Introduction to Understanding

Your Histogram

By Tibor Vari

President of Teaneck Camera Club 2005-2006 & 2006-2007, VP 2003-2004, 2004-2005

First VP of NJFCC 2007-2008

Salon Worker: Slides/Digital, Nature, Color Prints By The Maker

Numerous Medals, MAs & HMs in Club, NJFCC & PSA competitions

Landscape Workshop Tour Guide, Judge, Youth Sports, Weddings, Proms, Home Family Portraits

Winter in Yosemite Feb 20-24, 2013

I have had a 35mm since I was 18 (Olympus OM1 & OM2)

08/1993 Nikon N6006,

05/1995 Nikon N90, 08/1996 Nikon N90s,

05/2000 Nikon F100, 02/2001 Nikon F5,

11/2001 Canon G2 Digital, 09/2004 Nikon D70 Digital,

04/2005 Nikon D2x (100% digital with Nikon F5 & F100 sold 02/2006),

04/2007 Nikon D200,

08/2008 Nikon D700

Tibor Vari’s website is at http://www.tiborvari.com Email: tibor@tiborvari.com

Introduction to

UnderstandingYour

Digital Camera’s Histogram

ByTibor Vari

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

Agenda

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 5-6 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!

Dynamic Range of Light Values

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

Shutter SpeedsShutter 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” 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 LightFreeze Action <-Silky Water-> Low Light

Lots of sunlight F11-F22Lots of sunlight F11-F22

Wide Open Apertures Slow Film (ISO 50) Wide Open Apertures Slow Film (ISO 50)

Fast Film (ISO 400+) Fast Film (ISO 400+) Narrow Apertures Narrow Apertures

F StopsF Stops

F1.4 2.8 4 5.6 8 11 16 22 32F1.4 2.8 4 5.6 8 11 16 22 32

Portraits Landscapes Portraits Landscapes

Shallow DOF Great DOF Shallow DOF Great DOF

Background blurred Everything sharpBackground blurred Everything sharp

ISOISO

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

50 100 200 400 800 1600 320050 100 200 400 800 1600 3200

3 Way Tug of War

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.

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

40 colored tiles represented by the histogram

Where the shadows, midtones and highlights fall within the histogram

http://clarkvision.com/imagedetail/does.pixel.size.matter/ by R N Clark

Pixel sensor collects light while shutter is open

Digital Histogram on a D2xCamera 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

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

This image is well exposed though a bit flat.

The black shadow and white highlights are virtually nil.

Highlights

238 R

232 G

220 B

Mid-tone

118 R

124 G

136 BShadow

24 R

23 G

18 B

Sample Image

Pixel count high for sky

R16, G13, B12

R144G160B175

R249G186B89

Sample Image

.6 second at F22, ISO 100, 24mm

R67G60B54

R2G2B2

R255G213B171

Sample Image

¼ second at F18, ISO 100, 200mm

Blown Shadows & Highlights #1

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

1, 2 & 3 Stop Neutral Density Filters

Image from: http://www.luminous-landscape.com/tutorials/understanding-grads.shtml

Blown Shadows & Highlights #2

Exposed for mountain

Blown Shadows

Black Pixel count

Exposed for foreground

Blown Highlights

White Pixel count

Merged in Photoshop

Added Saturation, curves

Contrast, Adj Levels

Typical histogram examples

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

“Blinkies'”

Interpreting your Histogram

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.

(High Key sample)

Interpreting your Histogram

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.

(High Key sample)

1/500 second at F5.6, ISO 200, 105mm

(Low Key Sample)

ISO 800

F16

.2s (1/5)

A Mode

ISO 800

F16

.2s (1/5)

+.5 comp

A Mode

Note:

Highlights clipped,

No software can recover details from clipped shadows or highlights

ISO 200

F16

.8s

A Mode

ISO 200

F8

.2s

A Mode

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

Interpreting your Histogram

Tough Images

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

Whites not clipped so detail is retained

A Couple of Myths

• A perfect histogram is a camel back!

• Better to underexpose – you can always bring it back up in Photoshop!

Summary• The histogram is a powerful tool to help you

properly expose your images!• 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

• 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

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.

Histogram 201

Concept: Expose to the righthttp://www.luminous-landscape.com/tutorials/expose-right.shtml