Opening JPEGs in ACR 4.6X

[robbie_robertson]

<p>I searched the archives earlier today on ACR and JPEGS, and found a string from 2007 that touched on my question, but was mainly speculation instead of solid answers: I use 'Open As' in Elements 6.0 to open a JPEG in ACR 4.6X (the Beta version created just after the D90 was introduced). While not allowing the latitude of adjustment I get with RAW images, I get a much greater latitude of adjustment than if I simply opened the JPEG in Elements, and greater latitude remains after I transfer the image into Elements from ACR. I found a greater range of white balance adjustment and tone changes in ACR, and the same with adjustment layers, contrast and sharpening when I transfer into Elements.<br>

What I (barely) understand is that ACR is working at greater bit depth, but if it's opening an image that was saved at 8 bits, isn't that the limit I could be working with? What, something just under 5000 shades? If I open a JPEG into ACR, does it change the color space to Adobe RGB (my working color space) allowing greater latitude before resaving into sRGB as a JPEG? The success I've had in reworking old flawed JPEGs in this manner is great, but I want to understand what's going on here. I would greatly appreciate answers based in solid technical understanding. I apologize in advance, but would like to ask that conjecture not be involved in responses. My head is already full of conjecture (among other detritus) as it is... :-)</p>

[digitaldog]

<p>When you open a JPEG, its converted to high bit, ProPhoto RGB primaries and all metadata edits are then applied to that data in one "convolution" so to speak, in the preferred order. So yes, while the toolset is more limited than Photoshop proper, good quality camera generated JPEGs may in fact produce a bit better quality than doing the same/similar operations in Photoshop. Plus its faster. How you export the data (in ACR, the settings of the workflow options) decides bit depth and color space on the way out. </p>

<p>This might help too:<br>

http://www.ppmag.com/reviews/200701_rodneycm.pdf</p>

<p>Lightroom and ACR share the same processing engine. </p>

[robbie_robertson]

<p>That's the answer I needed. Thanks Andrew! </p>