You can call it “SCTV” or “Spot Color Tone Value” or “ISO 20654”. But regardless of what you call it, this is a topic that has created a lot of buzz in our industry over the last few months. However, despite all of the buzz and media coverage, there still seems to be a lot of questions about what is it and how it can benefit printers. So here’s a quick explanation that will hopefully demystify SCTV and explain why you might want to use it in your production environment.
So let’s start at the beginning with an understanding of what it does. Simply put, SCTV is a new formula that can calculate the tone value or dot percentage of any spot color ink. I know….I know….you’re probably wondering why another formula is needed when your current densitometer or spectrophotometer seems to already accomplish this task. However, there is an excellent reason why.
Legacy densitometers and pressroom spectrophotometers utilize Cyan, Magenta, or Yellow filters (or simulations of filters) to accurately determine the density of C, M, Y, and K inks. In addition, to determine dot area or tone values, they utilize a formula, usually Murray-Davies, designed around the measured C, M, Y, and K densities of tint patches. So far, everything works great as long as you are measuring C, M, Y, and K inks.
However, when you try to measure the density or tone value of a color which is not either C, M, Y, or K, this system breaks down and can no longer provide accurate densities and therefore accurate tone value measurements. This is because the Murray-Davies formula is only based on C, M, and Y filters and what you are now measuring is not C, M, Y, or K ink. For example, try measuring a green spot color and see what filter your instrument tries to use for the density calculation. Depending on the hue of your “green”, sometimes it will use the Cyan filter and other times it will use the Yellow filter. The problem is that the selection of this filter highly affects the resulting density values and therefore the resulting tone values as well. This unpredictable nature of measuring spot colors is a big problem and it makes it nearly impossible to properly set up tone curves when the measured values themselves are unpredictable.
So here comes the new SCTV formula. It is based on color measurements and not density values. Therefore, densitometers will never be able to calculate SCTV measurements and a spectrophotometer like the Techkon SpectroDens is required. Just like calculating tone values for C, M, Y, and K, color measurements of the substrate, solid, and tint patch are required for SCTV calculations. To make SCTV measurements, users just change the mode on their instrument and begin taking measurements the same way they always have.
So if you are interested in achieving accurate and consistent tone value measurements for any spot color, try using the SCTV setting on your pressroom spectrophotometer. This should allow you to create more visually linear tone curves for spot colors and vastly improve their predictability on press. Here at Techkon, we like to talk about “printing to the numbers”, reducing the “craft” associated with printing, and improving the repeatability of your manufacturing process. If you’re printing spot colors, SCTV is absolutely a great step forward towards that goal.