Alan Browne
On 2014.04.19, 20:48 , Eric Stevens wrote:

Eric Stevens
They are quite definite in stating that the Adobe CMS uses Lab space for colour. https://dl.dropboxusercontent.com/u/31088803/CMM.jpg is the diagram included with that section of the text.

I don't know but I suspect that the various modes made available by Adobe to the user only affect the various controls, filters, tools etc made available to the user. In the end they all work on the profile connection space.

If my understanding is correct then it doesn't matter what mode you choose to work in: your image comes in and is converted to Lab. When the image goes out it has to be converted to RGB, CMYK or what ever it is you want. Your choice of mode only affects the various tools etc with which you manipulate the data in the CMM. If that is the case the idea is incorrect that working in Lab mode requires twice as many conversions as working in other colour modes.

Alan Browne
I have no definite answer - but consider that the way the information is stored in memory to work in Lab and RGB may be different and therefore require a conversion. If I load a really large raw (which then is shown to be 16 bit RGB) and then change it to Lab, there is "flash of change" in the image on the screen - as if it has been redrawn on the screen following a conversion.

That could mean: 1) The data was converted and then re-displayed from the converted data.

a) convert the image RGB ->Lab, discard the RGB copy in memory b) display the image from Lab to the display c) image remains in memory as Lab

Or

2) The data was not converted, but was converted on the fly for the purpose of display only - the in-memory copy remains RGB.

a) no conversion b) to display the image, point by point RGB is converted to Lab and then displayed from the Lab data and interpretation c) image remains in memory as RGB

That said, the baseline internal representation might be Lab - so switch things around above as needed.

Given 16 bit representation and the far less than 16 bit capability of our displays, prints/inks and eyes - in the end, for a typical amount of manipulation - and then some - there wouldn't be any discernible loss of information due to conversions IMO.

All that said I don't see a huge advantage to working in Lab directly - though for some "effects" it presents an easy path to fun things. I've tried high pass sharpening in the mono channel in Lab, and while that works, the results are no better than high pass while in RGB. Any particular "betterness" at the pixel level don't show at the whole image level and are not at all perceptible in a print.