Getting Good Color
"I want the best reproduction I can get. The color has to be perfect."
We wish there were some magical button we could push or knob we could set to "perfect" to satisfy this simple request by our customers, scanner operators, pressmen, and sales staff. Unfortunately color is a complex and subjective experience that cannot be addressed so easily and quite often, not to an ultimate satisfaction.
We would like to say in advance that everything mentioned on this page is a gross underestimation of the complexity of color, getting good color, and color theory itself. Volumes have been written by color theorists and scientists about the origin and perception of color that cover the topic in far greater detail than we hope to on this site. For the sake of brevity, we've listed the major concerns that we -
and you - should think about when trying to reproduce that perfect image, and the processes we use to try and obtain it.
Two vital "colour bibles" used by our scanning and color department are:
Perception of Color
Origin of the Image
Capture of the Image
Perception of Color
The human perception of color is a subjective
process. This means that everyone "sees" color differently. Get a group of people together, have them look at a particular shade of green, and ask them if the color looks like it has more blue or more yellow content in it. This could very easily keep that group in
debate for a very long time!
The light an object is viewed in also adds a subjectivness to the perception of a given color. Fluorescent lighting will accentuate the blue and green spectrums of any given subject, while incandescent lighting will make the same subject appear warm or reddish. Can we guarantee that our end user will view the product under
the same 5000K balanced light we use to tweak the color to the nth detail? We wish.
Another aspect of subjectivness is the social and cultural influence of what a color is "supposed" to look like. It is a common knowledge in the publishing industry that you can tell if a particular model was photographed by an East coast or West coast agency. If the flesh tones are pale and translucent, it's an East coast agency. If the skin tones are tan or bronze, it's West coast. This is an example of how social subjectivity affects what we consider to be the "correct" color for a particular subject. So now, in addition to being color scientists, we also have to be color sociologists. Great.
Add to all this the fact that not a single scientist or theorist- and it is a fact- truly understands
how humans perceive color. Theories upon theories abound, many of them convincing enough to almost
be fact, but in reality, they are all still theories.
So where does that leave us, trying to obtain the "perfect" color when we cannot even understand what it is or how it's going to be seen by any given user? We can only assess our final product- the printed piece- in terms of the raw materials on which it will reproduce: commercial printing paper and the colored pigments in our inks. We must set all subjectivity and neurotic concerns aside, for this
is our ultimate reality. With this pretext in mind, we assess and aspire to the perfect reproduction of an image using four basic standards: printability
, nature of the original image
, methods of capturing
that image, and optimal use of the color spaces
The commercial world of full color printing has perhaps the most limited palette of all. We have four inks, cyan, magenta, yellow, and black, with which to reproduce the world's color with unerring accuracy. Is this even possible?
- Tone: The tonal range visible by the human eye is much wider than possible with printing. Even in the blackest black of a transparency, a logorhythmic density of 3.0 to 4.0 is average, yet the blackest black we can print with inks is about 1.80.
- Color: Original artwork that contains flourescent inks or
other colors outside the CMYK gamut (see color spaces, below) simply cannot be reproduced in CMYK.
So how can it be done? The "trick", if there is one, lies in using the things we know about color and contrast to our advantage to "fool" the eye into a perception of sameness. By increasing the contrast of an image (lightening a 3/4 tone next to a black, for example) we can fool the eye into believing that the
black actually is darker than a 1.80 density -- and appears the same as the original. The same is true of color. To make a red appear more red, we can make any adjacent neutrals or colors slightly green or cool, thus using the concept of simultaneous contrast to enhance the color.
For the methods and standards by which we determine printability and the closest possible color of a subject, see the final section of this page, procedures
Origin of the Image
We are all familiar with the term, "Garbage In, Garbage Out." When printing high resolution images to film, the final product is only going to be as good as the original or the scan that captures it. When determining the printability of an original:
Capture of the Image
- Grain: at arm's length, a photograph or a transparency may appear smooth with no apparent grain problems at all. View the original with a loupe (magnifying device) and look for areas of graininess. These will increase noticeably the more the image is enlarged. When planning to use images for enlargement above 300%, try to use originals in a 4" X 5" transparency or 8" X 10" print format. Grain will be much easier to control.
- Contrast: Although an original image may look better in a contrasty version, this actually decreases the tones available to reproduce. When the choice is available, select a less contrasty, "flat" version. The contrast will return when the shadow areas are placed at the darkest printable dot possible, and any intermediate tones will be maintained.
- Color: Obviously the closest color possible is always
desired in an original, but keep in mind that the colors you see in transparency dyes may not be replicable in CMYK. The cleaner the colors are in the original, the more likely it will be that we can maintain the color integrity in reproduction.
Be especially wary of original artwork. Many pigments used in original art
may not convert to CMYK as efficiently as expected. The worst case of this is when white titanium or lead pigment is used to create whites in artwork. Often this is seen by the scanner as a light blue due to the phenomenon known as fluorescence. When in doubt, have the work photographed to test the integrity of the color. If it holds fairly well in the photograph or transparency, it should hold in scanning the original. If it does not, you will have the transparency to scan instead of the original, as well as having something you can send to other scanning companies while keeping your original safe in its frame.
The descending price and increasing capabilities of home scanners and digital cameras have prompted many end users to attempt to capture their own images with these devices. While we agree that CCD (Changed Coupled Device) technology has come a long way, there is still no comparison to a high-end drum scan, with the exception of a quality digital camera back.
- Tonal Range: Drum scanners use PMT
(Photo-multiplier Tubes) to capture and amplify subtle differences in tonal changes of images. In addition, most scanners maintain dedicated computer boards for converting these analog signals into more accurate CMYK values. The result is higher detail, more accurate color, and an overall sharper image.
Lower-end scanners, on the other hand, use CCD (Charged-Coupled Device) technologies to capture imagery. The problem with this technology is that as the actual light reflected to the CCD decreases- in darker and shadow areas - the digital CCD does not always sense the subtle differences in tone in the original. Not only does it not have a way to amplify the signal, it relies on a preset table of values to produce image pixels. The result is a streaky, nondescript "fill-in" of the shadow areas of the image.
- Registration: In a high-end drum scanner, each
scanning line captures all color values in an image in a single pass, eliminating registration issues that occur with multi-pass scanners. CCD scanners usually make their RGB composites by scanning in three passes with a red, blue, and green filter to separate out the image color. Often these passes don't line up exactly and
a mis-registration can be observed in the highlights.
- Overall Sharpness: Drum scanners use highly refined, microscopic optics to capture images, whereas CCD's use little or no optics at all. Again, the result is a higher image integrity and overall sharpness without manipulation in Photoshop.
The bottom line here is that if you want the best, you have to start with the best and continue that pursuit of excellence throughout the process, from original to capture to film to the final printing.
Various approaches to how humans perceive color all address the issue by discussion of color space or color gamut. This is basically defined as the range of obtainable color using a particular pigment or color source. While there are many color space methods and theories in existence, we are only going to discuss two here: the RGB and CMYK color spaces, as those are the two most directly used in offset reproduction.
The RGB color space is the range of colors generated by colored light. On a computer monitor, various brightness' of red, green, and blue light are generated from zero (no light at all) to 255 (light at its fullest intensity.) A white background, therefore, would be represented by the brightness of red, green, and
blue light all sent to the monitor screen at their fullest intensity - 255, 255, 255. A black screen is all lights off - 0, 0, 0.
Key to understanding the problem between RGB and CMYK is understanding the fact that all RGB colors are generated from the three primaries of red, green, and blue light, while all CMYK colors are generated from the primaries of cyan, magenta, yellow, and black for additional contrast.
Where is yellow in the RGB color space? Is not yellow considered a primary color? Not in the RGB space.
You have to mix red and green light to get yellow, considered a secondary color in RGB. The RGB color space is thus considered an additive
process, as opposed to the subtractive process of reflected pigments discussed below.
The CMYK color space is a theoretical "opposite" to the RGB color space and is more akin to the color space most of us are familiar with. It's primary colors are cyan (blue), magenta (a bluish-red), and yellow, with black to add contrast where the impurities of the other three colors prevent a pure black from
forming when all three colors are mixed. It is considered to be a subtractive
> color space. As opposite primaries are added to each other, each color actually subtracts the amount of light reflecting from the mixed surface.
So how in the world can we get from one to the other with any accuracy? How can we get the bright RGB blue to print as we see it on our monitor?
The answer is . . . you can't. You can't mix a subtractive pigment to get the same color generated by light. It simply cannot be done. The best that can be done is to maintain the most vivid blue possible using cyan and magenta. While there are many colors that can be found as equivalents in both color spaces, there are
many that do not. The only solution is to "fool the eye" by adjusting adjacent colors to mimic a simulation through simultaneous contrast.
The mechanics of everything mentioned above become very important when we consider these restrictions. A scanner reads an image in RGB. For the RGB values of each pixel of the image, a CMYK equivalent- or it's closest possible approximation- is returned from a color lookup table. The accuracy of this conversion is only going to be as close as is physically possible between the two color gamut's. Also the larger and more detailed the CLUT, the more accurate the color conversion is likely to be. This is why the color from a drum scanner will always be superior over an RGB image converted in Photoshop. It has computer boards dedicated to making this RGB to CMYK conversion that are so large they demand the entire attention of the computer's CPU. There are other RGB to CMYK programs that boast of superior conversion abilities, but the better they get, the slower they run, due to the mass amount of data required to make the conversion to CMYK.
You may have skipped this entire page and simply jumped to this link from the top of the page. If you have, the numbers and procedures we mention below are really going to do you very little good. If you simply follow the steps below with no knowledge of the concepts mentioned above, you are likely to do more damage than good when attempting to get the most out of your image. We recommend a hot cup of tea or coffee, return to the top of the page, and telling your boss you're doing some intensive R & D. Or you could just read on and cross your fingers.
Below is an outline of the most general form on what we do to get the best scan possible. We cannot emphasize enough that this is a general
outline, as each original and its reproduction poses its own unique challenges and problems.
- Scanner Setup
- Assess Image
- Assess Requirements
- Assess Scanned Image
- White Point/Black Point
- Color: Reference Real-World Equivalents
- Overall Final Assessment
- Test Proofing
- Assess and Adjust
- Quality Control: Proof vs. Press