[Gimp-developer] lgm talk, part 2...

[Chris Mohler]

On Sat, Jun 20, 2009 at 11:27 AM, yahvuu<yahvuu at gmail.com> wrote:
> hi,
>
> Chris Mohler schrieb:
>> Imagine I'm designing a black t-shirt with say five spot colors,
>> including white.
> [..]
>> Whew ;)
>
> Whew, too ;) Makes me wonder if it has to be that hard or if
> it points to some missing software improvements. Trying to understand
> the example, i hope you don't mind some uninformed questions (and also
> some out-of-sequence quoting).
>
> Besides anticipating printing press idiosyncrasies ('choke'),
> it seems to me you're manually creating kind of a color separation.
> Quite naively: doesn't photoshop know you're printing on black?

Yes - I end up doing a lot of it manually, and no it does not know -
having a 'target' or 'base' would be a step forward.

>> Here's my workflow for this in PS: I would use the (badly named)
>> 'Apply Image' command to take the contents of each color plate and
>> combine them into the white plate using the mode 'multiply'.
>
> this is to create the white underpinning, resp. the beginning thereof.
> 'Apply Image' is short-hand for 'blend anything with anything',
> but doesn't do any tricks that could not be achieved with layer stacks
> in combination with proper channel masking. On track?

Yes.

>
>> I would
>> also manually "choke" the white plate - this means making the white
>> areas a point or two smaller than the colored areas, thereby
>> preventing the white from poking out at the edges of the colored
>> areas.  This process can get a bit tricky, especially if the original
>> artwork is very complex.
>
> if the artwork was fully vectorized, say a pure inkscape job,
> would that make things easier?

Of course, but when photographic-type artwork comes into play, it's
usually easier/faster to do the whole thing in a raster editor.

>
>> Often, create temporary layers (or plates),
>> perform selection/drawing functions, then combine the result back into
>> a plate in one of two ways - either making a selection on the temp
>> layer and going to the plate and filling or erasing, or using the
>> 'Apply Image' command to take the RGB channel of the current layer and
>> combine it with a plate using a mode such as Multiply, Screen, or Add.
>
> i assume the temporary layers are mostly grayscale?

Usually RGB layers, or grayscale channels.

> the temporary layers serve as 'mixing stage' because it takes
> several steps to create a desired mask, or is it more
> to keep selections/drawings for reuse?

A little of both.  Sometimes I just need a very complex selection, but
I need to do some work to create the selection.  Other times I need to
store a selection for later use  (that's generally when I make an
extra channel).


After re-reading the notes on the talk, if we have a Layer->Plate
mapping, I think that will cover most situations.  I would prefer a
way to "mix" the plates, and to be able to add new layers that could
later be applied to new or existing plates, but this could be worked
around.

Chris