Understanding how to create, change or mix colours within Photoshop is an essential skill. Fortunately colour management, in general is not a complicated element and there are a few methods at hand to help.
Before we take a look at managing colour, it is important to understand the various colour modes you will inevitably encounter.
Colour modes can be changed for any 8-bit image by going to (menu)->Image->Mode-> and selecting from the list provided.
Grayscale model (Black & White)
Single channel: Although commonly referred to as ‘black and white’, this is not an accurate description of this mode. A Grayscale is capable of holding up to 256 individual shades. These shades are stored numerically and range from black (0) to white (255).
RGB colour model
Three channels: RGB stands for Red, Green and Blue and has a wide range of applications, but most commonly for all forms of screen output. This may include web-sites, video, presentation applications, etc. RGB is additive; that is, full levels of red, green and blue light make white light. The equal absence of these three colours is black.
Each channel can hold up to 256 shades of it’s respective colour. In combination (composite), this can yield nearly 17 million individual colours in a single image. To work this out for yourself: 256 * 256 * 256 = 16,777,216.
Four channels: This colour mode is highly recommend for printable media. CMYK represents the 4 primary colours for ink output; Cyan, Yellow, Magenta and Black. In contrast to RGB mode, CMYK works to the reverse of this additive mode – the more colour your mix, the darker the result. This is known as a subtractive colour mode.
In the same way as with RGB each of the channel carries 256 shades of colour information. CMYK has four channels and can yield up to 429,496,7296 individual colours.
The importance of using the correct colour mode
- The majority of print houses will insist you send your artwork in CMYK to ensure closer colour matching for print. Many will apply an extra charge for image mode conversion.
- Most internet browsers will not display CMYK images. RGB and Grayscale are appropriate modes to use for web and other multimedia.
- File sizes will increase, depending which mode you use. An non-compressesd Grayscale image will be smaller in file size to an RGB and an RGB, smaller than a CMYK if all at an equal pixel dimension.
What are channels?
Aside from storing Alpha selections, Channels are grayscale images, holding (in the case of RGB and CMYK), colour information.
To get a better, hands-on understanding of channels, I recommend opening up the Channels floating palette from (menu)->Window->Channels.
For Grayscale, this palette will prove uninteresting. But for RGB or CMYK, you will see each channel, plus a composite.
Click on each channel in-turn, returning to the composite channel at the top of the palette. You will notice that the tones within your image will change as you do this.
RGB example in depth
The best way to explain how RGB work is with the following scenario:
You are in room with the walls painted white. The lights are switch off and you are now in total darkness. Luckily you have three torches, one with a red light, one with a green light and one with a blue. They are currently all switch off. All you can see is Black.
All switch all on at the same time and point them to the same spot on a wall. What do you see? White! Now switch off the Green and the Blue, and you are left with Red light. Switch on the Green as well as the Red, you see Yellow.
The pixels within each channel work like this, but they have built in dimmer switches to mix more than just the primary and secondary colours seen in the above experiment.
Mixing colour with the Color chip
This is the most immediate method for mixing colour. The colour chip (bottom of the Tool palette), displays the current active foreground and background colours.
- Click on one of them to bring up the Color Picker.
- Choose a color from the vertical color gradient (fig.B)
- Choose a shade from the square gradient (fig.A)
- Visual representation of the current and new colour (fig.C).
You can also mix your colour manually with the various colour mixers: HSB (Hue, Saturation, Brightness), LAB, RGB, CMYK and ‘#’ (Hexadecimal colour for web use).
The Colour Libraries (fig.E) will open predefined colour systems, especially useful for print. This includes all-important Pantone color library. You can revert back to the Color mixer by clicking on the Picker button.
You can also use the Color floating palette (menu)->Window->Color to mix your foreground color.
To select a colour from an opened image or graphic, use the Eyedropper (I) tool on the Tool palette. Sensitivity to selection can be altered from the Options bar, once this tool is active.