When the photowell is full, a white value occurs. No photons after this are recorded, so all detail for these pixels are lost. If the electron count is below a certain threshold, it is just recorded as black. So if there aren’t enough photons, all the detail in those pixels is lost. DynamicRange

Large dynamic range: very bright and very dark areas in same scene

The camera has a limited dynamic range. Thus it can only capture a certain portion of the total dynamic range of the scene.

Dynamic Range and Contrast Low contrast | High Contrast

Histogram: plots pixels according to brightness: L-R, Dark-Bright Low contrast: Most pixels in middle, few very dark (shadows) or very bright (highlights) areas. Result: Flat, boring picture. No defining characteristics.

Histogram: plots pixels according to brightness: L-R, Dark-Bright High contrast: More pixels toward edge, in very dark (shadows) or very bright (highlights) areas. Result: Interesting, dynamic picture. Sharply defined characteristics.

Histogram: plots pixels according to brightness: L-R, Dark-Bright Low contrast: Most pixels in middle, few very dark (shadows) or very bright (highlights) areas. Result: Flat, boring picture. No defining characteristics. However, low contrast can always be edited into a high contrast image

Low contrast High contrast High contrast has caused this area to be completely white, destroying all detail. It is impossible to get this detail back – this is known as a “blown highlight”.

Low contrast High contrast High contrast has caused this area to be completely black, destroying all detail. It is impossible to get this detail back – this is known as a “crushed shadow”.

? Crushed shadows

? Blown highlights

RedGreenBlue 111 RedGreenBlue 555 Not all “crushed shadows” are actually black

RedGreenBlue 10 RedGreenBlue 50 As long as pixels aren’t clipped to pure black (or white), detail still exists Transformation: Pixel value x 10

Real-world examples Tools Exposure adjustment -Levels -Curves Better Tools Selective shadow/highlight adjustment High Dynamic Range (HDR) blending

High Dynamic Range (HDR) Blending Take two images which cover different exposure ranges Blend together for greater dynamic range

Important side effect Raising shadows reveals noise!

RAW Headroom Original JPEG -4EV adjustment in ACR RAW -4EV adjustment in ACR RAW format gives extra dynamic range headroom to restore crushed shadows and blown highlights

Fill FlashOriginal Shadows adjustment Fill flash Low-power flash can “fill in” shadows Better tones, less noise than shadows adjustment

Larger photowells allow a larger dynamic range to be captured Larger sensors with less pixels => larger photowells DynamicRange