A histogram is a graph which shows the tonal range or brightness levels of a digital image. As you can see in the screen capture, the histogram (graph-top right) is bunched up at the right end. This means that more of the tonal values of the cute baby photo are closer to pure white. If however, the graph piled up at the left it would mean our photo had more shadows than highlights.
You’ve heard of megapixels with regard to camera capability. Megapixel means one million pixels. Digital camera resolution is measured in megapixels. One pixel (a picture element) while very small is still large enough to be registered and thus enhanced. Each pixel has three separate color channels (red, green, blue) which combine to produce a brand new color. Each color channel has a value from 0 to 255. Therefore 0,0,0, Black (r=0, g=0, b=0) has no value and 255, 255, 255 white (r=255, g=255, b=255) has complete value.
The height of the histogram indicates how many pixels are recorded at a given brightness level. I think of a histogram as “exposure by the numbers.” As professional photographers, we need to be very concerned when either end of the histogram shows a spike. This means we have no detail in either highlights or shadows and typically this situation is not optimal.
Our eyes are very sensitive and automatically recognize a properly exposed image. However, our cameras do not see the same way. The expert photographer has multiple tools which permit a proper exposure before, during, and after capture: hand held and in camera light meters, exposure compensation, continuous, strobe or ambient light, and of course, experience. All of this can become very complicated but in the end, we as the viewer know when an image seems correct and typically our instincts will be supported by the math. The primary aspects of concern with the histogram are the left and right edges. Any pixels that recorded as bright white (255) or as pure black (0), would be pushed up against the edge of the graph.
The “very cute baby” photo above was opened in Photoshop CS6 and color sample targets (1, 2, 3) were placed about and then analyzed. There are lots of numbers on the bottom right….however, the translation is simple and instinctive: each target has tonal values closer to pure white and the colors also seem balanced. One color channel does not predominate.This means I do not have to adjust and exposure in camera was spot on. Had I decided to adjust, the pair of numbers (for example #3 R: 241/241) would have shown a different value something like 241/237 but I wanted a tad more red in his facial skin.
For now, keep in mind how the baby’s eyes are in sharp focus and also represent the lightest and darkest points in the photo providing ultimate contrast and point of interest. I don’t believe in keeping an inadequate photo to “fix in post” and also would rather be safe than sorry so I spend the extra time on a few more exposures and know that one frame will always have perfect exposure, focus, composition and that final unmeasurable ingredient – expression.
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Even though a picture is worth more than 1,000 words….sometimes words will “tell the story”. My favorite blog is “Plant Talk” fromThe New York Botanical Gardens. Something to learn or something to see..daily. The posts which I enjoy the most continually provide something beautiful to look at and something new to learn. Looking forward to your comments.