Black point compensation (BPC) helps maintain shadow detail when converting between source and destination color spaces. The black point of the source space is mapped to that of the destination space, and if not enabled, any colors that are darker than the destination space are clipped and details in those darkest black areas are lost, which is sometimes referred to as "crushed-" or "blocked-up-" shadows.
Although BPC algorithms differ between color engines, a simple linear transform on individual XYZ values is common. As a consequence, this method results in a shift of hue, saturation, or lightness, and leads to inaccurate color values. Therefore, Capture One does not support color black point compensated Lab readouts and it may be necessary to configure third-party applications to match (i.e., disable BPC) when validating values. The issue can be avoided by using output profiles that can represent black, where known, and is highly recommended unless the image is being processed to a device such as a printer.
Note that Perceptual rendering intent, when selected in Adobe Photoshop, always maps the darkest black of the source space to the destination space. Therefore, when validating readouts with values in Photoshop, it is recommended that Relative Colorimetric intent is adopted, with BPC disabled and Use Dither. This improves the gradations in shadow tones in 8-bit images during conversion. As BPC is a highly destructive process, it should be limited to the last operation in a color-managed workflow, where possible.
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