pcolor (MATLAB Functions)

Pseudocolor plot

Syntax

pcolor(C)
pcolor(X,Y,C)
pcolor(axes_handle,...)
h = pcolor(...)

Description

A pseudocolor plot is a rectangular array of cells with colors determined by C. MATLAB creates a pseudocolor plot using each set of four adjacent points in C to define a surface rectangle (i.e., cell).

The default shading is faceted, which colors each cell with a single color. The last row and column of C are not used in this case. With shading interp, each cell is colored by bilinear interpolation of the colors at its four vertices, using all elements of C.

The minimum and maximum elements of C are assigned the first and last colors in the colormap. Colors for the remaining elements in C are determined by a linear mapping from value to colormap element.

pcolor(C) draws a pseudocolor plot. The elements of C are linearly mapped to an index into the current colormap. The mapping from C to the current colormap is defined by colormap and caxis.

pcolor(X,Y,C) draws a pseudocolor plot of the elements of C at the locations specified by X and Y. The plot is a logically rectangular, two-dimensional grid with vertices at the points [X(i,j), Y(i,j)]. X and Y are vectors or matrices that specify the spacing of the grid lines. If X and Y are vectors, X corresponds to the columns of C and Y corresponds to the rows. If X and Y are matrices, they must be the same size as C.

pcolor(axes_handles,...) plots into the axes with handle axes_handle instead of the current axes (gca).

h = pcolor(...) returns a handle to a surface graphics object.

Remarks

A pseudocolor plot is a flat surface plot viewed from above. pcolor(X,Y,C) is the same as viewing surf(X,Y,0*Z,C) using view([0 90]).

When you use shading faceted or shading flat, the constant color of each cell is the color associated with the corner having the smallest x-y coordinates. Therefore, C(i,j) determines the color of the cell in the ith row and jth column. The last row and column of C are not used.

When you use shading interp, each cell's color results from a bilinear interpolation of the colors at its four vertices, and all elements of C are used.

Examples

A Hadamard matrix has elements that are +1 and -1. A colormap with only two entries is appropriate when displaying a pseudocolor plot of this matrix.

pcolor(hadamard(20))
colormap(gray(2))
axis ij
axis square

A simple color wheel illustrates a polar coordinate system.

n = 6;
r = (0:n)'/n;
theta = pi*(-n:n)/n;
X = r*cos(theta);
Y = r*sin(theta);
C = r*cos(2*theta);
pcolor(X,Y,C)
axis equal tight

Algorithm

The number of vertex colors for pcolor(C) is the same as the number of cells for image(C). pcolor differs from image in that pcolor(C) specifies the colors of vertices, which are scaled to fit the colormap; changing the axes clim property changes this color mapping. image(C) specifies the colors of cells and directly indexes into the colormap without scaling. Additionally, pcolor(X,Y,C) can produce parametric grids, which is not possible with image.

See Also

caxis, image, mesh, shading, surf, view

pcode pdepe