Last time, in Part 1 of From Camera to Print: RGB & CYMK Color, we talked about the two main color spaces that photographers deal with when capturing and printing photographs. There we saw that RGB is for light-emitting devices like projectors and televisions and CYMK is for light-reflecting devices like posters and books. In this part, we're going to look at different printing processes and get some advice on which works best for photography.
The Printer's World
Photographers know the digital, or RGB, end of what goes into making color and the many variables that go into it. But there is another world of color that the printer battles with to reproduce it through various methods using ink. Using inks to represent what light can do is a huge challenge, especially when color accuracy is critical to the job.
Printers and presses are trying to match color with materials that cannot compete with what is coming out of computers and cameras. They can get close. Close enough to "fool" the human eye's perception, but materials and processes just simply cannot match the original.
The loss of color and detail fidelity to the original in printing is the same when we see an image, capture it, and then process it. Each step represents a loss of information. Therefore, each step "sees" less than the first.
A master printer said to me, "if your eye can see a gallon of color and your camera can only see a cup, then the printer can see just a thimble. That's what I've got to work with but still be convincing to the point that you don't see ink and dots."
Note the very small color range of the paper.
Printing Processes
There are a lot of ways something gets printed and the process used has an impact on the final product. Some processes are best for photographs while others work better for type or linear illustrations lacking smooth tonality. We'll skim through just a few of the most common processes:
- Letter Press
- Flexography
- Rotogravure
- Lithography
- Digital
Low-Quality Printing
The letter press is perhaps the oldest and simplest method of print reproduction for the masses. I say "for the masses" because it enabled a level of efficiency in printing unseen before in history. The famed Gutenberg Press was a letter press machine which is credited for kick-starting the age of printed books. This press allowed for literature, and therefore education, to spread throughout Europe and the world very rapidly. By the early 1800s, the letter press was responsible for printing everything from books to newspapers to flyers. Increased efficiency due to improved techniques and the steam engine allowed this to happen.
The Gutenberg Bible, printed on the Gutenberg Press. Photo by NYC Wanderer
Nowadays, the letter press is more of a specialty service because of it's low output compared to modern printing methods. You'll see this a lot in wedding invitations and a lot of low capacity jobs that aren't repeated very often. The papers are usually soft and the colors are very limited.
The letter press' lack of plate sophistication, low color capacity, and soft papers make it unsuitable for photography but better suited for ... well ... letters.
Another low-quality, but common, printing process is flexography. Basically, it's the printing method you see in rubber stamps. Instead of using a hard plate, like metal or wood, it uses a flexible plate to transfer the images onto non-porous surfaces. Food packaging, cardboard boxes, plastics, films, etc. It's advantage is that a wider variety of ink types can be used in order to print of the various surfaces. It's disadvantage is the lack of color complexity and jagged edges it produces. The jagged edges are the result of the pressing action as well as the flexibility of plate.
Office rubber stamps are a type of flexography. Photo by Julo
Medium-Quality Printing
I'm going to stick lithography into the middle because there are very fine examples of lithography, with good color and detail, but also poor examples with the colors all flat and blotty detail. In lithography, an image is etched into a plate, usually a flexible aluminum roller, and then coated with hydrophobic ink. Another roller is coated with water. The inked roller has the positive image while the water roller has the negative. So, the ink only sticks to the areas where the water isn't and the water cleans up the image.
This produces a higher quality print than the previously mentioned processes, but it suffers because the process itself and the papers used. Modern lithography uses an offset method where the image is transferred to the rollers, then to a rubber blanket, then to the paper. Depending on the paper used (usually absorbent),the precision of the presses themselves (plates, blankets, guides, etc.), and the inks, a widely varying range of color and detail can be achieved.
An example of lithography/offset printing is the newspaper. The paper, ink, and precision is low quality. Offset is best suited for huge runs at great speed that don't require much detail, usually because the majority of the job is letters. Newsprint has an extremely small color gamut, tonal range, and poor detail. So, "punchy" colors will be clipped, contrast will flatten, and fine detail will be mudded.
These presses are run at high speed as cheaply as possible. Sometimes the printed image is "out of register." Each of the four colors used in any image, Cyan, Magenta, Yellow and Black, has it's on specific plate. Sometimes this plates don't hit the paper exactly how the are supposed to resulting in a misaligned run. This is because no guides were used during feeding, allowing the paper to shift as it goes along the rollers. The resulting image can look like an old 3D image where the red and blue colors are positioned differently.
Modern lithography is one of the best friends of mass media. Photo by Sven Teschke
But hey, even with it's short-comings, lithography is much better than your office rubber stamp.
High-Quality Printing
Rotogravure is a high-quality form of printing commonly used in jobs that require extremely high resolution and many, many copies. This process is extremely expensive — as high as $60,000 per plate — due the high image fidelity and the ability to make literally millions of accurate hi-res reproductions. Who would use this kind of process? National Geographic would.
At it's height of popularity, National Geographic utilized the rotogravure process to accurately reproduce those amazing photographs they would receive from photographers around world. They needed a lot of copies that were sharp and rotogravure did that for them.
Unlike the letter press or flexography, the plates for rotogravure weren't raised, but etched. Tiny pits, or dots, were etched into the plate with acid. In it's infancy, plates were etched by hand. The depth and clustering of each pit determined the density of the color. So, a shallow pit would produce a light color while a deeper pit would be darker. Each plate had different etchings for each color. This meant that one press ran black, the next press ran cyan, and so on, just like newspapers.
The cylinder would roll through a fountain or pool of a single color of ink, flooding the pits, the flat surface would be squeegeed clean with a doctor blade, leaving only the pits with ink. The paper would then be fed between the etched roller and pressing roller. The process repeats itself for each color on a new roller.
The fewer image transfer steps of rotogravure contribute to it's high fidelity. Photo by Parktravelling
Perhaps the highest quality of printing are the various digital processes. This is mainly due to the close proximity to the digital original. They essentially take information directly from the file to the print without transfering it plates, rollers, blankets, etc. where each transeferrence of the information causes a loss in fidelity.
One example is the inkjet print, or "glicée" if you want to be fancy. It takes the digital information and directly squirts it onto the paper. High-quality printers and papers have multiple inks, usually 8 or more, to help with color and tonality as well as seriously small dots for detail. Photo inkjet printing has come a long way and is constantly improving. With high-end printers and papers, you can't tell the difference unless you "pixel peep". Some printers like the Epson 7900 Pro and even the 4900 Pro have passed the nose-to-the-paper test.
Another high quality digital print method is laser printing. It uses an electrostatic method much like a copier, but with colors and with a lot more accuracy. A laser etches the electrostatic roller which passes through the inks and onto the paper. Again, very few steps between the original and the print.
The most faithful to the original image, such as a photograph, is the digital photo print using lasers onto traditional photographic paper. This is the same method used in a traditional darkroom: light passes through film onto light-sensitive paper and developed with chemicals. Modern digital film printers use the digital image and project it onto the paper using lasers. The quality of the print such as color, tonality, and detail is dependent on the paper as well as the machine.
Paper, Ink, Finish
The paper's texture, materials, and color affect the final output. Photo by MichaelMaggs
Aside from the printing process/method, the paper and the ink used, the finish of the paper is another factor in printing. Cheap inks and papers, like those found in newsprint, produce low-quality imagery in terms of color, detail, and tonality. Low-quality inks and papers can cause colors to bleed, fade, smudge, or reproduce extremely inaccurate colors. So, going cheap at any point in the printing process isn't always a good idea.
A good experiement to do is compare a low-end photo paper to high-end photo paper. I've done it comparing common drugstore photolab paper, usually Kodak Royal, to a professional lab's standard paper, Kodak Supra Endura, using the same photograph. The color, detail, and tonality were obviously clear in a side-by-side.
There are a wide variety of papers for photographs that can affect the final outcome of the image. For example, canvas prints are fibrous and absorb lots of ink, sacrificing detail and contrast. Conventional photo inkjet prints and magazine pages have low absorbancies and hold the original color and detail better.
Another factor in printing is the finish of the paper itself. The finish of paper is actually a clay that is polished to different degrees for a different finish ranging from matte to glossy. The polished clay fills in and smooths the natural texture of the paper fibers and in turn increases reflectivity. As the surface becomes more polished and reflective, the images get sharper and gain contrast. The downside is that fingerprints, scratches, and indentations affect the image more easily and the glossiness of the surface can make it difficult to read/see.
The luster or pearl finishes are good choices because they offer a bit a both worlds. They have great contrast while not being distractingly shiny. They also are less prone to showing fingerprints and other smudges. I like my prints to be tangible but not ruined by normal handling.
Dot Patterns and Dot Gain
Now we get into the "pixel peeping" portion of printing. This part refers to the physical layout of the dots of ink used in printing. Nearly all modern printing processes use dots to make color and their gradients. There are two popular methods used to create these patterns, called a "halftone pattern". One is amplitude modulation and the other is frequency modulation. These terms might be familiar as they are the AM and FM of radio.
Amplitude modulation is when the ink dots are evenly spaced, but the dot sizes vary depending on the color and density desired. Want a very blue section? Lay down some large blue dots. Want a light pink? make those pink dots small. Want a yellowish-green? Lay down a larger yellow dot next to a smaller cyan dot.
Frequency modulation is when the dots are the same size, but their spacing changes. The pattern is more randomized and therefore produces smoother gradients because the lines aren't so straight. Need a deep red? Get those dots nice and crowded. Need a light gray? Space those black ink dots farther apart. Need a yellowish-green? Pack in more yellow dots in to the same space with a sprinkling of green dots.
Amplitude modulation (AM), shown, uses varying dot sizes and equal spacing to create color and tonality. Also, varying the angle of each pattern produces smoother gradations. However, AM screening is still susceptible to moiré; even with the angle changes. Photo by Pbroks13
Up close, like when viewed through a loupe, the patterns look like a mess. How could any of it look like an image of anything? But back up and it all comes together. Amplitude modulation is fine for the printed letter and photographs not requiring much detail, but suffers from moiré due to the neat rows. So, fine detail, like fabric will be lost.
Frequency modulation is much better for photographs because of it's lack of moiré and inherent ability to better represent smooth tonality.
The pseudo-randomized dots of frequency modulation prevent moiré because the pattern isn't a series of parallel lines. See moiré in the image above. Image by P. Fraundorf
Curious as to which printed piece uses which halftone pattern? Grab a loupe or magnifying glass and check out your newspapers, magazines, textbooks, and inkjet prints.
While you're "pixel peeping" those things, keep an eye out for dot gain. Dot gain is a process by which detail is lost and colors usually get darker and stronger. It's not just the ink dot growing due to the printing process, but it includes the whole thing: paper type, ink type, printing process, misalignment, process steps, and even drying. So, not only can the ink dot grow, but it can be misshaped, put into a slight different position, or change color. Dot gain is an approximation of divergance, usually a percentage, from the original image.
For example, a web press (offset printing) — used by newspapers — has a lot of dot gain because of the process: original to plate to rubber blanket to paper to dryer. That is 4 steps of separation from the original, and that is just the process alone. Factor in the paper type, ink type, drying method, alignment, etc. and the original ink dot has a lot to deal with before it's done. This is why measuring dot gain is an approximation.
High quality printing and materials usually have very low dot gains because they're usually fewer steps involved and the machinery/process is more precise. Therefore, the final product is more faithful to the original.
Next Time...
I hope you've gained an appreciation for the complexities that go into printing. In many ways it is like the complexities that go into photography. And in fact, both use a lot of the same tecnhinques to makes images and even use the same mathematical formulas to make their respective imagery. Cameras use pixels, printers use dots. Photography and printing have a lot in common. In my research and consultations for this article, I've gained additional appreciation for master printers and the level of color and detail they stuggle to reproduce.
In the third and final part of 'From Camera to Print,' I'll guide you through the process of optimizing your images for print and some equipment that can help you print more accurately. This will hopefully help you make versatile photographs that can live both online and in print.
