How Photoshop works with colour
Image > mode identifies what form of image it is (e.g CMYK)
Foreground colour square> colour picker window> colour libraries. This is where the spot colour library is for photoshop. You can also look through a physical reference book for pantone and type this number into this colour libraries window.
The foreground colour square is now this exact colour you have chosen.
When we use spot colours in photoshop - we have to use and apply colour in a different way from what we have previously.
We cant just choose spot colours and apply this to a CMYK image and they use different ways of applying colour.
Using Spot Colour Channels in Photoshop
Start with line artwork that needs colouring in. What we need to do in Photoshop is fill this image with colour separations that we want to use for screen print.
Everything takes place in the channels palette.
Channels palette> small drop down in top right hand corner of palette > new spot channel>
choose a colour that represents the colour we are going to print with.
don't use spot colour reference system because there is no way we can recreate these exact pantone colours when mixing paints from screen print.
Name the spot colour channel to remind us of the ink it is representing. It is also really good practice to include the word "spot" so you know you aren't using CMYK for this.
When working with spot colour channels - overall in the finished product we just need to work with black on the channel as we know black indicates the application of the ink and the amount. A lot of black indicates lots of that colour, white space shows no ink etc.
To make sure the foreground colour black (the little square colour picker in the left tool palette) choose shortcut "D". This resets the foreground square.
Because we chose our colour already - this is what we are painting with. the application of colour in our composition is in this blue that we chose to help us, but the over all final ink in our channels palette is black.
Black foreground colour picker applies colour and white removes it.
When working with channels we can apply colour using our chosen colour but this is in fact creating a black and white "channel" (like a screen print needs).
Any photoshop technique that you apply to layers can be used in channels. e.g selection tools - copy & paste etc.
Double click spot colour channel and this brings up the channel options.
You can change the colour and see what your image looks like with different colours in this way. This is the quick way to do this - as in layers it is a longer process.
Using channels in this was sort of creates layers for us. We can colour in the image without obscuring the black outline for example.
Select > colour range > set values from previous session.
This selection now creates our spot colours for us in this area of selection.
select > colour range. In this area make sure to select an area of block colour in the image. This then selects all the area of this colour in the image for us. Now create new spot channel (channels palette drop down) and change name and colour accordingly.
Switch off CMYK channel to see the area of colour in my new spot channel.
For a screen print positive we need all the pixels to be black or white.
Levels> adjust so there is no light grey anymore. (This will mean the print wont come out properly).
for the next new channel - make sure the CMYK channel is selected and then click select > colour range > and select a new area of the image to fill in with colour. In this case we need to select all the light orange areas.
And for our 3rd channel - Black
Select > colour range
New spot channel
Name the channel
Switching off CMYK in the channels palette - you can now see the channels we created working together to make up the colour separations.
you can select just one of the new channels and clean up any little bits using the white colour selector foreground square. This is to make sure the screen print is ultra clean.
This is using CMYK separations but filling with spot colours.
Make sure when saving that the print is smaller than A3 and that "spot files" and .tiff or .PSD is selected when saving. Any .tiff options just click ok.
Using illustrator to output our positives.
Illustrator (only for files smaller that A3)
File new> make sure it is an appropriate size (a4 is fine for this image.)
Use file place and place our saved image on the new document.
Window > separations preview. illustrator has now pulled through all of the photoshop separations. Click on overview to see a preview of the separations. Turn off CMYK as we aren't using that and now you see the image as it was in Photoshop.
We can check that everything is ok and now we can go to "print" and print our positives.
File>print
We use the same settings that we use for CMYK settings.
Send to black printer and set size
Then choose output, choose separations on drop down and then next to each C,M,Y,K option of separation there is a little circle to the left. Click this and it deselects it from printing. You will now get 3 positives (one for each separation) once clicking ok to print.
For a file that is bigger than A3 remember you cant use illustrator so in photoshop go to the palette channels palette drop down and click " split channels". this then creates a layer for each of our channels in new windows. then just take them won to digital printing.
Once you have split the channels this way - you cannot go back so SAVE A COPY OF THE IMAGE BEFORE DOING THIS. So that you still have the original to work with.
Halftones and tints
Using 2 colours
working with the spot colours - different shades of black, grey and white represent different shades of my ink colour:
select area of image using colour range. create a new channel for this selection and fill it grey (edit>fill. use drop down for grey.
fill this area with a light grey (which represents a lighter tint of our orange)
Select CMKY channels >select > colour range
choose new area of colour. increase/decreases fuzziness so that the colour is cleanly selected. (more or less texture)
Right this has now selected this area for us. so now click off of CMYK channels and go back on our new channel. now you can got edit > fill and fill this new area selection of black.
this enables us to print different tints and halftones on one image.
we can now select our channel and edit/clean up areas of the screen print positive details using eraser/paintbrush etc.
you would then save this as a tiff and open in illustrator and do the same as before.
Except think about print>output levels. frequency and angle of halftones.
if working on a larger scale e.g larger than A3, we would need to split separations in photoshop and use the "bitmap" option in photoshop.
Overprinting or knocking out-(using spot channels)
The way that the inks interact with one another during the printing process.
We can see that the are in which the 2 colours overlap - they create a new colour when overlapped.
Spot colours work in this way because they simulate the transparency of printing ink.
Double click on the yellow channel. solidity value - allows us to change the transparency of the ink. 100% would mean completely opaque. Not see-through.
Once clicked ok - you don't see the effect of this solidarity change.
In order to see this in the composition window. - the layer at the top of your layers palette - is the nearest the front. Spot colour channels work in the opposite way around to this.
Change their order and you can now see the effect of the changes. If purple is put above yellow dots - (Yellow dots represented as an opaque ink)
Change solidity again and you can see the effects once more.
This shows how you can use spot channels to create additional colours during the printing process.
Knocking out:
each separation of colour fits exactly into the spaces left by other separations. in the screen printing process - this is where registration marks come in handy - to make sure each colour separation is printed exactly in the spaces it needs to be.
Over printing.
this helps create additional colours and sometimes tints - just by the overlapping of colour during the screen printing process.
image> mode > CMYK
select > colour range > select the lighter ink. (make sure "white matt" is selected on the preview drop down.
from this selection create a new spot channel. choose colour and re name.
select a new colour range and adjust so that only this area of colour can be seen (using the fuzziness slider). fill this with a darker shade on the same channel so this would create a different shade on the same channel layer.
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