This may be old news to many of you, but I just stumbled on to it and nailed it down. The new(ish) Lightroom exposure control (Process Version 2012) works differently than the Exposure adjustment layer in Photoshop CS 6. While the Lightroom control gives you a convenient way to simulate the shoulder of the film DlogE curve, the Photoshop control works more like the old Lightroom Exposure control (Process version 2010).
I created a 1/3 stop step wedge in Matlab:
I added a gamma of 2.2, and converted the image to 16 bits per color plane, and wrote it out as a TIFF. I imported it into Lightroom as an Adobe RGB file, and exported TIFFs with the Exposure Control set at 0, +1 EV, +2 EV, +3 EV, and +4 EV. I brought those images into Photoshop and measured the L* (the luminance channel in CIELab) component of the leftmost steps in each image. Here’s what I got:
You can see that the Lightroom Process Version 2012 exposure control tries to avoid blowing out the highlights, unlike increasing exposure in a digital camera. I consider this to be a good thing.
Next, I brought the step wedge into Photoshop CS6, added an Exposure adjustment layer, and observed the L* values with the Exposure control set at 0, +1 EV, +2 EV, +3 EV, and +4 EV. Here’s what I saw:
The Photoshop CS6 Exposure control works more like actually increasing the exposure in a digital camera.
Which is the better way to develop deliberately underexposed images made using “ISO-less” or Unity Gain ISO exposure methods? The PS way is better if you’re trying to simulate what you’d get if you just turned up the ISO, but the Lightroom way is better if you want soft clipping of the high values, like you get with film. What should be your default? Seems like a no-brainer to me; I’m going to go for PV2012 and later unless I’m doing numerical experiments.