heres another example of separating in sections for clarifacation.

the image above was sent to me as a 5x7, 200DPI jpeg to be upsampled and printed at 15.5x18 with 10 colors. it was reduced to 160 DPI and the print came out pretty well.

the black with yellow outlines image is an example of how i separated the image into color sections. each section is separated with the minimum needed colors, so they will not be dirtied up by the other colors. this can be tedious, but if you knock out the paths/masks you'll save yourself alot of frustration cleaning up the separations. (example... section 2 was only separated with blue, light blue, and white, nothing else. section 6 was separated with black, white, yellow, and gray)

so make sure to separate (as in layers, not index separate) your image into sections, whether it be during creation or afterwards with paths so it will be easier to indexs separate later.

observe the image above. saturating the image is necessary to make sure that gray or a midtone color will not dominate the majority of the index dots. it is a learned skill as far as knowing how much to saturate. in the meanwhile, one can take the flattened rgb and convert to index and investigate. if the index pattern seems to be dominated by one color, you could just as easily undo and index again. most of the time i will index an image, drop everything into channels to see where the problem areas are. once you get the hang of it, it shouldnt take much time.

lets skip to the point where we have indexed the image and dropped the colors into the channels.

heres an example of what happened to the gray plate.

the left image is the gray index channel. the right is the manipulated one. i took an airbrush and manually cleaned up the plate. whats cool on a dark shirt, which would have a base white, is that the base white will take place of where the gray ink should be.

another reason i knew where to take the gray index out is i had all the colors laid out in the channels. i usually place the gray plate near the top of the channels palette which means it will be printed early on. with all the colors turned on in the channels except RGB, if you toggle the trouble plate on and off, you can see where it is needed and where it is not. turned back on, i took an airbrush and erased the pixels where i did not think the gray index dots were unneeded.

above is the black plate. left is original. right is manipulated. black has a tendency to heavy up, so just as the gray plate, i erased some of the pixels anticipating the dot gain. in the red 1 area, the black ended up fine. in the blue 2 section however, after printing, there was no contrast between the shadow underneath the car and the valance. it all turned black. in hindsight, the pixels should have been reduced approximately 70% more.

lets make base white.

to make base white, take the original non-index mode rgb layer, and use Image > Adjsutments > Selective Color > and take the Black out of the Red, Yellow, Orange... any colors that would need a base white. Royal blue, and red need to be reduced down quite a bit, as when one desaturates an image, they do not desaturate as much as other colors. see how much black i took out of the rgb layer on right.

after adjusting the black, desaturate, inverse, and use levels to make sure the middletone is leveled out to make sure ink will not be in the shirt area. this is also the same method to create highlight white except you will use adjustments to darken areas like red, yellow, etc.