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I don't understand clipping in Lightroom.

From my understanding, shadow clipping is displayed as a white triangle on the left of the histogram and as blue zones on the photo. Similarly, highlight clipping is displayed as a white triangle on the right of the histogram ans as red zones on the photo.

However, on some photos, Lightroom displays blue and red zones, but the white triangles are not shown in the diagram. Here's an example of a fragment of a photo which clearly displays a relatively large zone in red, and a tiny zone in blue (the top of the antenna):

enter image description here

For the same photo, the histogram is shown like that:

enter image description here

Notes:

  • View > Show clipping is checked. If I reduce the blacks or raise the whites, then the triangles appear.

  • When I hover over the red zone, some but not all points are displayed R 100 G 100 B 100 % below the histogram.

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The color of the triangles indicates which channels are clipped: white triangle -- all channels. Red channel clipped? Red triangle. Blue and green channels clipped: cyan triangle. And so on...

The luminosity of the triangles is related to the %age of pixels that Lightroom considers clipped. Few pixels relative to image area? Dark triangles. Many pixels? Bright triangles. That's why if you boost highlights you'll see the white triangle -- more pixels clipped in all channels in your image.

This also answers your second question: any channel that is clipped will trigger the warning, not just white (RGB 100 100 100).

  • The luminosity of the triangles is related to the %age of pixels that Lightroom considers clipped: not exactly; at least, it's not what I see when I use Lightroom. There seem to be two states: white triangle, and dark gray triangle, and nothing in between. This is why I supposed that a white one means there is at least one pixel on the image which is (100, 100, 100) or (0, 0, 0). Another possibility is that Lightroom has a specific threshold, such as 2% of all pixels, or anything else. But in this case, I'm wondering what is the threshold, and why does it exist? – Arseni Mourzenko Mar 29 at 19:16
  • I didn't say it was a linear relationship. Just bright and dark triangles. I don't know the percentage -- why does it matter? And if you liked the answer, upvote :-) – the_limey Mar 30 at 14:36
  • Indeed, you didn't say that. I misread your answer; sorry about that. I still don't understand the reasoning behind the threshold. The goal of the white triangles is to alert the user that the photo is unsuited for printing (or even being displayed on some monitors). But how Lightroom decides what percentage is acceptable or not, without even knowing how the photo will be printed/displayed later? Also, the threshold may depend on how close white or black pixels are to each other, i.e. if they form a continuous zone. In my example, they do (although it's only a tiny part of the whole photo). – Arseni Mourzenko Mar 30 at 19:55
  • "But in this case, I'm wondering what is the threshold, and why does it exist?" Things like street lights and the sun in a sunset photo will be clipped quite a bit of the time. If this is a small amount of the photo it will be red, whereas if there's a lot of this it will be white. – Mike Dixon Aug 26 at 14:29

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