Adobe Camera Raw 12.3 Histogram

[GrahamH1]

I'm trying to find out how to change the Camera Raw Histogram from RGB to show the Luminosity graph.  Adobe Help can't answer me.  Any help very welcome, thanks.

[D Fosse · Accepted solution]

Can't be done AFAIK.

The ACR histogram shows the data as encoded into the output RGB color space you set in the workflow options.

Luminosity is a Photoshop-specific formula that doesn't directly relate to any standard color space. It is similar to Lab L, but not identical. The actual formula is a weighted mix of R, G and B.

[TheDigitalDog]

You may want to check out the Histogram on the Curves panel.

[elie_dinur]

Right-click on the histogram and select "Show Lab Color readouts."

[TheDigitalDog]

The ACR Histogram shows RGB and luminosity as seen below left (and you can see Curves shows just luminosity). 

Compare the white part of the Histogram to the final image Histogram in Photoshop set to luminosity:

ACR HistogramsPS Histogram from the raw