====== Enhancement – Stretch ======
Stretch adjusts the contrast of the input image. Choose one of four operators: linear, sqrt, log or threshold.

===== Linear =====
{{ :basic_level:enhancement:hoku_basic_stretch_1.png?nolink&400|Stretch with the linear operator}}
A **linear** stretch computes the histogram of the image and stretches the contrast linearly between two percentage points, given in "limits" as min;max. The default is from the bottom 5% of the histogram to the top 95%. The limits are percentages between 0 and 100, and can be whole or decimal numbers.

If the **luminance** flag is checked, the histogram is computed from the luminance of a multiband image. For color images, the luminance is L = 0.3 R + 0.6 G + 0.1 B.

The linear operator works on 8-bit or 16-bit integer images, and its output is the same type as the input.

===== Square root and log =====
**sqrt** and **log** take the square root or the logarithm of the input pixel values. The output is floating point. The input values must not be negative.

===== Threshold =====
{{ :basic_level:enhancement:hoku_basic_stretch_2.png?nolink&400|Stretch with the threshold operator}}
**threshold** outputs an 8-bit unsigned integer image with pixel values of 255 or 0: 255 where the pixel value is greater than the threshold, and 0 where it is less than or equal to it.

You must enter the threshold values: either one value for each input band, or a single value that is applied to all bands.