MATLAB VIDEO AND IMAGE PROCESSING BLOCKSET 3 Guia do Utilizador descarregar pdf (Página 29)

Key Blockset Con cepts

positions. Seco nd, the spatial coordinates of the cente r point of any p ix el are

identical to the pixel coordinates for that pixel. However, the pixel coordinate

system is discrete, while the spatial coordinate system is continuous. T his

means that, in pixel coordinates, the upper-left corner of an image is (0,0),

while in spatial coordinates, this location is (-0.5,-0.5). The spatial coordinate

system used by Video and Imag e Processing Blockset differs from the one

used by Image Processing Toolbox. For more informatio n on this spatial

coordinate system, see “Spatial Coordinates” in the Image Pro cessing Toolbox

documentation.

Image Data Stored in Column-Major Format

MATLABandVideoandImageProcessing Blockset use a column-major

numbering scheme to represent data elements internally. That means that

they internally store data elements from the first column first, then data

elements from the second column s econ d, and so on through the last column.

If you have imported an image or a v ideo stream into the MATLAB workspace

using a function from MATLAB or Image Processing Toolbox, the Video and

Image Processin g Blockset b locks will display this image or video stream

correctly. If you have written your own function or code to import images into

MATLAB, you must take the column-major convention into account.

Sample Time

Because the Video and Image Processing blocks calculate values directly

rather than solving differential equations, you m ust configure the Simulink

Solver to behave like a s che duler. The following steps show yo u how to do this:

1 From the m odel’s Simulation menu, select Configuration Parameters.

The Configuration dialog box opens.

2 From the Type list, choose Fixed-step.

3 From th e Solver list, choose discr ete (no cont inu ous states).

The following figure shows the correctly configured Configuration dialog

box.

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MATLAB VIDEO AND IMAGE PROCESSING BLOCKSET 3 Guia do Utilizador Página 29