Eric Stevens
On Mon, 21 Apr 2014 20:14:01 -0400, PeterN <peter.newnospam@verizon.net>wrote:

PeterN
On 4/21/2014 6:34 PM, Eric Stevens wrote:

Eric Stevens
On Mon, 21 Apr 2014 09:10:29 -0400, nospam <nospam@nospam.invalid> wrote:

nospam
In article <4v89l9l7jfpgd98oiu0thal6gdao3aab9t@4ax.com>, Eric Stevens <eric.stevens@sum.co.nz>wrote:

Eric Stevens
I've never said it was not destructive.

nospam
you did ask why a conversion to and from lab would matter.

Eric Stevens
I don't think I asked that. I have asked why converting to Lab would require more conversions than to any other working color space. You still haven't told me.

PeterN
For all practical photographic purposes there is no visible differences. Alan Browne has posted some examples in alt.photography. I went a step further, using Alan's images I applied a small curve adjustment in LAB that should have brought some of the darker areas into a portion of the LAB color space that is outside the gamut of the RGB space. I converted the LAB image back into RGB, and saved it together with a copy of the LAB image. nospam was invited by both Alan And myself to duplicate the experiment, and has given nothing but transparent excuses for his failure to post a duplicable experiment.

Eric Stevens
Well, there are all sorts of secondary questions about black point, rendering intent etc with such conversions. But my point is that Lab mode is surely not the only mode PS which requires color conversion and I can see no reason why that conversion should be any more lossy than any of the others.