Suppose you want to create a dark and moody picture? Exposing to bias the histogram to the left will achieve this objective. This means dialling in minus values of exposure compensation. Want to go the other way and produce a light and bright picture?
Adjust the exposure compensation towards the plus values. You may need to swap metering methods because a multi-pattern metering mode will usually centre the tones on the horizontal axis of the graph, which averages them across the image brightness range.
This image, which has a brightness range of slightly less than five f-stops, produces a histogram in which all tones fall inside the horizontal axis.
Consequently, detail is recorded in both shadows and highlights. Arrows indicate the regions on the graph that correspond to the brightness levels on the histogram. An image with a very wide brightness range, shown with the histogram that plots the tonal range. Note that the graph spreads across the entire horizontal axis, rising at each end and clipping both shadows and highlights. It will also show you the effect of any exposure compensation adjustments you make. Some clipping can be acceptable in regions that should appear very bright, such as specular reflections on water or metal, white clouds, scenes in which the sun is included in the frame or when other bright sources of light are present.
Contrast is defined as the difference in brightness between light and dark areas in a scene. This is another factor that can be displayed in a histogram. Since the height of the graph represents the number of pixels in a specific tone, the histogram can show you whether the scene is contrasty or relatively flat, and where the peaks in contrast lie.
You can find out for yourself how the histogram reacts to exposure variances. Fill the frame with something of little variance in brightness - a white wall perhaps. Then take a series of shots at varying exposures to generate histogram spikes throught the entire range. You will find that a one-stop change in exposure will move the spike much further if it's near the center of the histogram and much less if it's near either end. Also, the base of the spike will be wider if it's near the center of the histogram.
Generally you should see a total dynamic range of at least 7 stops, again depending on your contrast setting. With the exception of seldom encountered situations like fireworks, cityscapes and moonlight scenes these 10 stops encompass every lighting situation you are ever likely to encounter.
Only on the ski slopes or at the beach will you need to stop down one more stop beyond Sunny 16 because of reflections off the snow and sand. If you read that again you'll find he is talking about the human eye and the brightness levels on this planet. He isn't suggesting a digital sensor has a 10 stop latitude, in fact the image further down the page shows about 6 stops. John Some cameras, some lenses, Various light sources.
My Flickr stuff. Approve the Cookies This website uses cookies to improve your user experience. By using this site, you agree to our use of cookies and our Privacy Policy. Register to forums Log in. Dec 16, 1. LIKES 0. Dec 16, 2. Actually I think neither view is strictly correct, although they each give some insight that is useful in general shooting, particularly when working with jpeg files for which in camera histograms are usually calibrated.
It surprises me that I cannot find any Mfg. Characteristic curves plot film density response to light for a wide range of intensities. It makes sense that each "cell" in digital sensors have some bottom threshold beyond which light is simply too dim to register, and some high threshold beyond which the sensor is producing the maximum signal engineered into it.
It also makes sense that, as the camera contains its own computer to convert these signals into a standard data format RAW or JPEG for transmission, there is no direct way for camera users to measure sensor signal strength. Complicating the picture for the user who would really like to know how his camera represents sensed light intensity in its data stream is the fact that the digital camera dynamically adjusts exposure to fit the conditions present when taking a picture.
Full manual mode requires the photographer to do the same thing for himself. This means that an enterprising photographer using a bit-busting hex data editor to discover the actual values for any pixel will not be able to figure out a true light level for the data he finds.
Even if there are light intensity values per pixel in JPEG, for example, it is not possible to know how bright a found x actually was in the original scene.
It is possible to remember what f-stop was used to make the picture, but keep in mind that exposure controls are used to adjust the light level camera sees to better fit its sensitivity. There are so many specific light intensities in nearly every well-exposed photograph that it is impossible to make generalizations from any measured pixel about the ability of the data to render f-stops.
An experimental approach to collecting this information would use a varible intensity light source in a plain setting, an independent method for measuring the light, and careful control of camera settings. A long series of exposures would be made with all the pixels in the picture registering as close to the same intensity as possible. You will have to be careful in the way you describe the results.
Each camera model might be engineered to have its own response to light. You would be able to state the exposure for the darkest pixels camera you used records and the exposure for the lightest pixels.
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