Cirrus Logic CS485 Especificações descarregar pdf (Página 247)

Geometric Transforms

11-25

Discussion

The functions iplWarpPerspective() and iplWarpPerspectiveQ()

warp the source image by a perspective transformation according to the

following formulas:

x’ =(c

·x + c

·y + c

)/(c

·x + c

·y + c

)

y’ =(c

·x + c

·y + c

)/(c

·x + c

·y + c

)

where x and y denote the original pixel coordinates; x’ and y’ denote the

pixel coordinates in the transformed image.

The two functions differ in their third argument:

iplWarpPerspective()

uses a 3-by-3 input array of transform coefficients c

coeff

[m][n],

whereas iplWarpPerspectiveQ() computes the coefficients internally

from the input array

quad

containing coordinates of the reference

quadrangle.

warpFlag

is IPL_R_TO_Q, the functions transform the rectangular ROI

of the source image into the reference quadrangle of the resultant image.

warpFlag

is IPL_Q_TO_R, the functions transform the source quadrangle

into the rectangular ROI of the resultant image.

The interpolation specified by

interpolate

is used for resampling the

input image.

To compute the perspective transform parameters, use these auxiliary

functions:

iplGetPerspectiveBound(), iplGetPerspectiveQuad()

and iplGetPerspectiveTransform(). They are described in the sections

that follow.

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