How to Use Histograms modified

8/7/2019 How to Use Histograms modified

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How to Use Histograms

HISTOGRAM HISTORY

In statistics, a histogram is a graphical representation, showing a visualimpression of the distribution of experimental data. It is an estimate of the

probability distribution of a continuous variable and was first introduced by Karl

Pearson. A histogram consists of tabular frequencies, shown as adjacent rectangles,

erected over discrete intervals (bins), with an area equal to the frequency of the

observations in the interval. The height of a rectangle is also equal to the frequency

density of the interval, i.e., the frequency divided by the width of the interval. The

total area of the histogram is equal to the number of data. A histogram may also be

normalized displaying relative frequencies. It then shows the proportion of cases

that fall into each of several categories, with the total area equaling 1. The

categories are usually specified as consecutive, non-overlapping intervals of avariable. The categories (intervals) must be adjacent, and often are chosen to be of

the same size.

Histograms are used to plot density of data, and often for density estimation:

estimating the probability density function of the underlying variable. The total

area of a histogram used for probability density is always normalized to 1. If the

length of the intervals on the x-axis are all 1, then a histogram is identical to a

relative frequency plot.

An alternative to the histogram is kernel density estimation, which uses a kernel to

smooth samples. This will construct a smooth probability density function, which

will in general more accurately reflect the underlying variable.

The histogram is one of the seven basic tools of quality control.

INTRODUCTION

The best way to evaluate exposure is to look at the picture, not a histogram.

Histograms are a way to measure exposure more objectively for those who can't

see very well. Histograms don't replace your eyes and experience. Histograms are

helpful in sunlight where it's hard to see an LCD, or in the shop if setting

something exactly. Your eyes are always the final judge.


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A histogram is just a guide. Worry about your image more than the histogram.

Definition

Step-column chart that displays a summary of the variations in (frequencydistribution of) quantities (called Classes) that fall within certain lower and upper

limits in a set of data. Classes are measured on the horizontal ('X') axis, and the

number of times they occur (or the percentages of their occurrences) are measured

on the vertical ('Y') axis. To construct a histogram, rectangles or blocks are drawn

on the x-axis (without any spaces between them) whose areas are proportional to

the classes they represent. Histograms (and histographs) are used commonly where

the subject item is discrete (such as the number of students in a school) instead of

being continuous (such as the variations in their heights). Also called frequency

diagram, a histogram is usually preferred over a histograph where the number of

classes is less than eight.HISTOGRAM BASICS

A histogram is a graph counting how many pixels are at each level between black

and white.

Black is on the left. White is on the right.

The height of the graph at each point depends on how many pixels are that bright.

Lighter images move the graph to the right. Darker ones move it to the left. Easy!

More Pixels

Fewer Pixels

Black - Dark - Medium - Light -

White

A Histogram


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A good image often, but not always, has a histogram spread all over.

Histographs

A histogram graphs continuous data by frequencies. The data is divided into bins

to make bars.

Bar Graphs

A bar graph displays discrete data with bars. The height represents the quantity of

the data.

Similaritiesand Differences

Both histograms and bar charts have bars a varying heights. Histograms differ in

look--the bars are next to each other with no gaps and the height of the bars followa curve like a hill. The bars on bar graphs are separated and the heights of the bars

can vary like jagged glass.

Whento Use

Use a histogram for continuous data like how many males for each age group. Use

a bar graph for discrete data like how many types of vehicles were made in a year.

HistoryofHistogram

Karl Pearson first proposed the name histogram in his lectures published in 1895.

He gave the name histogram to refer to a common form of graphical

representation.

HistoryofBar Graphs

According to "History of Histograms" by Yannis Ionnidis (2003), the oldest

known bar chart appeared in a book by Scottish political economist William

Playfair titled "The Commercial and Political Atlas" (1786).


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Histogram. This histogram represents data on the cross-sectional area of 30 erratics (boulders left behind

by retreating glaciers). Note the use of wider intervals for the classes corresponding to the scarcer larger

boulders. In a histogram, area is proportional to frequency.

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How to Use Histograms modified