From art to print - color separation


On the screen printing floor, issues arise all the time that waste time and aggravate. But, for the most part, these issues are very hands-on in nature. You can see ink smudges and tape off pin holes. But before that stage a more abstract stage needs to be completed. This is the art design stage. Here problems aren't always as obvious and neither are their solutions. Traditionally, and often today also, art is designed from the ground up to respect the nature of screen printing. That is to say, the art designer designs the art from the bottom up to produce color separations. Often this is an easy task, especially when it comes to simpler jobs such as team names or logos. However, when it comes to the more complex jobs that require mixing of colors and using halftones to achieve realism and color accuracy, it can be hard to produce the artwork you had in mind. Unfortunately, compromises are often made. Screen print art designers are often very adept at working their graphics software just right to produce high quality output, but even these high levels of expertise and experience don't allow for a simple, direct conversion from one format -the art you want on a shirt- to another -the art you see on the shirt. As a matter of fact, it can take long hours of tweaking one design's color separations to get a near-perfect result. And even though the expertise at work is surely impressive and deserves recognition, it would be nice if such expertise could be put to work in the creative process of designing artwork, instead of the tedious and repetitive conversion process, which of course aims to reproduce the already finished creative product into one that can be printed using a less-than-perfect color system that changes its colors with every new print.

Selecting colors

One way to create the color separations from art is to simply "select" the colors. This approach produces films based on the closeness of an art color to an actual ink color. The closer it is, the darker it will appear on the film. This is the most used and most direct way to separate art into its constituent colors. It is, however, highly inaccurate, by its very nature.

One way to explain why color selection is inaccurate is to ask the question: How far is far? As stated above, we use less ink of a particular color at a particular place in the art if the color in the art is "far" or "very different" from the ink color. The problem starts with, how far is far? Well, we answer that by trying. Does it look good? Expertise is what gets you through this question. After many projects and lots of adjustments you get a feel for what range of colors to select. Also, to measure a distance between two colors, we can use different ways to measure. For one, colors can be represented in many different ways: red, green blue; hue, saturation, lightness; L, a, b; y,u,v; CMYK, etc. Normally, we use the RGB system to measure distances. But even within that system there can be discrepancies. Did you know for instance that the green channel translates to a lot more lightness than does the blue channel? Yet the distance usually measured between black and full blue is the same as the distance from black to full green. We aren't concerned about these details when selecting colors by range, we don't define exactly what "close" or "far" is and therefore the results cannot be consistent. That is to say, whatever the outcome of the separation process, there is probably a better way to do it, but we don't bother trying to find it since it's just too much work. We're satisfied with what we have and call it a day. We leave striving for perfection up to the real perfectionists.

Let's say we want to separate the following image. We'll be using 2 colors, blue and black.

Original art to separate

We select the blue using full range, adjust it to reach exactly across the range, all the way to black. The film looks like this:

Blue separation film

We do the same with the black:

Black separation film

So far, so good. This simple 2 color art seems to separate nicely. Let's print it. What order? Well, let's print the blue over the black:

Printing blue on black

As it turns out, something went wrong. The shadows aren't very black (on the left side). That is because they are transparent, which in turn is because they are partly blue and partly black. As a matter of fact, any areas that are part blue and black (a mix) are transparent, because neither the black nor the blue covers the area completely. Experienced screen print designers now want to yell out: "You can print a black full base and print the blue over top". And yes, you can. And that would solve the problem completely. But only in this special, very simple case. As a matter of fact, you could print a complete blue base with the black film shown above over top and you'd get the same result with the color separation quality being as good as possible. But, again, this requires in depth knowledge of the order of printing and how colors are formed. And, to top it off, again, it only works in this special case with only 2 colors. When adding more colors something will fall by the wayside and compromises have to be made!

Another way to explain why color selection is so inaccurate is to consider separating for instance using a very dark red ink, light red ink and black ink. Preferably, we'd like there to be a smooth transition between the black and the dark red, with no light red mixed in, and next a smooth transition between dark red and bright red. Unfortunately, when it comes to selecting the dark red, we have to use a range that reaches from the dark red all the way up to the light red, where the dark red fades to nothing. And the problem: the black is well within that range and therefore gets plenty of dark red. Again, we can counter this with expertise. We can split the image into two sections and process them separately. We could also simply print the black last and cover up the area where red is too much.

Say we want to separate the following image using 3 colors: Bright red, dark red and black. We use dark red because for some reason we want the color to be particularly well defined there.

Original art to separate

The dark red separation film after selection:

Dark red film

As mentioned above, on the far right of the dark red film we end up with an overdose of dark red. (The dark gray on the right side of the film should be white!) Really, color selection has failed us. We have to patch it up, use expertise and lengthy selections, image splitting and still we can end up with films that don't truly represent the original artwork, but with which we are nonetheless happy enough to print. In other words: a compromise.

Yet another problem encountered with color separation using selection of ranges of colors is that there is no defined printing order. Even though it matters which order you print in, whether for instance the black overlays the dark red, or the other way around, during the selection process this issue is not addressed, or not defined. Experience and expertise can partly make up for this but many issues arise that need dealing with. For instance, even though it may be easier to print black last during considering the color separation process, the actual printing process may prefer black being printed first for reasons of ink transparency etc. The different parts of the printing process may therefore dictate different printing orders and conflict arises. 

Index separations

To counter the inequity of color selection, some people opt instead for a different technique of separating their art. They use what is known as the index separation method. Index separations were never developed for screen printing and no one had inks in mind either during the development of this process. As a matter of fact, this method was developed to be able to display true-color images such as photos on displays that could handle only a very limited number of colors at once, known as the color palette. Software develops a palette or picks a preset palette and then mixes these colors together using dithering which is placing the different colors of the palette in different counts close together to form a mixed total which approaches the original image color in that spot as closely as possible. Most graphics software today can create these dithered images and therefore it is a very easy method to use. To separate out the films from these images, you can use the color selection method with a very short (0) range. The color accuracy is very high. That is to say: the methods used to dither images have been developed and improved upon for decades and produce high quality color matching. Unfortunately, there are again a few problems with this method when used in screen printing. For one, it isn't suitable for use with halftoning, which is really what we want. For two, there is again the problem of no screen printing order being defined or imposed. Really, an argument can be made for any order. The fact that we can't use halftoning is a real problem, because the screen printing process inherently does not allow for perfectly square tiny regions of ink on shirts to mimic pixels on a screen. However, the real big problem comes in when registration isn't perfect.

Say we index-separate the following art:

 Oroginal art to separate

We get two films, black:

Black film

And blue:

Blue film

And when printed perfectly, they make the following image:

Art printed perfectly

Which is pretty close to the original.

Unfortunately, we can sometimes print with not-quite-perfect registration. And if we are off by even 1 single pixel which in real life screen printing can be as little as 1/50th of an inch, we get the following result:

Prinmted art with only 1 pixel misregistration

And this is clearly not what we intended. Terrible. Note that this is not a problem at all when printing this particular job on a black shirt. Unfortunately this particular job is way too boring to print on any shirt.

We can, again, solve this problem by printing a black base with blue on top, or the other way around. Lucky for us, except that this stops working completely when we have art of 3 or more colors.

The automated approach

Who has time to figure out why this detail does this and such detail produces such quality improvement? Who has a decade to spend, learning expertise and getting experience? Progress doesn't mean knowing all there is to know. Progress is letting other people's knowledge work to our benefit. So we can forget about all the details mentioned above. It ought te be enough that we have acquired the expertise and experience to create stunning art or to produce exactly what a customer requests. Even though being able to perform all steps necessary to get from art to print is admirable, it is also tedious, repetitive and not part of the creative process. Creativity, of course, is what makes us different from machines and computers. As of the current state of technology, machines of any kind still have huge trouble producing original content. They are, however, getting better and better at performing tedious and repetitive tasks. They are human expertise and experience solidified into automatic processes. And as such, relieving us from the tedium, they enable us to be more creative. An artists dream!

So we try a product, a solidification of someone's expertise, to the best of their ability created to perform the tedious tasks as they themselves would. And when it comes to color separation, this means that automatic color separation software will often color separate the same way we would: Using color selection, or using the "index method". Well, for the record, if you're thinking of going the index-separation way, you probably already have what it takes to do this on your computer. You more than likely won't need any extra software to perform the small steps of selecting out the different films, which isn't hard and doesn't take long. So, that leaves us with software that automates the color selection process. As far as I know, all currently available software packages for automating color separation use an automated color selection process, save one. Correct me if I'm wrong. More on that one later.

Oroginal art to separate

A person knows which colors to select based on what he or she sees in the image. This image for instance would require a bright blue, and unless we're printing on black, a black ink. Automated separation software is not usually as smart. So it would be a good idea to leave the picking of colors up to a person. This is not usually the case. The software decides for you what colors you ought to use. And in the process usually decides that you need up to 9 colors (yes, 9!) to print your image. That, of course, borders on insanity. So then you read the manual which says you needn't print many of them. You can delete the ones with "little color" which it leaves up to you to decide what is little. Or you can "merge channels", which means something like: You can print 2 films on a single sheet. What rhyme or reason there is to this is not quite clear to me, but it is however clear that this can't possibly produce accurate prints. If you'd like a breakdown of this, comment on the article and I'd be happy to elaborate. Next we have to adjust things. Contrast of separate channels. Add channels for fleshtones. Make our oranges bright if there's a fire. Tweak. Use expertise. Use experience.

In the meantime, we're stuck with pricey software that produces a boat-load of films for our simple separation job. Better to do it by hand then. As a matter of fact, many designers have plainly given up on automated separation software in general because the results they got with them simply weren't up to par compared with what they could produce by hand. Expertise on the part of the expert won out over expertise of the software designers. Even trying such software is often experienced as a complete waste of time.

A better way

And now for the relief. Who said anything about having to select colors? Selecting colors produces a grayscale image, which we can then halftone. Wonderful, just what we need. Unfortunately, the color selection process isn't the most accurate. It isn't when done by hand, and it also isn't when done automatically. That's only because it cannot be accurate. The whole system is flawed. Index separations, however, are touted as the most accurate separations - color wise. Unfortunately, it's dithered and not halftoned. Which, as shown above, can make it hard to print. If only there were software that could produce grayscale images, or even halftones, that were separated with the separation quality of actual index separations. That would be great. But such as process doesn't exist, does it? Wrong. It does now.

Welcome to EZ Screen. Simply load your completed art, add whatever inks you decide are a good match or whatever inks the customer needs, including Pantone matches, select from predefined inks sets, or mix your own. Decide what order you would like to print in and have the films adjust accordingly. EZ Screen will mix correctly. It won't select colors, it will mix colors, exactly so as to produce the closest match. EZ Screen doesn't allow you to adjust anything, simply because there isn't anything to adjust. Merging channels makes no sense, because each channel is added by you, when you need it. Adjusting colors by range doesn't make sense, because all EZ Screen does is very high quality color matching to the art you already decided was what you wanted. There isn't a closer match possible using the inks you selected, so adjusting colors could only make the match worse! EZ Screen doesn't force some 9 colors on you, each of which may be as irrelevant to your art as the next. And EZ Screen shows you immediately what you'll get on fabric. It even has an on-fabric preview. EZ Screen allows you to use whatever fabric color as part of your art. EZ Screen is fast, the most accurate and complete. Really, all that is left to say is: Try it for yourself!

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