The Histogram
To properly "enhance" or "improve" a photograph, we need to start with the data the camera recorded.
Real Time Camera Histogram in Record Mode
Recorded Histogram in Display mode
When your camera does a meter reading, it is trying to determine what is mid-gray (18% gray) in the scene being recorded by the sensor.
If you plot horizontally the brightness/luminosity levels from dark (black) at the left (0) to brightest at the right (white - at 255), in 256 steps from black to white (8 bits) and plot in the vertical, the number of pixels at each step you get a graph called an histogram. Most cameras display or record histograms
"There is no such thing as a bad histogram." it is just a way to tell you how the light is distributed across the recorded photograph!
The Vertical Axis
shows the number of pixels
at each level (step) of brightness
The Horizontal axis has a scale of 0 - 255 (left to right) with 0 = black and 255 = white. Mid gray has a value of 128.
Almost all cameras can display the pictures histogram in playback mode, some show the histogram in "live" record mode. Though there is no such thing as a "good" or "bad" histogram, generally, a picture with an histogram that shows most of the pixels in the middle is better exposed than one that has the pixels clumped towards the black or white end of the graph.
A Normal Histogram
An histogram of an underexposed picture
An Histogram of an overexposed picture
With a little practice, you will be able to tell if your photo has good exposure values by looking at just its histogram.
So, what's the point? What do we need to really know here?
To process The "Perfect Picture" you need to know or determine:
- What pixels are white
- What pixels are mid-gray
- What pixels are black
- AND, You need to know the source of the light, The "WB"
The White Balance