axes2pix

Convert axes coordinates to pixel coordinates

Syntax

pixelCoord = axes2pix(n,extent,axesCoord)

Description

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

Note

The imref2d object has several methods that facilitate conversion between intrinsic coordinates, world coordinates and array indices.

Examples

Convert Axes Coordinate into Intrinsic Coordinate

Display image.

h = imshow('pout.tif');

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

Convert Axes Coordinate to Intrinsic Coordinate with Nondefault XData and YData

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);

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)

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

n — Number of image rows or columns

positive integer

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.

extent — Image world extent

2-element numeric vector

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

axesCoord — Axes coordinates to convert

numeric vector

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

Output Arguments

pixelCoord — Intrinsic coordinates

numeric vector

Intrinsic coordinates, returned as a numeric vector.

Data Types: double

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.

Version History

Introduced before R2006a