Version 3.1.3
matplotlib
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matplotlib.colors.makeMappingArray

matplotlib.colors.makeMappingArray(N, data, gamma=1.0)[source]

Create an N -element 1-d lookup table.

This assumes a mapping \(f : [0, 1] \rightarrow [0, 1]\). The returned data is an array of N values \(y = f(x)\) where x is sampled from [0, 1].

By default (gamma = 1) x is equidistantly sampled from [0, 1]. The gamma correction factor \(\gamma\) distorts this equidistant sampling by \(x \rightarrow x^\gamma\).

Parameters:
N : int

The number of elements of the created lookup table. This must be N >= 1.

data : Mx3 array-like or callable

Defines the mapping \(f\).

If a Mx3 array-like, the rows define values (x, y0, y1). The x values must start with x=0, end with x=1, and all x values be in increasing order.

A value between \(x_i\) and \(x_{i+1}\) is mapped to the range \(y^1_{i-1} \ldots y^0_i\) by linear interpolation.

For the simple case of a y-continuous mapping, y0 and y1 are identical.

The two values of y are to allow for discontinuous mapping functions. E.g. a sawtooth with a period of 0.2 and an amplitude of 1 would be:

[(0, 1, 0), (0.2, 1, 0), (0.4, 1, 0), ..., [(1, 1, 0)]

In the special case of N == 1, by convention the returned value is y0 for x == 1.

If data is a callable, it must accept and return numpy arrays:

data(x : ndarray) -> ndarray

and map values between 0 - 1 to 0 - 1.

gamma : float

Gamma correction factor for input distribution x of the mapping.

See also https://en.wikipedia.org/wiki/Gamma_correction.

Returns:
lut : array

The lookup table where lut[x * (N-1)] gives the closest value for values of x between 0 and 1.

Notes

This function is internally used for LinearSegmentedColormaps.