File: ICC_Probe.txt

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Probe Profile

Probe1 Profile v1.1, 11-11-04, Updated 2-22-08

The 'probe profile' (Probev1_ICCv2.icc) is syntactically a v2 ICC output
device ('prtr') profile, and can be used in a workflow wherever such a
profile is required. The color space of this profile is CMYK, and its
PCS is Lab.

Colors processed via this profile are deliberately distorted in a
systematic way, to enable visual determination of the rendering intent
used when rendering ("BToA" or PCS to device transforms) and when
proofing ("AToB" or device to PCS transforms). This is useful, in cases
when color-management-aware software does not document the behavior.

The rendering intent transforms (BToA tags) of the probe profile ignore
the a* and b* components of incoming PCS colors, and map the L*
components directly to monotone tints of process colorants. (L* = 0 is
rendered as maximum colorant coverage, and L* = 100 is rendered as
unmarked media.) The B2A0 tag (perceptual rendering intent transform)
renders the L* values as tints of pure cyan. The B2A1 tag (relative
colorimetric intent transform) renders them as tints of pure magenta,
and the B2A2 tag (saturation intent transform) renders them as tints of
pure yellow. As such, one can visually determine the rendering transform
used in a workflow by processing an image with the profile and observing
the dominant hue of the rendered result.

The proofing (AToB) transforms of the probe profile modify a different
perceptual dimension, i.e., lightness. These transforms are derived from
color measurements of an actual device. For the perceptual (A2B0) tag,
the output 1D LUTs are set such that the measured L* values are scaled
and offset into the range 70 to 100. For the relative colorimetric
(A2B1) tag, the L* values are scaled and offset into the range 30 to 70.
For the saturation (A2B2) tag, they are scaled to the range 0 to 30.

In a proofing scenario, the rendering transform of the device being
proofed (e.g., a press) is followed first by the proofing transform of
the same device, and then by the rendering transform of the proofing
device (e.g., a desktop printer). If the probe profile is substituted
for the press profile in this scenario, one can simultaneously determine
which AToB transform and which BToA transform are applied, according to
the following table:

Rendering transform	Proofing transform	Color code
B2A0			A2B0			light cyan
B2A0			A2B1			mid-tone cyan
B2A0			A2B2			dark cyan
B2A1			A2B0			light magenta
B2A1			A2B1			mid-tone magenta
B2A1			A2B2			dark magenta
B2A2			A2B0			light yellow
B2A2			A2B1			mid-tone yellow
B2A2			A2B2			dark yellow

See examples of the effect of these Probe Profile transforms:
<http://www.color.org/probeprofile_examples.xalter>

The media white point ('wtpt' tag) of the probe profile is set to
X =.75, Y = .5, and Z = .25 (a reddish color). This is an attempt to
provide additional visual discriminability between the relative and
absolute colorimetric intents of the proofing (AToB) transform.
Determination may be made by sending a 'white' image through the
workflow.

A v4 version of the probe profile is also posted as Probev1_ICCv4.icc.
Technically, this is non-compliant with the v4 ICC specification,
because (obviously) the media relative colorimetric intent tags are not
based on real measurement data, as is required for v4 profiles. However,
many CMMs and applications may not complain about this, and the v4 probe
may still be useful as a workflow analysis tool. Thanks to Uwe-Jens
Krabbenhoeft (Heidelberg) for converting the v2 probe to the v4 version.

Of course, these profiles are provided 'as is' and without warranty of
any kind.

Further details are available as "Exploiting Pseudocolor in ICC Workflow
Analysis," Abhay Sharma and John Dalrymple, Proc. IS&T 12th Color
Imaging Conference, Scottsdale, AZ, Nov 9-12, 2004.

Probev2_ICCv4 Profile with MPE support

The v2 Probe profile Probev2_ICCv4.icc is similar to Probev1_ICCv4.icc
with the addition of optional tags based on the MultiProcessingElement
tag type (See ICC Revision 02-11-2006: Floating Point Device Encoding
Range). This includes support for the new rendering intents BToD and
DToB, The behaviour of the v2 Probe profile is the same as the v1
profile with the following additions:

  * The B2D0 tag (MPE perceptual rendering intent transform) renders the
    L* values as tints of pure red (a combination of magenta plus
    yellow). The B2D1 tag (MPE relative colorimetric intent transform)
    renders them as tints of pure green (a combination of cyan and
    yellow), and the B2D2 tag (MPE saturation intent transform) renders
    them as tints of pure blue (a combination of cyan and magenta).
  * With the MPE perceptual (D2B0) tag, the luminance output is inverted
    and set such that the measured L* values are scaled and offset into
    the range 70 to 100. The MPE relative colorimetric (DToB1) and
    saturation (DToB2) tags invert the output so that the measured L*
    values are scaled and offset into the range 33-66 and 0-33
    respectively.

The following table makes it possible to determine which DToB transform
and/or which DToA transform was applied.

Rendering transform	Proofing transform	Color code
B2A0			D2B0			inverted light cyan
B2A0			D2B1			inverted mid-tone cyan
B2A0			D2B2			inverted dark cyan
B2A1			D2B0			light magenta
B2A1			D2B1			mid-tone magenta
B2A1			D2B2			dark magenta
D2A0			A2B0			light red
D2A0			A2B1			mid-tone red
D2A0			A2B2			dark red
D2A0			D2B0			inverted light red
D2A0			D2B1			inverted mid-tone red
D2A0			D2B2			inverted dark red
D2A1			A2B0			light green
D2A1			A2B1			mid-tone green
D2A1			A2B2			dark green
D2A1			D2B0			inverted light green
D2A1			D2B1			inverted mid-tone green
D2A1			D2B2			inverted dark green
D2A2			A2B0			light blue
D2A2			A2B1			mid-tone blue
D2A2			A2B2			dark blue

source: <http://www.color.org/probeprofile.xalter>