Selecting an appropriate Lab implementation

Color target reference values can be specified in a standard RGB color space but are more usually specified in the Lab (i.e., CIE 1976 (L*, a*, b*) or CIELAB) color space. In Capture One, Lab color values are based on a conversion of the selected output RGB color space profile in the ICC Profile field of the Process Recipe or the RGB profile selected using the Proof Profile option. Please ensure that the appropriate color space profile is selected.

Note that RGB profiles are open to interpretation, even those specified to ICC standards. Therefore, when comparing Lab values in Capture One with the RGB output file in third-party applications such as Adobe Photoshop or specific image analysis software, including Picturae Delt.ae, CMS (by Marti Maria) or ISA GoldenThread, several implementations for Lab values are supported.

1. In the main menu, select View -> Lab Readout and choose one of the following options.
   
   
   • Off. Select this option to return to displaying RGB/CMYK values (depending on the output profile selected).
   • Generic (D50). This is Lab conversion using D50 as the white point. This option is compatible with the majority of third-party software, including Delta.ae (by Picturae) and LCMS (by Marti Maria).
   • Generic (media white). It ensures Lab conversion with the media white (i.e., native white point of the color space) specified in the profile. To match colors and avoid chromatic adaptation (either as perceived colors when viewed or as the difference in conversion between D50 and D65) when a monitor is calibrated for sRGB or AdobeRGB (1998), the surface color of the test patch must be measured with respect to the D65 white point.
   • Adobe (generic). Lab conversion values are compatible with the Adobe Color Engine (ACE). Select this for the best match with Adobe Photoshop for most color profiles. Adobe applies slope-limiting on pure-gamma profiles such as Adobe RGB (1998) and ProPhoto RGB (ROMM). Therefore, in Adobe Photoshop, please select Relative Colorimetric intent, disable Black-Point Compensation (BPC), and enable Use Dither.
   • Adobe (neutral). Lab conversion values are compatible with the Adobe Color Engine (ACE) for sRGB. Select this option for the most accurate match using ACE with an sRGB profile. Although similar to the generic option, the Phase One Color Engine defines the white point (255, 255, 255) as neutral, thereby allowing ACE to recognize the sRGB profile as a faithful interpretation.
   • GoldenThread (ICC). Lab conversion values are compatible with GoldenThread software by Image Science Associates (ISA). Select this option for compatibility with the app’s image analysis based on an ICC profile.
   • GoldenThread (standard). Lab conversion values are compatible with GoldenThread software by Image Science Associates. Select this option for compatibility with analysis based on standard color space. Note that the output profile in Capture One (selected in the Process Recipe) must match the option used in the analysis.
     
     
2. When one of the above options is selected, the cursor in use displays the values from a single location in the image in the Viewer’s toolbar.

3. When you want to permanently display the color values at more than one location, select the Add Color Readout cursor from the cursor toolbar and click on the image to anchor the readout.
   
   

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