A basic introduction to histograms

1. 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

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

3. Digital/Film Basics
Color by Numbers
Dynamic Range
So What is a Histogram?
Samples
Myths
Summary
Sources
Agenda

4. 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

5. 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!

6. Dynamic Range of Light Values

7. 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

8. 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
3 Way Tug of War

9. 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.

10. 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

11. http://clarkvision.com/imagedetail/does.pixel.size.matter/ by R N Clark
Pixel sensor collects light
while shutter is open

12. Digital Histogram on a D2x
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

13. 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.

14. Highlights
238 R
232 G
220 B
Mid-tone
118 R
124 G
136 B
Shadow
24 R
23 G
18 B
Sample Image
Pixel count
high for sky

15. R16,
G13,
B12
R144
G160
B175
R249
G186
B89
Sample Image
.6 second at F22, ISO 100, 24mm

16. R67
G60
B54
R2
G2
B2
R255
G213
B171
Sample Image
¼ second at F18, ISO 100, 200mm

17. 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

18. 1, 2 & 3 Stop Neutral Density Filters
Image from: http://www.luminous-landscape.com/tutorials/understanding-grads.shtml

19. 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

20. Typical histogram examples

21. http://www.dpreview.com/learn/?/key=histogram By Vincent Bockaert
“Blinkies'”

22. 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)

23. 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

24. (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

25. Tough Images
Note: Image from http://www.naturescapes.net/092004/gd0904.htm by Greg Downing
Whites not
clipped so
detail is
retained

30. A Couple of Myths
• A perfect histogram is a camel back!
• Better to underexpose – you can always
bring it back up in Photoshop!

31. 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)

32. 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 right
http://www.luminous-landscape.com/tutorials/expose-right.shtml