The Dynamic range of an image is the range of tones between the brightest highlight and the darkest shadow. It is sometimes referred to as the contrast range but dynamic range is a more accurate and appropriate description. The dynamic range of a scene is the number of stops between the brightest highlight and the darkest shadow and therefore the dynamic range of a camera is the number of stops it can capture in a single frame. If a camera’s range is lower than that of the scene, detail is lost in clipped shadows and highlights, however if it is greater than the scene, no detail is lost and the image produced won’t contain any clipped highlights or shadows if exposed correctly.
Camera Dynamic Range
To roughly test the dynamic range of my camera I will shoot a scene containing both bright highlights and dark shadows and calculate the range between them in f stops. To do this, first I needed to wait for a sunny day and find an appropriate scene. Luckily I didn’t have to wait long, I decided to use the bright white door of our garage as the main highlight of my shot. A shaded area under a bush in the background provided an adequate area dark shadow.
I set my camera at ISO 100 to minimise the possibility of noise and chose an aperture of f/8 to keep the entire scene in focus. I also used the evaluative metering mode so that the my camera would tell me when the scene was correctly exposed. Before taking the shot, I made sure that there was as little highlight clipping on the door as possible. I couldn’t under expose too much as I would’ve lost a lot of detail in the dark areas.
1/160 sec
The shutter speeds written on the image indicate what it would’ve taken to correctly expose these individual areas. In order to find these shutter speeds I changed my camera’s metering mode to “spot” and zoomed into each area using my 200mm telephoto lens. I also took photographs of each image as I recorded the shutter speeds, these can be seen in the gallery below. I didn’t use a tripod so in the shots of the darker areas with slowest shutter speeds, there’s a quite a lot of camera shake blur.
Using Photoshop’s pixel value sampler I can see that the majority of the door’s tonal values are between 240 and 247; this is obviously right at the brightest end of the scale which runs from 0 (black) to 255 (white), any brighter and the area would have been highlight clipped. To find the darkest area that still contains detail I moved to the shadows at 100% magnification and increased the exposure by 2 stops so that the detail was visible. The image below shows the shaded area under the bushes clearly has a lot of noise now that I have increased the exposure.
The darkest pixels I can find that contain actually detail and aren’t “just noise” have values between 15 and 30 with the red channel having the highest and blue the lowest values in each area I test. The values drop to between 5 and 18 when I undo the extra exposure, telling me that the detail I see is in fact detail because if the values were now below 0 then what I saw a moment ago will have just been noise as detail can not just appear out of pure black. It is blatantly apparent that photographs contain much more noise in dark areas and therefore to retain as much detail as possible it is best to over expose these areas and then darken later using image manipulation software such as photoshop. However, overexposing an image with very bright areas will result in highlight clipping and so should be avoided. Slightly underexposing a shot of a bright scene and then increasing it’s exposure later is also something to think about. If a scene has a higher dynamic range than that of the camera, a tripod can be used to capture multiple versions of the shot, each at a different exposure and these can be merged together during post processing to create an image of maximum detail with a higher dynamic range than previously possible by a single shot alone.
Dynamic Range in stops
I have also calculated the dynamic range of my shot in stops. If the darkest area (containing visible detail) needed to be shot at 1/10 sec and the brightest at 1/1600 in order to correctly expose them and my camera was able to capture these areas in a single shot (without shadow or highlight clipping) it means that my camera’s dynamic range is at least 7 stops, if not 8. This seems to approximately comply with the findings of other people for my model of camera (Canon EOS 500D) but I have read claims of a range up to 11 stops.
Scene Dynamic Range
In this section of the post I shall explore study a variety of different scene to find their Dynamic Ranges in stops using the same technique as above.
High Dynamic Range
ISO 200 f/5.6 1/100s
Bright Area (Top of Hedge) – ISO 200 f/5.6 1/2000s
Dark Area (Shaded area of tree in foreground) – ISO 200 f/5.6 1/8s
Range in stops – 8 stops
Average Dynamic Range
ISO 200 f/9 1/640s
Bright Area (Flower) – ISO 200 f/9 1/1250s
Dark Area (Moss in background) – ISO 200 f/9 1/13s
Range in stops – Approximately 6 and a half stops
Low Dynamic Range
ISO 200 f/9 1/320s
Bright Area (Bottom Right Slab) – ISO 200 f/9 1/400s
Dark Area (Crack in middle between slabs) – ISO 200 f/9 1/30s
Range in stops – Approximately 4 stops
At a glance this scene appears quite flat thus one would assume it has a low dynamic range, however I would consider a range of 4 stops to be quite average and when viewing the histogram the values are spread quite far across the tonal scale therefore giving it an average range.
Average Dynamic Range (2)
ISO 200 f/9 1/80s
A lot of the sky has been clipped in this shot but there are parts where it’s blue colour is still slightly visible.
Bright Area (Sky in background) – ISO 200 f/9 1/2000s
Dark Area (Leaves at top of image) – ISO 200 f/9 1/60s
Range in stops – Approximately 5 stops
Low Dynamic Range (2)
ISO 200 f/8 1/1000s
Bright Area (Whitest Cloud) – ISO 200 f/8 1/2000s
Dark Area (Grey Cloud) – ISO 200 f/8 1/500s
Range in stops – 2 stops
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