Introduction to Understanding Your Digital Camera’s Histogram By Tibor Vari

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# Introduction to Understanding Your Digital Camera’s Histogram By Tibor Vari - PowerPoint PPT Presentation

Introduction to Understanding Your Digital Camera’s Histogram By Tibor Vari Agenda Digital/Film Basics Color by Numbers Dynamic Range So What is a Histogram? Samples Myths Summary Sources Digital/Film Basics A Digital Sensor is similar to film in that

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Presentation Transcript

Agenda

### Digital/Film BasicsColor by NumbersDynamic RangeSo What is a Histogram?SamplesMythsSummarySources

Digital/Film Basics
• A Digital Sensor is similar to film in that
• You can overexpose an image (blown highlights)
• You can underexpose an image (too dark)
• The meter will expose for 18% gray
• Dynamic range is about 5 F-Stops for digital (about the same as slide film)
• Digital stores color information as numbers
Color by the Numbers
• A Pixel = 3 “buckets” Red, Green, & Blue
• Each color bucket ranges from 0-255
• White 255,255,255
• Black 0,0,0
• Red 255,0,0
• Green 0,255,0
• Blue 0,0,255
• Magenta 255,0,255
• Cyan 0,255,255
• Yellow 255,255,0

Total color combinations = 256*256*256 = 16,777,216!

Tonality

• +2 ½ stops: textureless white Broad expanse of snow (overcast)
• +2 stops: extremely light Textured snow, sand dune
• +1 ½ stops: light light Birch bark
• +1 stop: light Khaki shirt
• + ½ stop: dark light Caucasian skin in sun
• Metered value: medium tone Most grass, green leaves
• -½ stop: light dark Caucasian skin in shadow
• -1 stop: dark Animals with dark hide
• -1 ½ stops: dark dark Dark Shadows with texture (pine tree bark)
• -2 stops: extremely dark Fur on a black cat
• -2 ½ stops: detailless black Night sky
• Sunny 16 Rule Daylight exposure = 1/ISO second at F16
• Camera meter wants to make everything 18% gray
• Snow or Beach Scenes - Compensate by +1 to +2 F-Stops
• Dark subjects like a black cat - Compensate by -1 to -2 F-Stops

3 Way Tug of War

Shutter Speeds

1/1000 1/500 1/250 1/125 1/60 1/30 1/15 1/8 ¼ ½ 1” 2” 4” 8” 15” 30”

Freeze Action <-Silky Water-> Low Light

Lots of sunlight F11-F22

Wide Open Apertures Slow Film (ISO 50)

Fast Film (ISO 400+) Narrow Apertures

F Stops

F1.4 2.8 4 5.6 8 11 16 22 32

Portraits Landscapes

Shallow DOF Great DOF

Background blurred Everything sharp

ISO

(film/digital speed – generally in 1/3 to ½ stops)

50 100 200 400 800 1600 3200

So What is a Histogram?
• A Digital camera histogram is a graphical representation of the brightness levels (from pure black to pure white), in an scene and the relative count of pixels within each brightness level.

40 colored tiles represented by the histogram

Where the shadows, midtones and highlights fall within the histogram

http://www.dpreview.com/learn/?/key=histogram By Vincent Bockaert

Pixel sensor collects light while shutter is open

Digital Histogram on a D2x

Digital Camera monitors are not calibrated! Thus you cannot judge exposure or colors by it!

Use your histogram to determine image exposure! If you do, you will not have to look at the image using the camera monitor at all!

Finally, your monitor will be difficult to see in daylight – the histogram will in fact be easier to see

Sample Image

This image is well exposed though a bit flat.

The black shadow and white highlights are virtually nil.

Note: Taken from http://www.sphoto.com/techinfo/histograms/histograms2.htm by Steve Hoffman

Sample Image

Mid-tone

118 R

124 G

136 B

24 R

23 G

18 B

Highlights

238 R

232 G

220 B

Pixel count high for sky

Sample Image

R249

G186

B89

R144

G160

B175

R16, G13, B12

Sample Image

R67

G60

B54

R2

G2

B2

R255

G213

B171

• Workarounds:
• use balanced fill flash on the foreground
• use a graduated neutral density filter
• take multiple exposures and merge them digitally
• go home

Images & text from http://www.nikonians.org/html/resources/guides/digital/histogram_101/index.html by Digital Darrell

Exposed for foreground

Blown Highlights

White Pixel count

Merged in Photoshop

Exposed for mountain

Black Pixel count

http://www.dpreview.com/learn/?/key=histogram By Vincent Bockaert

(High Key sample)

There really isn't just one proper histogram for any given image. You can shift the tonal range (the histogram) around to lighten, darken or adjust the contrast in an image. To take advantage of the information supplied by an image's histogram you have to be able to visually interpret the image content, taking into consideration the location and approximate percentage of highlight, shadow and midtone pixels in the image itself. Because of the snow, you would expect this image to have a majority of its pixels to the right side.

(Low Key Sample)

A majority of the pixels are to the left of the center of the graph.

ISO 800

F16

.2s (1/5)

+.5 comp

A Mode

Note:

Highlightsclipped,

No software can recover details from clipped shadows or highlights

ISO 800

F16

.2s (1/5)

A Mode

ISO 200

F16

.8s

A Mode

ISO 200

F8

.2s

A Mode

Tough Images

Whites not clipped so detail is retained

Note: Image from http://www.naturescapes.net/092004/gd0904.htm by Greg Downing

A Couple of Myths
• A perfect histogram is a camel back!
• Better to underexpose – you can always bring it back up in Photoshop!
Summary
• Watch for blown shadows and/or highlights – if you have them, make exposure adjustments or use ND filters. Use the “blinkies” if your camera has them
• Use the histogram and not your camera monitor to judge if your image is properly exposed
• Instant feedback in the field if you got the shot! No waiting two weeks for the slides to return!
• Interpret your histogram based on the scene.
• Try keeping the histogram to the right but at the same time not clipping the whites (interpret it)
Sources

Below are some websites that I used for research.

Please note that I made liberal use of some of their images to use as examples in this discussion.

• http://porg.4t.com/Histogram.html
• http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml
• http://www.sphoto.com/techinfo/histograms/histograms.htm
• http://electronics.howstuffworks.com/digital-camera.htm
• http://www.nikonians.org/html/resources/guides/digital/histogram_101/index.html
• http://www.naturescapes.net/092004/gd0904.htm