GetHistogram
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Description

Returns the histogram of the current image frame over a selected ROI .


Syntax


[VB]
Value=objActiveDcam.GetHistogram(Component [,Bins, Step ])


[C/C++]
HRESULT GetHistogram( VARIANT* pHistogram, short Component, long Bins=256, short Step=1 );


Data Types
[VB]

Channel : Integer
Bins : Long
Step
: Integer
Return value: Variant (Array)


Parameters
[C/C++]

Component [in]  
Enumerated integer specifying the color component for which the histogram data are obtained. This parameter is disregarded for grayscale images. Must be one of the following values:  
0 - collects the histogram of the luminance of the image  
1 - collects the histogram of the red component of the image  
2 - collects the histogram of the green component of the image  
3 - collects the histogram of the blue component of the image  
 
Bins [in]  
Number of intervals used for histogram collection. It is recommended to set this parameter to a number of possible intensity levels in the image or to an integer fraction of that value, otherwise some precision will be lost due to averaging that occurs within the consolidated bins. A typical number of histogram bins for 8-bit and 16=bit images will be 256.  

Step [in]  
An optional integer between 1 and 16 specifying the sampling step, which is used to collect pixel values for the histogram calculations. If this number is 1, every pixel is taking into consideration. If the number is 2, every second pixel in a row will be skipped, as well as every second row in the image, etc. Increasing the sampling step raises the speed of the histogram calculations, but sacrifices some accuracy.  
 
pHistogram [out,retval]  
Pointer to the SAFEARRAY containing the histogram values.  
 
 
Return Values

S_OK  
Success  
E_FAIL  
Failure.  


Example


This VB example retrieves the histogram of the red component per each frame acquired:

Private Sub
 ActiveDcam1_FrameAcquired()

ActiveDcam1.SetROI 100,100,500, 400 

HistArray=ActiveDcam1.GetHistogram (1, 256)
End Sub



Remarks


The histogram is calculated over the rectangular region of interest defined by SetROI. The luminance thresholds of the current ROI are disregarded. If the ROI is not set, the whole image frame will be used.