Lurking in the darkest, deepest corner of Photoshop CS6 is checkbox and a text field that control the appearance of text antialiasing. They can be found by opening Color Settings under the Edit menu, then by clicking More Options.
Blend Text Colors Using Gamma is brand new for CS6. It’s a global option, not per document, and applies gamma correction to text layers, making them look thinner or fatter, depending on the value.
A crude approximation of what’s happening can be seen below. The text’s mask is being processed by an input-output curve. Black remains black, white remains white, but the grey pixels, the antialiased areas, change in contrast and brightness. (Sincere apologies for all the animated images, but it seems like the best way to show the subtle differences.)
As well as altered text antialiasing, Photoshop CS6’s default behaviour changes text layer opacity. I assume this is because the text mask is initially drawn to match the opacity required, and then the input-output curve is applied. This results in Blend Text Colors Using Gamma changing the antialiasing and layer opacity, which probably isn’t desireable.
And, because Blend Text Colors Using Gamma didn’t exist in Photoshop CS5, text will look different when you open up your older documents in CS6. Different, and slightly lower opacity, for non-opaque layers.
It’s also a little worrying that text and shape layers that are the same colour and transparency won’t match, unless Blend Text Colors Using Gamma is off.
I recommend disabling Blend Text Colors Using Gamma.
Hat tip to Max Rudberg and David Jensen for finding the option. There’s more CS6 text gamma discussion on Adobe’s Photoshop Feedback site. Feel free to ask me questions via Twitter (@marcedwards) about this article.