary information to allow a receiving system to properly search and sort ICC profiles. It is 128 bytes in length and contains 18 fields. Here is a detailed breakdown:

Note that the signature field always contains the value “acsp” (61637379h). I use that fact later to locate an ICC profile in an image.

The tag table provides a table of contents for the tagging information in each individual profile. The collection of tagged elements consist of three types: required data, optional data and private data.

Each individual tag element includes a tag signature, the beginning address offset and size of the data. Signatures are defined as a 4-byte hexadecimal number as shown above. This design allows applications to read the element tag table and then load into memory only the information necessary to their particular application. A detailed descriptions of the tags, along with their intent, are included in the ICC specification.

Here is a simple C utility (iccdump) which demonstrates one way of of extracting an ICC profile from an image, if one exists, and displaying it in a human-readable format.

/*
 * Copyright (c) 2012  Finnbarr P. Murphy.   All rights reserved
 *
 */

/* 
 * Copyright 1997 - 2012 Graeme W. Gill
 *
 * This material is licensed with an "MIT" free use license:-
 */


#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <fcntl.h>
#include <string.h>
#include "icc.h"

#define MXTGNMS 30

void
error(char *fmt, ...)
{
    va_list args;

    fprintf(stderr,"ERROR: ");
    va_start(args, fmt);
    vfprintf(stderr, fmt, args);
    va_end(args);
    fprintf(stderr, "\n");

    exit(1);
}


void 
usage(void) {
    fprintf(stderr,"usage: iccdump infile\n");
    exit(1);
}


int
main(int argc, char *argv[]) {
    int offset = 0;        /* Offset to read profile from */
    int found;
    icmFile *fp, *op;
    icc *icco;
    int rv = 0;
    
    if (argc < 2)
        usage();

    /* Open up the file for reading */
    if ((fp = new_icmFileStd_name(argv[1],"r")) == NULL)
        error("Cannot open file '%s'", argv[1]);

    if ((icco = new_icc()) == NULL)
        error("Creation of ICC object failed");

    /* open output stream */
    if ((op = new_icmFileStd_fp(stdout)) == NULL)
        error("Cannot open stdout stream");

    do {
        found = 0;

        /* Dumb search for magic number */
        int fc = 0;
        char c;
        
        if (fp->seek(fp, offset) != 0)
            break;

        while(found == 0) {
            if (fp->read(fp, &c, 1, 1) != 1)
                break;
            
            offset++;
                
            switch (fc) {
                case 0:
                    if (c == 'a')
                        fc++;
                    else
                        fc = 0;
                    break;
                case 1:
                    if (c == 'c')
                        fc++;
                    else
                        fc = 0;
                    break;
                case 2:
                    if (c == 's')
                        fc++;
                    else
                        fc = 0;
                    break;
                case 3:
                    if (c == 'p') {
                        found = 1;
                        offset -= 40;
                    } else
                        fc = 0;
                    break;
            }
        }

        if (found) {
            printf("Embedded ICC profile found at file offset %d (0x%x)\n",offset,offset);
            if ((rv = icco->read(icco,fp,offset)) != 0)
                error("%d, %s", rv, icco->err);
            else 
                icco->dump(icco, op, 3);
            offset += 128;
        }
    } while (found != 0);

    icco->del(icco);
    op->del(op);
    fp->del(fp);

    return 0;
}


This utility uses the excellent ICC profile parsing code developed by Graeme Gill as part of the Argyll CMS (Color Management System).

Here is sample output:

$ ./iccdump sample1.jpg
Embedded ICC profile found at file offset 6905 (0x1af9)
icc:
Header:
  size         = 3144 bytes
  CMM          = 'Lino'
  Version      = 2.1.0
  Device Class = Display
  Color Space  = RGB
  Conn. Space  = XYZ
  Date, Time   = 9 Feb 1998, 6:49:00
  Platform     = Microsoft
  Flags        = Not Embedded Profile, Use anywhere
  Dev. Mnfctr. = 'IEC '
  Dev. Model   = 'sRGB'
  Dev. Attrbts = Reflective, Glossy, Positive, Color
  Rndrng Intnt = Perceptual
  Illuminant   = 0.964203, 1.000000, 0.824905    [Lab 100.000000, 0.000498, -0.000436]
  Creator      = 'HP  '

tag 0:
  sig      'cprt'
  type     'text'
  offset   336
  size     51
Text:
  No. chars = 43
    0x0000: Copyright (c) 1998 Hewlett-Packard Company

tag 1:
  sig      'desc'
  type     'desc'
  offset   388
  size     108
TextDescription:
  ASCII data, length 18 chars:
    0x0000: sRGB IEC61966-2.1
  No Unicode data
  ScriptCode Data, Code 0x0, length 18 chars
    0x0000: 73 52 47 42 20 49 45 43 36 31 39 36 36 2d 32 2e 31 00 

tag 2:
  sig      'wtpt'
  type     'XYZ '
  offset   496
  size     20
XYZArray:
  No. elements = 1
    0:  0.950455, 1.000000, 1.089050    [Lab 100.000000, -2.387320, -19.404505]

tag 3:
  sig      'bkpt'
  type     'XYZ '
  offset   516
  size     20
XYZArray:
  No. elements = 1
    0:  0.000000, 0.000000, 0.000000    [Lab 0.000000, 0.000000, 0.000000]

tag 4:
  sig      'rXYZ'
  type     'XYZ '
  offset   536
  size     20
XYZArray:
  No. elements = 1
    0:  0.436066, 0.222488, 0.013916    [Lab 54.290039, 80.819767, 69.895569]

tag 5:
  sig      'gXYZ'
  type     'XYZ '
  offset   556
  size     20
XYZArray:
  No. elements = 1
    0:  0.385147, 0.716873, 0.097076    [Lab 87.817866, -79.257408, 80.986979]

tag 6:
  sig      'bXYZ'
  type     'XYZ '
  offset   576
  size     20
XYZArray:
  No. elements = 1
    0:  0.143066, 0.060608, 0.714096    [Lab 29.565320, 68.301563, -112.050315]

tag 7:
  sig      'dmnd'
  type     'desc'
  offset   596
  size     112
TextDescription:
  ASCII data, length 22 chars:
    0x0000: IEC http://www.iec.ch
  No Unicode data
  ScriptCode Data, Code 0x0, length 22 chars
    0x0000: 49 45 43 20 68 74 74 70 3a 2f 2f 77 77 77 2e 69 65 63 2e 63 68 00 

tag 8:
  sig      'dmdd'
  type     'desc'
  offset   708
  size     136
TextDescription:
  ASCII data, length 46 chars:
    0x0000: IEC 61966-2.1 Default RGB colour space - sRGB
  No Unicode data
  ScriptCode Data, Code 0x0, length 46 chars
    0x0000: 49 45 43 20 36 31 39 36 36 2d 32 2e 31 20 44 65 66 61 75 6c 74 20 
    0x0016: 52 47 42 20 63 6f 6c 6f 75 72 20 73 70 61 63 65 20 2d 20 73 52 47 
    0x002c: 42 00 

tag 9:
  sig      'vued'
  type     'desc'
  offset   844
  size     134
TextDescription:
  ASCII data, length 44 chars:
    0x0000: Reference Viewing Condition in IEC61966-2.1
  No Unicode data
  ScriptCode Data, Code 0x0, length 44 chars
    0x0000: 52 65 66 65 72 65 6e 63 65 20 56 69 65 77 69 6e 67 20 43 6f 6e 64 
    0x0016: 69 74 69 6f 6e 20 69 6e 20 49 45 43 36 31 39 36 36 2d 32 2e 31 00 

tag 10:
  sig      'view'
  type     'view'
  offset   980
  size     36
Viewing Conditions:
  XYZ value of illuminant in cd/m^2 = 19.644501, 20.371796, 16.808899
  XYZ value of surround in cd/m^2   = 3.928894, 4.074387, 3.361786
  Illuminant type = D50

tag 11:
  sig      'lumi'
  type     'XYZ '
  offset   1016
  size     20
XYZArray:
  No. elements = 1
    0:  76.036469, 80.000000, 87.124619    [Lab 483.828848, -10.285791, -83.613628]

tag 12:
  sig      'meas'
  type     'meas'
  offset   1036
  size     36
Measurement:
  Standard Observer = 1931 Two Degrees
  XYZ for Measurement Backing = 0.000000, 0.000000, 0.000000    [Lab 0.000000, 0.000000, 0.000000]
  Measurement Geometry = Unknown
  Measurement Flare =   1.0%
  Standard Illuminant = D65

tag 13:
  sig      'tech'
  type     'sig '
  offset   1072
  size     12
Signature
  Technology = Cathode Ray Tube Display

tag 14:
  sig      'rTRC'
  type     'curv'
  offset   1084
  size     2060
Curve:
  No. elements = 1024
      0:  0.000000
      1:  0.000076
      2:  0.000153
      3:  0.000229
      4:  0.000305
      5:  0.000381
      6:  0.000458

    .....

    1020:  0.993347
    1021:  0.995560
    1022:  0.997772
    1023:  1.000000

tag 15:
  sig      'gTRC'
  type     'curv'
  offset   1084
  size     2060
Curve:
  No. elements = 1024
      0:  0.000000
      1:  0.000076
      2:  0.000153
      3:  0.000229
      4:  0.000305
      5:  0.000381
      6:  0.000458
 
     ......

    1020:  0.993347
    1021:  0.995560
    1022:  0.997772
    1023:  1.000000

tag 16:
  sig      'bTRC'
  type     'curv'
  offset   1084
  size     2060
Curve:
  No. elements = 1024
      0:  0.000000
      1:  0.000076
      2:  0.000153
      3:  0.000229
      4:  0.000305
      5:  0.000381
      6:  0.000458

    ..... 

    1020:  0.993347
    1021:  0.995560
    1022:  0.997772
    1023:  1.000000


And here is an example of a simpler profile:

$ ./iccdump sample2.jpg

Embedded ICC profile found at file offset 9279 (0x243f)
icc:
Header:
  size         = 560 bytes
  CMM          = 'ADBE'
  Version      = 2.1.0
  Device Class = Display
  Color Space  = RGB
  Conn. Space  = XYZ
  Date, Time   = 3 Jun 1999, 0:00:00
  Platform     = Macintosh
  Flags        = Not Embedded Profile, Use anywhere
  Dev. Mnfctr. = 'none'
  Dev. Model   = 0x0
  Dev. Attrbts = Reflective, Glossy, Positive, Color
  Rndrng Intnt = Perceptual
  Illuminant   = 0.964203, 1.000000, 0.824905    [Lab 100.000000, 0.000498, -0.000436]
  Creator      = 'ADBE'

tag 0:
  sig      'cprt'
  type     'text'
  offset   252
  size     50
Text:
  No. chars = 42
    0x0000: Copyright 1999 Adobe Systems Incorporated

tag 1:
  sig      'desc'
  type     'desc'
  offset   304
  size     107
TextDescription:
  ASCII data, length 17 chars:
    0x0000: Adobe RGB (1998)
  No Unicode data
  No ScriptCode data

tag 2:
  sig      'wtpt'
  type     'XYZ '
  offset   412
  size     20
XYZArray:
  No. elements = 1
    0:  0.950455, 1.000000, 1.089050    [Lab 100.000000, -2.387320, -19.404505]

tag 3:
  sig      'bkpt'
  type     'XYZ '
  offset   432
  size     20
XYZArray:
  No. elements = 1
    0:  0.000000, 0.000000, 0.000000    [Lab 0.000000, 0.000000, 0.000000]

tag 4:
  sig      'rTRC'
  type     'curv'
  offset   452
  size     14
Curve:
  Curve is gamma of 2.199219

tag 5:
  sig      'gTRC'
  type     'curv'
  offset   468
  size     14
Curve:
  Curve is gamma of 2.199219

tag 6:
  sig      'bTRC'
  type     'curv'
  offset   484
  size     14
Curve:
  Curve is gamma of 2.199219

tag 7:
  sig      'rXYZ'
  type     'XYZ '
  offset   500
  size     20
XYZArray:
  No. elements = 1
    0:  0.609741, 0.311111, 0.019470    [Lab 62.601347, 90.371212, 78.149349]

tag 8:
  sig      'gXYZ'
  type     'XYZ '
  offset   520
  size     20
XYZArray:
  No. elements = 1
    0:  0.205276, 0.625671, 0.060867    [Lab 83.214105, -129.089932, 87.172524]

tag 9:
  sig      'bXYZ'
  type     'XYZ '
  offset   540
  size     20
XYZArray:
  No. elements = 1
    0:  0.149185, 0.063217, 0.744568    [Lab 30.210038, 69.243738, -113.612302]


The entire source code and a Makefile is available under the iccdump directory the Various repository on GitHub.

Enjoy!

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