1. this is a follow up to my other post, because i want some more clarification.
2. when working on a jpeg within ACR 4.1 (an overly contrasty image with some highlights blown out, ie histogram to the right), it APPEARS that i'm actually able to bring back some of the highlight data by dragging the highlight bar to the left etc... furthermore, when the image is then opened up into photoshop, the histogram no longer has the highlights bunched up at the right.
3. question: when working on JPEGs via ACR 4.1, is one actually able to recover highlight data? i thought JPEGs had the data already... completely processed etc... what's going on here?
My reading is that highlight recovery isn't just one thing. There are various things that ACR tries to do.
If the data is lost in all 3 channels when converting to JPEG, presumably that is it! (I don't think ACR 4.1 has the "Harry Potter slider" for magic recovery).
But I tried blowing just one channel of part of a PSD image, then converting it to JPEG. Then I opened that in ACR 4.0 to see what the Exposure and Recover sliders (and others) would do to it. They APPEARED to give different values to the blown channel as the value dropped from 255 depending on the values of the other channels. (I had lots of Color Samples set across the image, then watched their RGB values as I manipulated the sliders).
This may have been deliberate. Or perhaps it is a side effect of how JPEG compression works. Or something else entirely. And, anyway, the effect was small in the image I tested. But there DID appear to be a small correlation between the final value of the blown channel and the values of the other channels.