The effect of + and - before options

[djd]

In another post, snibgo mentioned something of which I was not aware but is useful to know. Snibgo wrote:
"Most, if not all, settings have "+" option to set the default value."

If this is the case, then maybe `antialias' is an exception as when creating an image, the default behaviour is to antialias the edge pixels and +antialias turns off the antialiasing.

[fmw42]

The + and - options can work differently for different functions, unfortunately. And in the case of antialias, it seems to be backwards from one's assumptions about + adding and - subtracting. Typically - enables the option and + disables the option. However, for example, -distort produce output of the same size as the input, whereas +distort can create a larger output. Not all options or settings have a + form.

[snibgo]

Yeah, I should scrub that statement, and replace it with:
"Some settings have "+" option to set the default value."

Other settings where "+" doesn't restore the default include: depth, dither, format, fuzz, and probably others.