axes2pix

Convert axes coordinates to pixel coordinates

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Syntax

pixelCoord = axes2pix(n,extent,axesCoord)

Description

pixelCoord = axes2pix(n,extent,axesCoord) converts an axes coordinate into an intrinsic ("pixel") coordinate.

Note

You can use the imref2d object to facilitate conversion between intrinsic coordinates, world coordinates, and array indices.

example

Examples

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Open Live Script

Display image.

h = imshow('pout.tif');

Figure contains an axes object. The hidden axes object contains an object of type image.

Get the size of the image.

[nrows,ncols] = size(get(h,'CData'));

Get the image XData and YData.

xdata = get(h,'XData')
xdata = 1×2

     1   240


ydata = get(h,'YData')
ydata = 1×2

     1   291

Convert an axes coordinate into an intrinsic coordinate for the x and y dimensions.

px = axes2pix(ncols,xdata,30)
px = 
30

py = axes2pix(nrows,ydata,30)
py = 
30
Open Live Script

Read an image and display it. Get the size of the image.

I = imread('pout.tif');
[nrows,ncols] = size(I)
nrows = 
291

ncols = 
240

Create a spatial referencing object for this image, with default property settings. By default, the upper-left corner of the image has intrinsic coordinate (1,1).

RI = imref2d(size(I));
h = imshow(I,RI);

Figure contains an axes object. The axes object contains an object of type image.

xData = get(h,'XData')
xData = 1×2

     1   240


yData = get(h,'YData')
yData = 1×2

     1   291

For illustrative purposes, specify an arbitrary image extent in the x- and y-directions. This example shifts the image up by 20 pixels and to the right by 400 pixels. The example also shifts the image to the right by 100 pixels and compresses the image horizontally by a factor of 2.

xWorldLimits = 0.5*xData + 400;
yWorldLimits = yData - 20;
RA = imref2d(size(I),xWorldLimits,yWorldLimits); 
imshow(I,RA)

Figure contains an axes object. The axes object contains an object of type image.

Select a pixel, such as a pixel near the nose of the child. This pixel occurs around the axes coordinate (x, y) = (450, 90) in the modified image.

Convert the axes coordinate to an intrinsic coordinate.

px = axes2pix(ncols,xWorldLimits,450)
px = 
100

py = axes2pix(nrows,yWorldLimits,90)
py = 
110

The intrinsic coordinate of the point is at (100, 110). This agrees with the location of the nose in the original image.

Input Arguments

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Number of image rows or columns, specified as a positive integer. n is the number of image columns for the x-coordinate, or the number of image rows for the y-coordinate.

Image world extent, specified as a 2-element numeric vector. extent is returned by get(image_handle,"XData") or get(image_handle,"YData").

Axes coordinate to convert to intrinsic coordinates, specified as a numeric vector.

Output Arguments

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Intrinsic coordinates, returned as a numeric vector. If all of the input arguments are of data type single, then pixelCoord is of data type single. Otherwise, pixelCoord is of data type double.

Data Types: double | single

Tips

  • axes2pix performs minimal checking on the validity of the n, axesCoord, or extent arguments. For example, axes2pix can extrapolate from extent to return a negative coordinate. The function calling axes2pix bears responsibility for error checking.

Extended Capabilities

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Version History

Introduced before R2006a

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See Also

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