Histogram Computation and Display

Author: abidrahmank

Learning_OpenCV-Python/example_7_1.py

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+''' example_7_1.py 
+
+Referred to example 7.1 in the book "Learning OpenCV: Computer Vision with the OpenCV Library"
+
+Example 7-1. Histogram computation and display
+
+usage: python example_7_1.py <image>
+
+Converted by Abid.K	--mail me at [email protected]
+'''
+################################################################################################
+
+import cv,sys
+
+if len(sys.argv)==2 and (cv.LoadImage(sys.argv[1])!=0):
+	src=cv.LoadImage(sys.argv[1])
+	hsv=cv.CreateImage(cv.GetSize(src),8,3)
+
+	cv.CvtColor(src,hsv,cv.CV_BGR2HSV)
+	h_plane=cv.CreateImage(cv.GetSize(src),8,1)
+	s_plane=cv.CreateImage(cv.GetSize(src),8,1)
+	v_plane=cv.CreateImage(cv.GetSize(src),8,1)
+
+	planes=[h_plane,s_plane]
+
+	cv.CvtPixToPlane(hsv,h_plane,s_plane,v_plane,None)
+
+	h_bins=30
+	s_bins=32
+
+#	Build the histogram and compute its contents.
+
+	hist=cv.CreateHist([h_bins,s_bins],cv.CV_HIST_ARRAY,[(0,180),(0,255)],1)
+	cv.CalcHist(planes,hist,0,None)
+	cv.NormalizeHist(hist,1.0)
+
+#	Create an image to use to visualize our histogram.
+
+	scale=10
+	hist_img=cv.CreateImage((h_bins*scale,s_bins*scale),8,3)
+	cv.Zero(hist_img)
+
+	max_value=0
+	(minvalue,maxvalue,minidx,maxidx)=cv.GetMinMaxHistValue(hist)
+
+	for h in range(h_bins):
+		for s in range(s_bins):
+			bin_val=cv.QueryHistValue_2D(hist,h,s)
+			intensity=cv.Round(bin_val*255/maxvalue)
+			cv.Rectangle(hist_img,(h*scale,s*scale),((h+1)*scale-1,(s+1)*scale-1),(intensity,intensity,intensity),cv.CV_FILLED)
+			print intensity	
+
+	cv.ShowImage("src",src)
+	cv.ShowImage("hsv",hist_img)
+	cv.WaitKey(0)
+
+else:
+	print "usage : python example_7_1.py <image>"
+