Large Format Printing – The CMYK Black Problem

Banner Design

Just recently, a client who’s branding I had done earlier in the year returned to order some printed PVC banners measuring 4ft x 2ft. The branding was such that the imagery and fonts were always backed-up by a black background, to give that ‘dark and sophisticated’ look (get what I mean?). Not much of my large-format artwork consists of flat black backgrounds, but I still thought it was straightforward, to my surprise.

The banners were for an overseas charity project, for which my client is a supporter. The graphic design for the banner simply consisted of the black background, the logo and one line of white text reading ‘Supported and funded by’.

Large Format UV-LED Printing

These were to be printed on a ‘shit-hot, state-of-the-art, wide-format, flatbed, LED UV-cured printer’ that costs more than your house, and also probably looks better than your house(!) Printing at 1200dpi, the output is crystal-clear and sharper than a razor. With the inks dried and cured by UV lamps, the quality and detail is immense. The banner material, which comes in large 50″ rolls, is fed through the printer and it prints directly onto the substrate.

The Problem – When ‘Black’ Isn’t Really ‘Black'(!)

I exported the design as a pdf at 300dpi resolution, and viewed it in Adobe Reader 9.3, it looked fine and the black background seemed really err…black? It looked good. PDF documents are an industry standard type of print-ready file because they hold their resolution and also use the CMYK colour model, which is a popular commercial printing colour model. CMYK is what most printers and commercial-printing set-ups use, which consists of four inks, cyan, magenta, yellow and key (black), which are used in various techniques, to generate millions of other colours and print the artwork.

When the artwork was printed onto the PVC banner material, the print came out such that the flat black background didn’t look black, but more of a ‘dark grey’ or ‘anthracite’ colour. I initially thought it was the printer that fucked up, but these things rarely go wrong so i suspected it was an artwork issue. Photos don’t differentiate in much detail, view the photo below to get my shizzle(!)

I was expecting that rich, dark black but this was a disapointment. I mean, it was ‘nearly’ black, and it was the darkest grey I had ever seen, but, how should I describe this, it was also the ‘lightest’ black I had ever seen, get my drift? My client wasn’t impressed either, so I promised her a ‘full investigation and re-print’ at my expense (very PC Plod sounding I know), but you gotta keep the client-bunnies happy, right? The quest for perfection and quality was well and truely ON..

The Solution – CMYK vs HSV/RGB

I researched around some online forums and blogs, and found the solution to my problem. The problem existed because different colour models interpret flat colours in varying ways. Let me explain. When designing using my vector graphics software, all colours on the screen are viewed and represented using the HSV colour model, which allocates a six-digit code to each colour/shade such as #FF80FE (a glorious shade of pink!). This colour model uses light to generate the different colours on your monitor’s screen, and so are great for web-design and web-graphics.

However, the standard black in the HSV model is represented by #000000, but it’s CMYK equivalent is the ‘dark grey’ black. Yes, it looks fine on the screen, but when converted to CMYK for printing, the various ink mixtures result in the ‘not-so-black’ black(!) #000000 actually converts to C-0% M-0% Y-0% K-100%, which is also referred to as ‘100% black’ because it is 100% of the ‘Key’ black ink which is used.

I was advised to increase the percentages a little on the other three inks. The reasoning behind this is far too complex for a short-ish post on my blog, but it’s related to the way the inks are mixed to generate other colours. I increased the percentages of the other three inks, to create a ‘new colour’ in my graphics software. I opted for C-25% M-25% Y-25% K-100% and used this black instead of the standard black. It still looked the same on my screen, but when printed it was a beautiful, rich ‘darker-than-dark’ black. A huge improvement, and a lesson learned for me. (I don’t have a photo of the improved print because I had to post it out same-day, but it was blacker than black and made the text and font stand out even better). Whooppee!

If you’re a designer, printer or related professional, let me know of any similar problems you’ve had and how you rectified them. If you’re a potential customer, don’t worry, not all my jobs are fuck-ups, this was just a little ‘grey area’ in my skills-set(!)