OUGD504: Workshop 2 - Colour as Ink

The RGB gamut has more possible colours than CMYK.  Certain greens may be outside the range of what you can produce using CMYK inks - by switching image mode to CMYK it changes to the nearest printable colour.

photoshop; be wary of colours in photos that are not within the cymk spectrum
Colours outside of the CMYK spectrum...


convert to cymk lets photoshop pull colours that are print safe and in the cymk gamut

In Photoshop, View > Gamut Warning lets you view the photo with grey areas covering the colours that are outside of the CMYK gamut and will therefore not be able to be printed correctly (as they appear on screen) using 4 process colour.  If this was sent to print, it would choose the nearest colour within the CMYK spectrum to compensate.

Change saturation/brightness/contrast with gamut warning on to tone down the brighter shades that are outside the cymk gamut. These tend to be the brighter areas because the rgb gamut stretches outside the cymk range. Proof colours shows you how it will look when converted to CMYK, but is still in RGB on screen. CMYK file sizes are also larger, and the default way of working is with RGB images.  There's some things you can't do with CMYK images that you can with RGB.

Adobe on Printing images to a commercial printing press:

"Work in RGB mode until you finish editing your image. then convert the image to cmyk mode and make any additional colour and tonal adjustments. Especially check the highlights and shadows of the image. Unmake corrections. Adjustments should be very minor.  Flatten the file if necessary then send the CMYK file to professional printer."

The warning sign appears when a colour is only within RGB spectrum - click top box and it jumps to the nearest colour that is in the cymk gamut. (Bottom box is for web safe colours).

Printing images with spot colour

Select spot colours from Pantone swatches in colour libraries, choosing the selecting that best suits your chosen stock.  The image has to be greyscale to begin with, then select duotone options from the image mode.  By changing 'type' options you can have up to 4 different spot colours to make up the full image.

Duotone:

Two spot colours are used to print an image - select a second colour from swatches.  It's best to keep the name of spot colour in the box for reference.

Change how the spot colour is applied to the original by changing the curves.  You can also change the distribution of inks by checking the overprint colours, which shows us the distribution of colour on the scale of light to dark.

Tritone:

Gives us another colour to strengthen the image and bring the other two spot colours together.

to save:

save as a Photoshop file so it supports the spot colours in the image.


for screen printing:

these separate channels help to work with ink rather than colour - it's helpful to use separate channels as different positives for screen printing

all printing inks are semi transparent (which is how cmyk is printed)

solidity helps to change transparency of ink; simulates an opaque ink on screen

to access the spot colours next time, you must save as Photoshop or TIFF (tick spot colours box)