Is BPC part of the ICC standard?

No — it originated as an Adobe extension described in a public Adobe paper and is now implemented almost everywhere, including LittleCMS. The ICC later documented the technique.

Does BPC affect highlights?

White maps to white either way; the correction is anchored at the black end and tapers to nothing at white.

Should BPC be on for soft proofing?

Match the proof to the conversion you intend to run. Proof with the same intent and BPC setting you will export with.

Editor › Learn › Black Point Compensation: What It Does and When to Turn It Off

What is black point compensation?

Black point compensation (BPC) is an option applied during colour conversion that maps the darkest black of the source space to the darkest black of the destination space, linearly rescaling the tone range between them. Without it, any source shadow darker than the destination's black is clipped to solid black and shadow detail disappears. Keep it on for relative colorimetric print conversions; it does nothing meaningful under perceptual, which already compresses the range.

The problem: blacks are not equal

A display black is far darker than any printed black — ink on paper reflects a few percent of the light hitting it. When an image is converted with plain relative colorimetric, every source tone darker than the destination's achievable black lands on the gamut boundary: solid black. A night photo with rich shadow gradations turns into a black hole with edges.

What BPC actually computes

BPC is an Adobe-designed extension, adopted broadly (including by LittleCMS), not part of the core ICC conversion itself. Conceptually it measures the source and destination black points in XYZ, then applies a linear scaling of the intermediate colour values so the source black lands exactly on the destination black and white stays at white. Every tone in between is proportionally lightened — shadow SEPARATION survives, at the price of absolute shadow tones rising slightly.

When to leave it on, when off

On: converting RGB photographs to CMYK with relative colorimetric — this is the standard production setup.
On: converting between CMYK conditions with noticeably different black points (coated vs uncoated).
Irrelevant: perceptual intent — its gamut compression already handles the black mismatch; most implementations quietly ignore BPC there.
Off: absolute colorimetric proofing, where the whole point is to reproduce the destination condition exactly, including its limited black.
Off: when you must verify the raw colorimetric behaviour of a profile, e.g. debugging a suspect profile.

Seeing it

Soft-proof a low-key image against an uncoated-paper profile with BPC toggled off, then on. Off: shadows merge into flat black. On: the same regions keep their gradation, slightly lifted. PhotoAIA exposes the BPC toggle in its proof and conversion settings, running the real LittleCMS pipeline locally, so this comparison takes seconds on your own file.

Try it in PhotoAIA

Open a low-key photograph — night scenes and dark product shots work well.
Enable the soft proof against an uncoated-paper CMYK profile (the smaller black makes the effect obvious).
In Color Settings, turn Black Point Compensation OFF and look at the deepest shadows: they merge into one flat black.
Turn BPC back ON: the same regions keep their separation, slightly lifted.
Flip the toggle a few times while watching one shadow area — that difference is exactly what this article describes.

Open the editor and follow along

Questions

Is BPC part of the ICC standard?: No — it originated as an Adobe extension described in a public Adobe paper and is now implemented almost everywhere, including LittleCMS. The ICC later documented the technique.
Does BPC affect highlights?: White maps to white either way; the correction is anchored at the black end and tapers to nothing at white.
Should BPC be on for soft proofing?: Match the proof to the conversion you intend to run. Proof with the same intent and BPC setting you will export with.

Open the editor