Decorrelation Stretching

Decorrelation stretching is an image enhancement technique used to improve color contrast in multispectral remote sensing images. It reduces the correlation between image bands and spreads out (stretches) their color values so that features become easier to see.

It is mainly used to enhance true-color or false-color composite images.

Why Is It Needed?

Remote sensing bands often have strong correlations.
For example:

Red and NIR bands both reflect strongly from vegetation
Visible bands (R, G, B) reflect similarly from many surfaces

Because of this correlation:

Images look dull, low-contrast, or washed-out
Important features become hard to distinguish

Decorrelation stretching solves this by reducing band-to-band correlation and enhancing color differences.

How Decorrelation Stretching Works

1. Identify the Correlation Between Bands

Multispectral bands often show similar brightness patterns.
This makes the composite image look flat.

2. Transform to a New Coordinate Space

Using a statistical method like Principal Component Analysis (PCA), the data is rotated to reduce correlation.

This step:

Separates mixed color information
Produces independent principal components

3. Stretch the Data (Increase Contrast)

Each principal component is stretched using a contrast enhancement method:

linear stretch
standard deviation stretch

This makes color differences more visible.

4. Transform Back to Original Color Space

After stretching, the data is rotated back to the original R–G–B space.

Result:

Colors are more vibrant
Features become clearer
Objects with slight spectral differences appear strongly different

Before Decorrelation Stretching	After Decorrelation Stretching
Dull color composite	Bright, colorful composite
Bands highly correlated	Bands decorrelated
Less visible features	Enhanced feature separation
Washed-out colors	Natural-looking sharp colors

Band correlation: How similar two bands are in brightness.
Stretching: Expanding pixel value ranges to increase contrast.
PCA (Principal Component Analysis): Statistical method to reduce correlation.
Color enhancement: Improvement of visible color separation.

Decorrelation stretching is an image enhancement technique that reduces correlation between spectral bands and stretches their color values to improve visual contrast. It is commonly used for multispectral images to highlight subtle color differences and improve feature detection.

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