The process of conversion from RGB to the Lab color space is determined by the profile in use. However, when using different color engines, there is some discrepancy in the way the data is translated.
When measuring colors (e.g., from patches in color chart) using readouts, the intention is to match the colors in the processed output file to the chart’s reference data. The camera profile describes how the colors of the captured image are to be transformed into a reference color space known as a Profile Connection Space (PCS), while the output profile describes how the colors from that are to be transformed in the output image file.
In Capture One, it is only necessary to process and output an image when using the file in third-party analysis software, otherwise, it is enough to measure the colors using the output profile as Capture One converts the results in the Viewer. The output profile determines the destination color space, which is set by the selected Process Recipe. The Proof Profile option may be used instead, however, note that, if an output file is required for analysis, the selected Process Recipe must use the same profile. Most modern applications, not to mention the chart maker’s reference data, specify colors as Lab color space coordinates or values, therefore, Capture One Pro can now display Lab values as an option.
While Lab is a reference color space adopted by the ICC in the PCS, there is variation in the way that third-party color engines convert the data in RGB profiles to the Lab color space. That is assuming an output file is required in RGB color space and is to be interpreted using an ICC output profile. Note that some third-party software analyzes colors directly without interpreting an ICC profile.