What is a RIP? Why do I need to use a RIP? What is the RIP doing? Such questions are found floating in the heads of prepress personnel throughout the entire graphics industry. We will address these issues to clear up some of the foggy areas of image handling and graphics processing.
First of all, the basics; a RIP is a Raster Image Processor. We can start by breaking apart this acronym into its components and then bringing it all back together. Raster is a collection of picture elements, or pixels, that when arranged in a very specific sequence create a picture. Raster is the opposite of vector. Vector is resolution-independent, it is mathematically drawn based on geometrical formulas. Modern-day RIPs can handle both raster and vector image formats, however the classical definition of a RIP implies the use of raster graphics. The second word is image, which presumably most everyone is familiar with. An image can be a photo, a gradient, or even a picture of text. Processing is a generic term that simply implies that there is some sort of change being made. All together Raster Image Processors use mathematics to convert varying files into pixel based output images.
In the printing industry a RIP is typically a standalone program that performs high fidelity and high-resolution image conversions for high-end output devices. It is only natural that when the cost of an output device such as a platemaker, proofer, or imagesetter is taken into account, more care is put into the handling of the files being passed through the system. When the cost per mistake climbs up, the importance of error free ripping rises too.
That should give you some insight into what the RIP is doing at a fundamental level, but what about the specific things that happen while a given file is being ripped? What are things like flattening, trapping, imposing, compensating, embedding, and colorspaces? This is where things can get complicated, in most situations when a RIP is installed, a certified technician will create templates for you. However, at times it is best to be self-sufficient and it is important to know what is happening behind the scenes so that in the heat of the moment, if there’s a problem then you can fix it.
Flattening is a step in the RIP that has undergone some major changes in the last few years. With the advent of more advanced prepress software like Adobe’s Creative Suite 4 and Quark 8, files are being passed to the RIP with many more degrees of transparency, or alpha, and objects with different opacities on top of one another. These areas of mixed color have long been a sore spot with graphic designers. Color variations that crop up at the very end of the output process can give designers who plan for one color and end up with something different quite a headache. Modern RIPs use standard formulas for handling transparency and flattening which offers greater stability to a workflow. This is a common reason to update your RIP.
Onto trapping, trapping is a feature that makes it far easier for a printing press operator to produce quality work that is appealing to the eye. Subtle misalignments in color on a printing press can leave gaps of white paper showing where two or more colors butt up to each other. As a general rule of trapping, the lightest of the colors in question will grow to overlap the darker colors. This helps to keep this process from altering the final look of the artwork while simultaneously making the job easier to work with. The two key words when talking about trapping are choke and spread. The two words are opposites, choke referring to a color shrinking to induce overlap. Spread refers to an area of color growing outward to become slightly oversized. Trapping has become increasingly incorporated into end-user software packages like InDesign or Quark but most RIPs have trapping modules that can be turned on to perform this task automatically every time a job is ripped.
Imposing is a term used when creating a booklet. Because books have a specific order for the pages and each page often has a front and a back, booklets are typically printed out of order and then assembled later for efficiency. Imposing is the process of breaking a booklet up into its components and arranging the pieces so they can be printed easily.
Imposition can be pretty tricky to accomplish and it is not uncommon to see people folding up dummy booklets to help them figure out how to lay out a job for a press. Modern RIPs and Workflows are the magic wand for imposition. It is now as easy as telling the software how many pages your book has, how it is going to be bound, and a few other odds and ends enabling the RIP to do the work for you. Software controlled imposition greatly reduces errors in booklet production. The repercussions of a mistake in imposition can be pretty grim because only one out of place page can screw up the sequence of an entire book and easily cause a job to have to be started again from scratch.
Dot gain compensation is something most RIPs do automatically. Dot gain is a term used to describe the way a droplet of ink spreads out as it’s soaked into paper. The darkness or brightness of a color is controlled in printing by altering the dot percentage, which is a measure of the percentage of ink area vs. blank area. When an ink spot spreads out it can throw off the dot percentage and darken a printed color. Fortunately this is a well-known caveat of the process of printing and by means of dot gain compensation graphic artists and RIPs can retain very tight control of the final look of a printed piece. A RIP will look at the color a graphic artist intends a specific element to be and will reduce the dot percentage by the dot gain of the output device to achieve an ideal dot percentage to use to get the intended result. Dot gain for printing presses is typically around 20%. In color critical situations output devices are very accurately measured and this information is entered into the RIP to produce perfect color.
Embedding fonts is crucial in print production. The choice of what font to use is one that is often labored over by a graphic designer, the look and feel of text can have a great influence on the feeling or mood set by the words that are written. For this reason, it’s absolutely necessary that the font chosen by the designer be passed through the RIP with the file so the look of the piece is maintained. The Adobe PDF standard encompasses a robust mechanism for embedding fonts or subsets of fonts into a single file that can be easily passed around or delivered to a printer. RIPs check for fonts used in a job to be embedded. If the font is not present a job will be rejected. Modern workflows watch closely for this because it can slow down production if someone has to go track down a font.
Colorspaces are another thing that RIPs have to keep control of. The two main colorspaces are RGB (Red, Green and Blue) and CMYK (Cyan, Magenta, Yellow, and Key/Black). CMYK and RGB are polar opposites. CMYK is a subtractive color model where as you add pigments or dyes your final mixed color becomes darker. Subtractive color models are always used in printing where we’re starting with ink or dye. RGB is an additive color model where we are mixing light to create color. Mixing light is how your computer monitor and television create color.
Colorspaces matter when it comes time to rip a file. A picture in the RGB colorspace will not come properly when passed through a CMYK RIP. A RIP has to identify elements that are the wrong colorspace and either convert them on the fly or bounce the job so the artist can fix them.
Transparency flattening, trapping, imposition, dot gain compensation, font embedding, and colorspace conversion are all jobs your RIP has to do whenever it processes a file. These steps are all important when trying to run a smooth operation and process a large number of files in a timely manner. A trade professional has done each of these steps manually for decades but with the advent of the computer and the evolution of hardware and software these once complicated tasks can now be done in the blink of an eye. As prepress software evolves, RIPs must evolve as well. I hope this helps your understanding of some of the complex processes that often go unnoticed or are simply unknown.