Hopefully you’re starting to get the hang of things when it comes to images and pictures, but there’s still one final thing we need to discuss: Colour.
Have you ever had a photo look spectacular on your camera, phone, or computer screen, only to have the colours look totally different when you print it out? Why does my family photo look bright and lively when I’m editing it, but it looks dark and dingy off my inkjet printer?
To understand why this happens, we need to talk about colour and how it works, and the ways we use different colour system. Let’s start with the basics: RGB and CMYK
RGB stands for red, green and blue which are the primary colours of light, and combinations of those colours of light are combined to create other colours, including white. The absence of any light is black. RGB is called an additive system (colours are combined), but the colours are emitted from a light source, like a monitor, camera screen, a light bulb or even the sun. Our eyes absorb the various wavelengths of emitted light, and that’s how we perceive colour. The device you’re using to read this is using the RGB colour system to produce the colours that you see, and nearly all digital cameras default to using the RGB colour system when they produce images, because that’s how electronic devices display colour.
To express a colour value in RGB, we need to know the amount of red, green and blue, and the ranges for those are from 0-255. To create yellow, we need a value of 255 for red, 255 for green, and 0 for blue. That will create yellow light.
Process Colour (CMYK)
Things are different when we put ink on paper and other substrates. Those surfaces create their own light, instead the light bounces off or passes through them and then reaches our eyes. To reproduce different colours on those surfaces, we use pigments to create inks that absorb different wavelengths of light, allowing only certain colours to reflect off/pass through them to reach us. Since the inks absorb colour, this is called a subtractive colour model, and the primary colours of this system are cyan (C), magenta (M), yellow (Y) and black (K). Combinations of these four inks are used to create the printed spectrum. Having a high concentration of all the colours makes a rich, deep, black. If there’s no ink at all, then the colour of the surface is what we see, which most times is the white of the paper we’re printing on. This is the exact opposite of how RGB and additive colour models work.
To express a colour in the CMYK system, we say what percentage of each colour we need. For a pure yellow, we need 0% cyan, 100% yellow, 0% magenta, and 0% black.
What you’re putting the CMYK inks on to matters as well and can affect how the colours appear. Gloss coated paper has a layer of fine clay (or other materials) applied to it, to give a shiny appearance, and this coating gives the paper a reflective sheen. The layer also allows the inks to sit better on the surface of the sheet this makes the colours to be bright and vibrant, which is why that kind of paper is used in magazines and in the photo quality paper you may have for your inkjet printer.
If we try to print that same image, using the same CMYK inks, on a sheet of regular, uncoated bond stock, like we print our emails on, we instantly see the difference. A sheet of paper without a coating absorbs ink much more readily, and the ink spreads farther. This causes the image to be darker, duller, and often fuzzy. So, now we can see why we’re likely having issues with the photo from our digital camera (produced in RGB), displayed and edited on a computer screen (which uses RGB) and then printed on our inkjet printer (using CMYK inks), on an uncoated sheet of bond paper (which absorbs ink heavily and makes things darker).
What are some simple things we can do to fix this?
- Use software to convert our photos from RGB to CMYK before printing, so we can see how the image colours will shift, and we can adjust
- Use coated paper stocks specifically designed for high quality CMYK print production, instead of uncoated paper
These won’t correct all the issues, but they are some simple things you can do to help improve things. And if you’re working with a commercial designer or print shop, having your photos already in CMYK format, with the proper resolution, and in a suitable file format, will save you time and money in the long run.
What do we do though, if a specific colour is so important, that it has to look the same every time it’s used?
Spot Colour (PMS)
Sometimes its critical that a colour is printed correctly, and that it’s the same every time it’s produced, such as with a company logo. One of the easiest ways to do that is to have specifically mixed inks for that colour. The most widely used ink system is the Pantone Matching Systems (PMS), and each Pantone colour has a specific pantone number. Inks are shown in a swatch book, like the paint swatches you get from the hardware store.
Offset printers can order pre-made PMS inks for each specific PMS colour, or mix them in house to match PMS specifications, and by using these inks, can reproduce colours consistently for every print run.
It’s important to remember that, just like with CMYK inks, the stock you’re printing on affects the results. Uncoated stocks absorb more ink than coated stocks, so there are two separate sets of PMS colour charts, and you can see how your PMS ink will look on both types of paper. You may need to choose a different PMS ink for each use, to achieve the same colour result.
The final colour system we’ll discuss, is the HEX colour system, or hexadecimal colour. HEX is a shorthand way to express RGB colours in an easier way, and it’s used specifically for web design. Instead of having to say we want 255 red, 255 green, and 0 blue to make yellow, we can instead us a six-digit combination of letters and numbers instead, which for yellow is #FFFF00. That way, specific colours have specific codes, and it’s a much easier way for web content creators to manage colours. If you’re not involved in internet content creation, you may not run into HEX values, but it’s good to know what it is and what it’s used for.
So, there you have it, a crash course in image formats, resolution, and colour formats. While we couldn’t possibly cover everything, hopefully we’ve given you enough information to help you have a clearer picture and make your next print project just a little easier.