MONO E-LAB-ORATED

Canon G1X @ 60mm (105mm eq.) w/polarizer
Square-cropped, lab-unsaturated and slightly level-tweaked out-of-camera jpg
1/640" f5.8 ISO 100

I'm frequently using LAB color method in order to turn my images into monochrome. I first convert the file into LAB, then I dump a, b and alpha 2 channels, just preserving alpha 1 (i.e. luminosity). This way I avoid the hassle of some artifacts appearing, for instance, in blue sky areas when converting into monochrome via the usual Photoshop color mixer.
What amazes me in this process is the increase in overall sharpness of the converted image, especially in the details. My technical knowledge doesn't go far enough to understand why. So I'd be grateful to anyone explaining to PhotoGraphia readers and myself why a LAB-converted image is (or looks) sharper than an RGB unsaturated one.
Thank you in advance. 

Comments

[Stefano Mazza]

From my own part, I don't have a great colour space knowledge and I'm not a digital B&W expert, however I know that is generally accepted that Lab workflows are less disruptive than RGB ones.
I fear that the answer is not simple and is to be searched in the physical and informatic models that are applied to both methods.
Though RGB colour space is very close to the human eye colour perception, Lab colour space is based on a non-linear relationship between the three L,a,b parameters, that fits better the human eye response to luminosity and colours. This is perhaps the main reason why the overall perceived image quality is higher and, as a consequence, sharpness is also better than in RGB.
I also suspect that many advanced B&W converters (like PercepTool for Photoshop or c2g in Gegl/Gimp) have Lab-based engines.

For instance, I can tell you that colour analysis in test laboratories are often performed in Lab parameters (which is also called Minolta-colour analysis).

Very interesting topic, I wish to hear other answers.

[Gianni Galassi]

Stefano,
thank you for your well-informed reply.
I was suspecting something like this and I should have gone searching the Internet for a better knowledge.
But I'm just starting my summer vacations and I feel too lazy to actually "study" this matter.
Therefore any abridged explaination will be more than welcome.

[Nicolas]

Hi Giani,
Let read here, great clever tips: http://landscapist.squarespace.com/journal/2010/7/28/civilized-ku-597-99-printing.html
Kind regards
Nicolas

[Gianni Galassi]

Nicolas,
you are right, Mark Hobson's post is quite interesting and I suggest PhotoGraphia readers to read it as well.
Thank you for pointing it out.