Today’s Question: It was suggested to me that instead of using the saturation sliders in Lightroom, Adobe Camera Raw, or Photoshop, that I should convert my photo in Photoshop to the “Lab” mode and then apply a curves adjustment layer to the ‘a’ and ‘b’ channels. When I do this it seems to me that I’m really getting more of a contrast adjustment like I would in the ‘RGB’ mode with a curve. It probably is a little more saturated but the contrast is also there. What are your thoughts?
Tim’s Quick Answer: My recommendation would be to make use of the Vibrance and Saturation adjustments, rather than converting an image to Lab color mode (and then likely back to RGB).
More Detail: There are many adjustments that can be applied to great effect in the Lab color mode in Photoshop, in some cases providing an advantage over the RGB color space. However, quite often I find that the advantages are minimal, and not without risk.
For example, in this case I suspect you are applying an unbalanced adjustment for the two channels, resulting in more of a contrast (or color contrast) adjustment rather than a saturation boost.
Even if you applied a perfect adjustment in Lab using Curves in order to boost saturation, as far as I’m concerned this would provide no real advantage over simply using the Saturation or (even better) the Vibrance adjustment. Both of these adjustments are quite sophisticated, and have been updated over the years, so that there isn’t a real advantage in this case to switching to Lab mode.
In short, I’d suggest keeping your workflow relatively simple, and not be tempted to “tricks” that aim to provide marginal gains that you may not even be able to perceive. Worse, switching to a color mode you aren’t particularly familiar with could cause challenges in terms of maintaining quality and fidelity in your images.
It is worth noting, by the way, that switching to the Lab color mode and then back to the RGB color mode could itself lead to minor alterations in pixel values that could be somewhat problematic, and that would negate any gains you might have obtained by using the Lab color mode in the first place. So, I suggest sticking with the RGB color space and the very good Saturation adjustment and the (even better!) Vibrance adjustment.