Upload
wendy-parrish
View
216
Download
0
Tags:
Embed Size (px)
Citation preview
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.
DynamicDynamicRangeRange
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 FlashOriginalOriginal
Shadows adjustmentShadows adjustment
Fill flashFill flashLow-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
DynamicDynamicRangeRange