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Dynamic Range: Shadows and Highlights. Dynamic Range. 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.

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Presentation Transcript
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Dynamic Range:

Shadows and Highlights

Dynamic

Range

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.

When the photowell is full, a white value occurs. No photons after this are recorded, so all detail for these pixels are lost.

slide8

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

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Dynamic Range and Contrast

Low contrast | High Contrast

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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.

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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.

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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

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Low 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”.

High contrast

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Low 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”.

High contrast

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Crushed shadows

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Blown highlights

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Transformation: Pixel value x 10

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

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Real-world examples

Tools

Exposure adjustment

-Levels

-Curves

Better Tools

Selective shadow/highlight adjustment

High Dynamic Range (HDR) blending

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High Dynamic Range (HDR) Blending

Take two images which cover different exposure ranges

Blend together for greater dynamic range

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Important side effect

Raising shadows reveals noise!

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RAW Headroom

Original

JPEG -4EV adjustment in ACR

RAW format gives extra dynamic range headroom to restore crushed shadows and blown highlights

RAW -4EV adjustment in ACR

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Fill Flash

Shadows adjustment

Original

Fill flash

Low-power flash can “fill in” shadows

Better tones, less noise than shadows adjustment

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Shadows and Highlights

Dynamic

Range

Larger photowells allow a larger dynamic range to be captured

Larger sensors with less pixels => larger photowells