GetImagePointer

Description

Returns the pointer to the pixel at the specified coordinates of the current frame.


Syntax

[VB]
Value=objActiveDcam.GetImagePointer( X, Y )

[C/C++]
HRESULT GetImagePointer( short X, short Y, VARIANT* pValue );


Data Types [VB]

X: Integer
Y: Integer
Return value: Variant (pointer)


Parameters [C/C++]

X [in]

The x-coordinate of the pixel

Y [in]

The y-coordinate of the pixel

pValue [out,retval]

Pointer to the variant contating the pointer to the specified memory location

Return Values

S_OK

Success

E_FAIL

Failure.

E_INVALIDARG

Invalid input arguments.

Example

This C++ example grabs a frame, retrieves a pointer to the 32th line in the frame memory and copies the pixels values into a byte array . A wrapper class CActiveDcam is used to access the ActiveDcam control:

BYTE line[4096];
int iWidth=m_ActiveDcam.GetSizeX;
int iHeight=m_ActiveDcam.GetSizeY;
m_ActiveDcam.Grab()
VARIANT v=m_ActiveDcam.GetImagePointer(0,32);
BYTE* ptr=ActiveDcam1.GetImagePointer(0,32);
memcpy(&line,v.pcVal,iWidth);
This C# example uses the FrameAcquired event to retrieve a pointer to the 32th line in the frame memory and change pixel values in the line to zeros:

private void axActiveDcam1_FrameAcquired(object sender, AxACTIVEDCAMLib._IActiveDcamEvents_FrameAcquiredEvent e)
{
int sx=axActiveDcam1.SizeX;
object obj=axActiveDcam1.GetImagePointer(0, iHeight-1-32);
int a = (int)obj;
byte* ptr= (byte*)a;
for (int x=0; x<sx; x++, ptr++)
 *ptr=0;
}

Remarks

The GetImagePointer method provides the most efficient way to quickly access the internal image buffer in pointer-aware programming languages. Unlike GetImageData, this method doesn't modify original pixel values of high-bit depth images. The number of bytes in each line of the image buffer depends on the format and horizontal size of the video as specified in the following table:

Format	Line width in bytes
8-bit monochrome	SizeX
16-bit monochrome	SizeX * 2
24-bit RGB	SizeX * 3
48-bit RGB	SizeX * 6

Note that ActiveDcam automatically converts YUV video outputed by a camera to 24-bit RGB.

Images in ActiveDcam are stored bottom up, therefore the zero vertical coordinate corresponds to the bottom line of the image.

The values of the x and y coordinates must not exceed the width and height of the video frame, or the error will occur.