Name

image_decimate - Decimate 2-D image by an integer factor.

Usage

output = image_decimate(image, decimation_ratio, fit_to_fft, frequency_low, frequency_high)

Input

image: image to be decimated
decimation_ratio: image decimation ratio (should be >1, function will not return size increased image)
fit_to_fft: window image to FFT friendly size or not (default False).
frequency_low: low pass filter starting frequency
frequency_high: low pass filter stop frequency

Output

output: image reduced to 1/decimation_ratio size.

Options

fit_to_fft

=1 fit to FFT friendly size using smallprime function `X_(fft), Y_(fft) = 2^i*3^j*5^k <= X ,Y `.

else directly apply filter and decimation without size modification.

Description

Image size fit to FFT will speed up the image filtration.
This function usually is applied to reduce size of large images

Method

Input image is low-passed filtered using a Butterworth low-pass filter to the limiting fequency calculated fromt the decimation ratio and subsequently is decimated (every decimation_ratio's sample is selected). Output image size is the integer less equal to the input image size divided by the decimation ratio.

If fit_to_fft is True, both input and out images are windowed to the neares FFT-friendly size currently set as a product of 2, 3, and 5. Please see function smallprime in fundamentals.py for details - the number of primes used can be changed there. UTILITIES

Author / Maintainer

Zhong Huang

Keywords

category 1: FUNDAMENTALS

Files

fundamentals.py

Maturity

alpha: works

Bugs

None. It is perfect.