What is it that makes one picture more more striking than another? What is it that makes tones appear sharp and detailed in one area of the picture and smooth and transient in another? The answer to both of these questions involves the issues of color hue, color purity, and tone distribution. Image detail is determined by these three elements. We refer to this elemental package as HSL or hue, saturation, and luminosity.
These are the irreducible minimum elements involved in accurate color reproduction. While there are many more issues to be addressed in the processing of an image, these three are the make-or-break elements that must be understood and properly addressed if you want your color pictures to really deliver their message. And for best results they should be handled in that order; value, intensity, and tonality.
A PRIMER ON IMAGE DETAIL
Here’s why tone placement is my number one issue in image preparation; even more critical than color accuracy. Human eyesight has tonal perception and interpretation capabilities that far exceed the dynamic range of digital camera image sensors. Make no mistake, capturing seven stops of light range is an amazing feat. But capturing this wide range of tones doesn’t automatically translate into visual delineation, image definition, or effective tonal distribution.
Now that I’ve used all my “d” words, let me give you a down to earth explanation. Hang with me here because this will get a bit involved- but I think it’ll be worth your time.
First, let me defuse several three-dollar color-related words.
Chrominance and Luminance. Chroma refers to the color in an image while luma describes the non-color or tonal component. Achromatic is actually pretty easy to grasp. Remember your high school English… the prefix “a” means “without,” so a-chromatic literally means without color. In the HSL model of color, hue and saturation fall in the chrominance column while tonality and contrast are on the luminance column (the structural or tonal backbone of an image).
Where does “luminance” come from? Light is measured in lumens. A lumen is the smallest measurable unit of light emitting from a light source that is visible to the human eye. Luminosity then is the measurement of lumens emanating from a light source. The more lumens, the brighter the light. Light measurements are also made in increments called candelas. A candela is roughly the value of light produced by a single household candle.
Just as “horsepower” is a carryover index of the measurement of power… relating to the pulling strength of multiple horses… candelas is an index of the cumulative light emitted from multiple candles. These legacy terms are sometimes confusing.
I wish RGB color models were a cut and dried topic, but alas, the variables are legion. If you want more info about HSB, HSV, HSI models, go here. But be very careful as one can easily drown in the scientific minutia. I’m going to try to keep this on a basic digital imaging level that you can actually make use of today.
All colors are composed of three parts; value, intensity, and luminosity. Value (or hue) refers to the “color” of color, or what differentiates red from blue or green. Intensity (or saturation) refers to the purity color, and ranges from pastel to pungent (the more white light is combined with pure color, the more the color strength is diluted). Luminosity is the measure of the brightness of color, and relates to its lightness or darkness.
Detail in a digital image is another way of saying distinction. While hue, saturation and luminance all play a significant role in detailing an image, the heavy lifting is done by luminance. Remember our prior discussion (What Music Theory Taught Me About Digital Images), detail is the product of contrast, and contrast is almost completely controlled by the luminance element. Ironically, the most powerful tone control is not the luminance slider in the HSL panel, but rather the simple Levels dialog.
Shape the light. Contrast, like sound EQ cannot be shaped by a linear (bass-treble) type control. Such is the slider in the HSL panel; which simply lightens or darkens an image. I use a variety of controls to shape my tonal contrast, at the top of the short list is Levels and Curves. I’ll detail the list in an upcoming six-part series on the Histogram. I suggest you follow this blog NOW so you don’t miss this series.
PRACTICE BLATANT DISCRIMINATION!
Discrimination has gotten a bad rap recently. Discriminating is simply making a decision to act in one way instead of another. I discriminate every time I choose to one pair of socks over another! While cultural discrimination is bad behavior, in the case of color reproduction, discrimination is a very necessary thing. Without visual discrimination of tonal values, your lackluster image capture will just sit there looking blah. Result: mellow mush. Get in there and push some tones around. You’ll be surprised at what a difference a little visual authority can make.
Internal contrast is the real key to image clarity. Current image capture technology sometimes delivers a very limited visual range of tones. When it does you must learn to emphasize the tonal difference in critical areas of your photos if you wish to pass along the emotion that caused you to capture the image in the first place. You are an author, an artist, and a visual communicator. Take control!
Thanks for joining me. See you next time. Herb
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PS. if you have an iPad and are interested in learning more about the fundamentals of digital photography, I suggest that you take a look at my Accurate Color iBook in the iTunes Store