Does anyone know why I am seeing these red pixels in the LR develop section? When exported to jpeg the red pixels are not there! This has only happened recently. I have checked my display drivers and recalibrated my screen but can't seem to stop it appearing. It has appeared in lots of photos recently. Not aware of any changes other than LR updates.
This is a visual aid that indicates clipped highlights. Clipped shadows will be blue.
You have probably pressed J to make it appear. Press J again to hide it.
Or drag the highlights slider to the left to recover the clipped highlights, and the red will go away.
(you'll get the same effect, in black & white, by holding down Alt while dragging the slider.
To add to Per's advice, see the little white triangle at top right of the screenshot, in the top corner of the histogram? It's white to show that you've activated the highlight clipping warning.
Clicking on it will also turn it off/on.
Thanks Per & Keith,
It was the triangle in the histogram!