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:
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.
The following naming states that the Probe Profile is at version 1, while the ICC specification may be v2 or v4. The profiles are provided as compressed .sit or .zip files.
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:
|B2A0||D2B0||inverted light cyan|
|B2A0||D2B1||inverted mid-tone cyan|
|B2A0||D2B2||inverted dark cyan|
|D2A0||D2B0||inverted light red|
|D2A0||D2B1||inverted mid-tone red|
|D2A0||D2B2||inverted dark red|
|D2A1||D2B0||inverted light green|
|D2A1||D2B1||inverted mid-tone green|
|D2A1||D2B2||inverted dark green|