CMYK Vs RGB Printing
Remember many years ago, one night we were rushing a packaging box printing for our client. We invited the designer to drop by our factory and have a look at the printed colours.
The designer took out his powerbook, compare the printed colour with the colour on the screen and question why the colour were not accurate. We have to explain that the laptop monitor is in RGB colour and packaging box printing is done in CMYK. No way that the packaging box colour will look similar.
We can’t blame the designer, working for an International agency, and he might have used his laptop screen to show his customers and they insisted that that is the packaging box colour they want.
But in reality, CMYK printing we can never get the RGB colour on the laptop screen no matter how good is the laptop screen or the offset printing machine.
What is RGB Colour?
RGB are the colour used for electronic display screen such as colour monitor, smart phone, ipad and our television. Red, Green and Blue stand for:
R = Red
G = Green
B = Blue
In electronic display screen, these 3 main colours are mixed together to create the various range of colours that you can see on screen.
If you are a web designer, which you only used a computer screen to do your work. You can use RGB colour without worrying that the colour will look different.
Only the other hand, if you use RGB colour image for CMYK printing, the outcome of the image will look dull as though that there are not enough black in the image. And these will make your printed material look very bad.
Because there are only 3 colour being used, RGB is always smaller in terms of file size when you save it in the computer.
What is CMYK colour?
CMYK is the colour used by printers to do printing. It is made up of four colours:
C = Cyan
M = Magenta
Y = Yellow
K = Black (Key)
Like colour palette you mix magenta (M) and yellow (Y) to get red. Cyan (C) and yellow to get green and cyan (C) and magenta (M) to get purple.
In order to get a darker colour, you apply more black (K) and you will be able to get a darker blue, red or green. You can also get a more solid black by adding 30% cyan, magenta and yellow to black. Key is simply another name for black.
CMYK file is larger when you save it in the computer.
Use CMYK for colour adjustment
When I was an art director, I always go to colour separator to check colour on their high-end monitor which have been calibrated to match the offset printing machine.
They told me to use RGB and photoshop image adjustment to do colour adjustment and then only convert the image to CMYK, and do further adjustment.
I have been doing that for many years, until one day my colleague in Uniquelink say that normally when he received the images, he always change the images to CMYK so that no RGB image problems will occur during printing and he used CMYK to adjust the image.
Today I always convert the images to CMYK first and do the necessary adjustment because I believe my colleague is right. If you follow this step, RGB image problems can be avoided.
How to do colour adjustment?
We normally used photoshop to do colour adjustment. To explain it in a very simple way, first you changed the image to CMYK. If you find that the image is bluish, reduce cyan. If you find that the image is reddish, reduce magenta. And cut down the yellow if the image is yellowish.
When you are happy with the colour make the colour slightly more contrast by using the colour adjustment. Tick the middle of the line and make it slightly curvy, right higher and left lower will do.
It is always better to make the image slightly more contrast so that if will stand out when printed.
If possible, always used a better colour monitor like Viewsonic for colour checking. Colour accuracy although not 100%, but up to 80% will be good enough. A good colour monitor will help you with colour accuracy for printing
Fonts should have no colour after you unselect black in separation preview.
The Common Mistake?
Apart from the RGB images that will look dull, The other common mistake that we encounter are the fonts are in CMYK black.
Especially when you convert low resolution pdf to illustration, make sure you check whether the black are solid or in 4 colours. You cannot tell by just looking at the screen because it is in black colour.
The only way is to check is with illustrator. Select Window separation preview and unselect black. You will see other colours in the black fonts.
Printing packaging box or brochure with CMYK black will look very funny because the black will have other colours which will be very unprofessional.
Conclusion
Technology have help us in preparing our file for printing. Today we normally received artwork in high quality print pdf and they will automatically convert the images to CMYK. Having say that, if would still be better to adjust the CMYK and make the image stand out.
Whether you are printing packaging box, brochur or leaflet, we will always check your artwork so that the printing is smooth and in high quality.
If you have any questions regarding RGB and CMYK printing. Give us a call, we will be happy to answer any questions you have.