Eric Stevens
Fraser, Murphy and Bunting (Color Management) regard Lab as the work horse of color management systems.

nospam
it is, but photoshop doesn't work the way you think it does.

Eric Stevens
Maybe so but you have yet to explain how you think it works and how working inLab mode requires twice as many conversions as working in RGB.

Wikipedia http://en.wikipedia.org/wiki/Lab_color_space says

"Because Lab space is much larger than the gamut of computer displays, printers, or even human vision, a bitmap image represented as Lab requires more data per pixel to obtain the same precision as an RGB or CMYK bitmap. In the 1990s, when computer hardware and software were limited to storing and manipulating mostly 8-bit/channel bitmaps, converting an RGB image to Lab and back was a very lossy operation. With 16-bit/channel support now common, the loss due to quantization is negligible."

But none of this explains why you think Lab requires extra color conversions.

nospam
yes it does.

Eric Stevens
As above: please explain why.

This is the third or fourth time of asking. I'm not trying to argue. I'm trying to find out.