Fourier Image Lab
Published in

Fourier Image Lab

Resampling of images and video sequences

Moscow State University, 2001

Bitmap Images

Resolution of digital image

The problem of changing the resolution of images and resampling

Previous research

Aliasing and anti-aliasing

text with anti-aliasing
text without anti-aliasing

An overview of popular filters and interpolation algorithms

Anti-aliasing and resampling filters in 3DS MAX, Photoshop, ACDSee

3DS MAX

3DS MAX anti-aliasing filters

Adobe Photoshop

Adobe Photoshop image resizing options

ACDSee

ACDSee resizing options
  • Rectangular filter
  • Triangular filter
  • Bicubic interpolation
  • Bell
  • Lanczos filter
  • Mitchell filter

Resampling algorithm properties.

Blurring of the image

blurring of the image

Aliasing.

aliasing effect
step overshoot
ringing
Spatial Frequency Ripple

Methods for assessing the quality of resampling algorithms

Assessing resampling quality

Objective

DSP approach to resampling and building a resampling filter.

Construction of filter

Implementation of the Impress

Method

Choosing the compression / stretching ratio

Construction of the resampling filter

n is a region [-N,N]

Kernels and frequency response of filters (illustrations)

Sinc-fucntion
Impress (sharp)
Impress (normal)

Amplitude-frequency characteristics of filters.

Sinc function and preset “Normal”
“Normal” and ”Sharp” presets

Interpolation / Filtering

Optimization

Polyphase filtering

Coefficient caching

ExtraSharp Modification (High definition)

Eliminate the Sampling Frequency Ripple effect.

cutoff frequency and multiples of it

Analytical Rationale

2 filter cores with different parameters B.
blue curve — original filter, pink — corrected
blue curve — original filter, pink — corrected

Resampling with poly-phase structure

Function PreparePoly

Function DoResampling

Function PreparePoly

Detailed description of the polyphase structure

Direct implementation

Polyphase Implementation

Algorithm explanation

Boundary correction

Building adaptive and compositional filters.

The idea of ​​the method

Implementation of the method

mask obtaining process

Illustration of the method

Adaptation of the algorithm for resampling video sequences

Results

Examples of the algorithm and comparison

Example 1.

Image 1. (1024x1536) obtained by scanning a slide.
region for comparison

Example 2.

original image of small resolution

Example 3.

Original image rendered in 3DS MAX 5.0 (1500х1125)
region to match

Summary

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deep dives into frequency guided imaging, understanding image quality, rendering of sensor data for computer and human vision

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