matlab有兩個生成直方圖的庫函數，分別是imhist和histogram，二者有何區別呢？

區別就是：

imhist

官方help：imhist(I) calculates the histogram for the intensity image I and displays a plot of the histogram. The number of bins in the histogram is determined by the image type.
可見，imhist的NumBins值是由圖像類型決定的。若圖像為uint8類型，則bin的數量為256，即[0:1:255]。

histogram（早期版本為hist，現在matlab已不建議使用hist了）

官方help：
histogram(X) creates a histogram plot of X. The histogram function uses an automatic binning algorithm that returns bins with a uniform width, chosen to cover the range of elements in X and reveal the underlying shape of the distribution. histogram displays the bins as rectangles such that the height of each rectangle indicates the number of elements in the bin.

nbins — Number of bins
　　 Number of bins, specified as a positive integer. If you do not specify nbins, then histogram automatically calculates how many bins to use based on the values in X.

可見，histogram的NumBins值可以人為設定，在未指定該參數時，系統將基于圖像的灰度分布自動計算NumBins的值。

例程：

 1 imgColor = imread('lena.jpg');
 2 imgGray = rgb2gray(imgColor);
 3 
 4 %% imhist
 5 figure('name', 'imhist'),
 6 imhist(imgGray);
 7 
 8 %% histogram
 9 figure('name', 'histogram auto'),
10 % histogram函數自動計算NumBins值
11 hist2 = histogram(imgGray);
12 % Find the bin counts
13 binCounts = hist2.Values;
14 % Get bin number
15 binNum = hist2.NumBins;
16 
17 %% histogram 指定NumBins值
18 % Specify number of histogram bins
19 figure('name', 'histogram256'),
20 hist256 = histogram(imgGray, 256); % 等同于 imhist(imgGray)

由運行結果也可看出，histogram(imgGray, 256)與imhist(imgGray)，二者在最大bin的灰度累計值是一樣的。

reference

http://www.ilovematlab.cn/thread-13665-1-1.html

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