Colour is perhaps the most important element in printing. It is what people will see and experience before they even touch the paper. For this reason, it’s important to make sure that we keep our colour quality to a high level so that our customers can get the best quality printing available.
CMYK vs RGB
Perhaps the biggest confusion we see here at Q print Group is the difference between CMYK and RGB. In its simplest form, RBG and CMYK are types of modes for mixing colour. The easiest way to differentiate them is that RGB colour is used for digital artwork and CMYK is for printed products.
RGB
RGB is an additive colour profile where the primary colours of white light (Red, Green, and Blue) are added together to create new colours. The main thing to remember about RBG colours is that they can only be produced by devices that generate light; like computers, phones, and televisions.
Green and Blue light create Cyan
Blue and Red light create Magenta
Red and Green light create Yellow
Red, Green, and Blue light all together create White
Colours are created by the light of a device mixing the red, green, and blue to varying intensities. This style of colour mixing is called ‘additive’ because all colours begin as black and the red, blue, and green (on a scale of 0 to 255) are added on top of each other to brighten the screen to create colour pigment.
RBG is similar to how our own eyes perceive colour which is why it has such a large colour gamut. Our eyes have three different cone cells in our retinas, each perceiving either red, green, or blue. Our brain absorbs this light information from our eyes and combines them to create all the colours that we can see.
Design software often works in RGB as the default colour mode because it is the most accurate colour profile. If the artwork was going to be purely digital, the designer would use the RGB colour mode. If, however it was going to be printed, the designer could either convert the final image to CMYK or change the colour profile to CMYK before beginning the designing process.
CMYK
Printed items do not generate their own light and can only reflect and absorb the light that hits them, this is why CMYK is a subtractive colour profile. To get a bit technical with it, inks work by absorbing all colours from light other than their own which they instead reflect. The process of colour subtraction involves the primary colours of light (RGB).
For example, if white light (like sunlight) is shining on a yellow shirt, the shirt absorbs the blue and reflects the red and green which together create the colour yellow (as seen on the RGB colour circles)
But what if a cyan light was showing on the same shirt? Well the two colours in a cyan light are Green and blue, the same shirt would absorb the blue, and in the absence of red from the light, will instead appear green.
So how does this relate to CMYK colours in printing? Well understanding how the light is absorbed and reflected shows the relationship between RGB and CMYK and demonstrates why we get certain colours when we mix CMYK colours.
Magenta and Yellow ink combined only reflect Red light
Yellow and Cyan ink combined only reflect Green light
Cyan and Magenta ink combined only reflect Blue light
For example. When you mix 100% Yellow and 100% magenta you would expect orange right? Well no, you actually get Red. This is because of how the CMYK colour circle is the inverse of the RGB one.
CMYK is used for print because print does not generate its own light and therefore needs to absorb and reflect the light to create colours.
The disadvantage of CMYK is that is doesn’t have as wide a colour gamut as RGB. This is because CMYK only has a scale of 0-100 (% of ink being used). CMYK also cannot reach the more fluorescent colours seen with RGB, especially with yellows and greens.
When creating print designs, it’s a good idea to design using the CMYK colour gamut as this will give a more accurate visual of what will be printed. Designers can often be disappointed if they created a design with vibrant colours only to have that design printed and the colours look more muted than they expected. To make up for this weakness in CMYK, there are special types of inks called Pantone and Spot colours.
Pantone and Spot Colours
Spot colours are specific colours that can be exactly reproduced every time they are printed. They are traditionally premixed inks for that specific colour. The Pantone colour matching system is the most common way to match specific colours.
Due to the premixed nature of Pantone colours, they are able to reach a wider colour gamut than CMYK and can help to fill in the gaps where CMYK cannot reach the same level of colour intensity as RGB. Pantone colours can be indicated by using a pantone code such as PMS 136 or PMS 227.
Pantone colours are great for when you need a very specific colour for logos and corporate branding, but do tend to be more expensive than just using CMYK inks.
Metallic and specialty inks (like opaque white) also are classed as spot colours as they cannot be reproduced with standard CMYK inks.
Colour Matching
Due to the nature of printing with CMYK inks there can be a small degree of colour variance during the printing process. This means that colours on the same artwork can look slightly different from the beginning of the print run to the end, with the colour variance becoming more pronounced between runs of the same artwork.
In digital printing with toner, this colour variance is mostly due to a change in temperature. Due to this fact it is important to be constantly checking the colour throughout print run and making changes to the machine as needed. Our print technicians are expertly trained to notice even the slightest shift in colour so they can return the colour to its true form.