Just started to try to compile some related information,
from current articles and earlier discussions (as referenced below).
From left to right along the tonal scale:PV 2010: Blacks Fill Light Brightness Recovery Exposure
.PV 2012: Blacks Shadows Exposure Highlights Whites
/> The former Exposure slider was renamed to Whites.
Still, the slider moves the White point. Not sure though, if it is really just a rename with regard to operations in terms of linear scaling, corresponding to +/- EV camera exposure (need to check).
and Fill Light
were replaced by improved functions called Highlights
With the new Highlights control there is some automatic Highlight recovery going on, even without moving the slider away from zero, or using the Auto button.
With the new Shadows slider in PV 2012 its effect got more limited to the darker tones, while applying an improved algorithm to brighten without posterization.
is called Blacks
again, now featuring an auto-calculated Black point at default zero setting.
Still, the slider moves the Black point. Not sure though about possible changes under the hood with regard to operations in terms of applying a linear offset (need to check). Interestingly, the new Blacks slider was shown to bear a reduced side effect on color saturation.
/> Former Brightness
sliders were hybridized to the new Exposure
which now mainly controls the midtones, but also moves the White point. It is to note that already at default zero setting* the highlights are compressed, and further with positive settings to brighten the image.
/> The Contrast
slider is now scene-dependent, offsetting its operational midpoint depending on whether you are editing a low key or high key image.
*PV 2010's default settings had Brightness +50, Contrast +25, Blacks +5, and a "medium contrast" Point curve applied. With PV 2012, results are quite similar with all the sliders left at zero now, and Point curve = Linear. The deviations are due to automatic Highlight recovery, and the auto-Black-point functionality, which are always enabled behind the scenes.
Anyway, the default settings impose an "S" curve on the tones, which already compresses highlight details [which is probably the main reason why some of us liked to start with a linear, flat, scene-referred rendition in the past. A subject on its own, I guess].
All six tonal controls in PV 2012 are image adaptive. They auto-adjust their behavior internally based on image content, just like Recovery and Fill Light (and also Clarity) already did with PV 2010. In PV 2012 this idea was extended to the rest of the central Basic controls from Exposure to Blacks.
Comments and additions are welcome.
Charles Cramer, Tonal adjustments in the age of Lightroom 4http://www.luminous-landscape.com/techniques/tonal_adjustments_in_the_age_of_lightroom_4.shtml
Martin Evening, Extreme contrast edits in Lightroom 4 and ACR http://www.dpreview.com/articles/1205103502/extreme-contrast-edits-in-lightroom-4-and-acr-7
Why "0" should be Zerohttp://forums.adobe.com/message/4289492#4289492http://forums.adobe.com/message/4128876#4128876http://forums.adobe.com/thread/948951
ETTR, Blacks & Exposure settings vs. Point Curve controls (PV 2010)http://www.luminous-landscape.com/forum/index.php?topic=57177.0
late edit: cancelled some lines for archival purposes