dynamic range: shadows and highlights

Dynamic Range:Shadows and Highlights

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

Red Green Blue

1 1 1

Red Green Blue

5 5 5

Not all “crushed shadows” are actually black

Red Green Blue

10 10 10

Red Green Blue

50 50 50

As long as pixels aren’t clipped to pure black (or white), detail still exists

Transformation: Pixel value x 10

Real-world examples

ToolsExposure adjustment-Levels-Curves

Better ToolsSelective shadow/highlight adjustmentHigh Dynamic Range (HDR) blending

High Dynamic Range (HDR) Blending

Take two images which cover different exposure rangesBlend together for greater dynamic range

Important side effectRaising 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 flashLow-power flash can “fill in” shadows

Better tones, less noise than shadows adjustment

Shadows and Highlights

Larger photowells allow a larger dynamic range to be captured

Larger sensors with less pixels => larger photowells

DynamicRange