Re: CT to LW trapping
Well, it depends.
Let's say you have an RGB document that has the type built (say black type RGB 0,0,0). You convert this to CMYK, and the type goes four-color. Then it doesn't need trapping because it has all four colors. This is what also happens if the type is RGB black and is placed into InDesign and converted upon output to CMYK. Whether converted in Photoshop or InDesign, any RGB black will become four-color.
Let's say you have a Photoshop document that has the type, when it gets rasterized, it will all be CT, right? Let's say the type was 100% Cyan, and the background is 100% Magenta. Well, if you zoom in real close, you will see that there are some pixels that have both Cyan and Magenta. So being a CT, it's already trapped (as long as the trap required is around .003", because 300 pixels per inch (resolution) x .003 = .9, so really 1 pixel trap needed in my case, and the slight overlap of colors made by rasterizing creates enough trap for me). This is the option that happens if the file is CMYK before placing into InDesign.
Let's say I have a trap I want to make in Photoshop (because I need more than .003" trap). I can do this manually by going to Image menu and choosing Trap... which will bring up a box to specify what amount of trap needed. Note: Say you have a spot color job and want a lighter channel to trap into a darker channel. You would select the lighter channel in Channel palette, and deselect the darker channel, then choose the trap option, which will only spread the lighter color into the darker.
And of course there's the option a prepress person has of trapping in the rip and choosing the option to trap CTs, which would also trap this area if the rip saw it as untrapped. I usually leave this option off for a couple reasons, but do manually turn it on if I feel the job warrants it.
Don