Dynamic Range Compression

An example using the 16 bit M51 image. Phase preserving dynamic range compression allows the scale of analysis to be controlled. Here we process the image at wavelengths up to 50 pixels and up to 200 pixels. Longer wavelengths allow larger structures to be seen. Small wavelengths allow fine structures to be seen. Note the image size is (510, 320).

using TestImages
using Images
using ImageContrastAdjustment
using ImagePhaseCongruency

img = float64.(testimage("m51"))

# Histogram equalization for reference (with a very large number of bins!)
img_histeq = histeq(img, 100_000)

# Phase presserving dynamic range compression at cutoff wavelengths of 50 and
# 200 pixels.  Note we scale the image because its raw values are between 0 and
# 1, see the help information for ppdrc() for details.
scale = 1e4
img_ppdrc1 = ppdrc(img*scale, 50)
img_ppdrc2 = ppdrc(img*scale, 200)

mosaic(
    adjust_histogram(img, LinearStretching()),
    adjust_histogram(img_histeq, LinearStretching()),
    adjust_histogram(img_ppdrc1, LinearStretching()),
    adjust_histogram(img_ppdrc2, LinearStretching()),
    nrow=1
)

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