# Documentation

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# pcolor

Pseudocolor (checkerboard) plot

## Syntax

```pcolor(C) pcolor(X,Y,C) pcolor(axes_handles,...) 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.

## Examples

collapse all

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```

## Tips

A pseudocolor plot is a flat surface plot viewed from above. `pcolor(X,Y,C)` is the same as viewing `surf(X,Y,zeros(size(X)),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.

## Algorithms

Use the `pcolor`, `image`, or `imagesc` function to display image data. Each function displays a rectangular array of cells and uses `C` to determine the colors.

• `pcolor(C)` uses the values in `C` to define the vertex colors by scaling the values to map to the full range of the colormap. The size of `C` determines the number of vertices. `pcolor` determines the cell colors using the colors defined at the cell vertices.

• `image(C)` uses `C` to define the cell colors by mapping the values directly into the colormap. The size of `C` determines the number of cells.

• `imagesc(C)` uses `C` to define the cell colors by scaling the values to map to the full range of the colormap. The size of `C` determines the number of cells.

`pcolor(X,Y,C)` can produce parametric grids, which is not possible with `image` or `imagesc`.