The histogram shown in ACR v 13 has the usual clipping warning indicators in the upper corners...but they don't work. Is there some setting somewhere to turn them on?
Have you clicked on the indicators so that they are highlighted? On my Windows 10 computer, if I do that then they work.
So you don't see the clipping at all, on images you know it should show?
First, try disabling GPU in the preferences (Preformance tab). Any better?
If not, recalibrate and build a new ICC display profile, the old one might be corrupted.
If you are using software/hardware for this task, be sure the software is set to build a matrix not LUT profile, Version 2 not Version 4 profile.
If turning OFF GPU works, it's a GPU bug and you need to contact the manufacturer or find out if there's an updated driver for it.
The clipping warnings show what colors are off the ends of the histogram, which is also usually indicated by a spike of those colors at the very ends, athough the clipping indicators may come on before enough colors pile-up to show a spike.
Along the lines of what TheDigitalDog is asking about:
Try sRGB or AdobeRGB or ProPhotoRGB and see if the clipping indicators show with these colorspaces.
Also, can you explain what isn't working about the clipping indicators?
You also asked how to turn clipping on and off besides clicking. If you hover over the indicators on the histogram it tells you that the O key toggles highlight (Over) clipping and the and the U key shows shadow (Under) clipping.
Finally, the only thing that should change when the clipping indicators are on or off is whether you see blue for shadow clipping and red for highlight clipping in the main image area. The triangles should always have non-black color in them if clipping is occurring.
And there being color in the triangles don't always synchronize in blue or red in the image.
Do the blue or red pixel-clipping overlays show up on the image when the sliders are adjusted to extremes (Contrast at max, Exposure at max or min) even though the little histogram triangles remain black, or is there no clipping?
What colorspace do you have set in your workflow options? as asked in the previous reply.
The Lab colorspace takes quite extreme adjustments before it'll show clipping. sRGB is much smaller and therefore easier to see clipping with extreme toning adjustments.
A 32-bit HDR image might not show clipping very easily. An 8-bit non-raw image (like a JPG) will show clipping more easily.
Copy-Paste a screenshot of your full ACR window into a reply, here, with enough extreme adjustments to turn on the red highlight clipping indicator for some pixels of an image. Choose an image that can be publicly viewed on these forums.
The color space setting in camera affects two things:
Because raw camera data has no color space, when you open a raw image in Camera Raw, the Workflow preferences in Camera Raw control the settings of a non-raw format exported or saved from Camera Raw. So if you want Camera Raw to send images to Photoshop at 16 bits per channel in the Adobe RGB color space, Workflow preferences needs to be set up that way.
Additionally, and possibly relevant here: The Color Space set in Workflow preferences controls the color space used to calculate the histogram, and to determine whether clipping is happening. You can see this in action by opening Camera Raw preferences (click the underlined text at the bottom of Camera Raw window), and watch the image preview in Camera Raw as you change the Color Space setting. If there is an area of the image that is close to or slightly clipping in a large color space such as ProPhoto RGB or Adobe RGB, choosing a smaller color space such as sRGB will now indicate more clipping in those areas, because they are now outside the new, smaller Color Space selection. Also, as you change the selected Color Space, you will see the histogram change in the Camera Raw window for the same reason: Both clipping and the histogram are calculated against the current Color Space.