Shift-invariant optics examples

This script illustrates how to create an optics structure used for the shift-invariant optics calculations. It also illustrates how to place that optics structure into the Optics window (optical image window) and run the calculation.

Three examples are below. One creates a simple pillbox (averaging) PSF. The second creates a simple sharpening filter. The third illustrates the built-in ability to create a series of Gaussian blur filters with a spread that varies with wavelength and with different x- and y-dimension spread ratios.

You can use this script as a model for creating the optics structure of a shift-invariant lens. After creating the psf data, we suggest that you save the data in a file called SI-yourLensName within the directory data\optics. The file format for the data, illustrated below, is very simple. The save procedure is described in the routine ieSaveSIDataFile (see below). We suggest you use ieSaveSIDataFile to save your shift-invariation point spread data.

You can load those data into the optical image window directly (Optics | Load SI Data). Or, you can use this script to create the optics and save those from the window using Optics | Export, or you can simply save the optics using vcSaveObject.

Copyright ImagEval Consultants, LLC, 2008



Example 1: Create a shift-invariant optics structure with custom PSF data.

% The structure is created using a set of point spread functions.
% The point spread functions are a set of matrices defined on a
% grid.  THere is one point spread for each wavelength.  In this
% example, there are 31 wavelengths (400:10:700).  The point
% spread functions are simply random numbers.  The grid is 128 x
% 128 with samples spaced every 0.25 microns. Hence, the total
% grid size is 32 microns on a side.

Create a simple test scene

% Let's work with a small checkerboard scene
pixPerCheck = 16;
nChecks = 6;
scene = sceneCreate('checkerboard',pixPerCheck,nChecks);
wave  = sceneGet(scene,'wave');
scene = sceneSet(scene,'fov',3);

% Replace the optical image into your ISET window

Create Shift-invariant data

% Now, write out a file containing the relevant point spread function
% data, along with related variables.
umPerSample = [0.25,0.25];                % Sample spacing

% Point spread is a little square in the middle of the image
h = zeros(128,128); h(48:79,48:79) = 1; h = h/sum(h(:));
psf = zeros(128,128,length(wave));
for ii=1:length(wave), psf(:,:,ii) = h; end     % PSF data

% Save the data

Read the custom data and put it into an optics structure.

oi = oiCreate;
optics = siSynthetic('custom',oi,'SI-pillBox',[]);

% Make sure the program knows you want to use shift invariant
optics = opticsSet(optics,'model','shiftInvariant');

% Attach the optics structure to the optical image structure
oi = oiSet(oi,'optics',optics);

% You can now compute using your current scene.
oi = oiCompute(scene,oi);
oi = oiSet(oi,'name','Pillbox');

% Show the OI window

% Use Analyze | Optics | XXX to plot various functions in the optics
% (optical image) window.

Example 2: Create a a slight sharpening filter.

h1 = fspecial('gaussian', 128, 5);
h2 = fspecial('gaussian', 128, 10);
h = h1 - 0.5*h2;
% figure(1); mesh(h)

psf = zeros(128,128,length(wave));
for ii=1:length(wave), psf(:,:,ii) = h; end     % PSF data

% Save the data and all the rest, in compact form

optics = siSynthetic('custom',oi,'customFile','deleteMe');
optics = opticsSet(optics,'model','shiftInvariant');
oi     = oiSet(oi,'optics',optics);

oi = oiCompute(scene,oi);
oi = oiSet(oi,'name','Sharpened');

Example 3: Create a wavelength-varying shift-invariant gaussian PSF

wave    = oiGet(oi,'wave');
psfType = 'gaussian';

% The special set up for the wavelength-dependent Gaussian spread functions
% is illustrated here.

%We set the spread as a function of wavelength.  This function is
%arbitrary - it makes the long wavelength much worse than the
waveSpread = (wave/wave(1)).^3;

% Make point spreads with a symmetric Gaussian
xyRatio = ones(1,length(wave));

% Now call the routine with these parameters
optics  = siSynthetic(psfType,oi,waveSpread,xyRatio,'gaussPSF');

% Here is the rest of the computation, as above
optics  = opticsSet(optics,'model','shiftInvariant');
oi      = oiSet(oi,'optics',optics);
scene   = vcGetObject('scene');
oi      = oiCompute(scene,oi);

oi = oiSet(oi,'name','Chromatic Gaussian');

We saved these shift invariant optics using:

%   fullName = fullfile(isetRootPath,'data','optics','si2x1GaussianWaveVarying');
% (or)
%   fullName = fullfile(isetRootPath,'data','optics','siGaussianWaveVarying');
%   vcExportObject(optics,fullName)
% You can import these optics using:  Optics | Import Optics
% Use Analyze | Optics | PSF Mesh to see the point spread a different
% wavelengths
% Use Analyze | Line x Wave Plot to see the loss of contrast a long
% wavelengths compared to short wavelengths

Loading (2x1) asymmetric optics data from a file

fullName = fullfile(isetRootPath,'data','optics','si2x1GaussianWaveVarying.mat');
newVal   = vcImportObject('OPTICS',fullName);
oi       = vcGetObject('oi');
oi       = oiCompute(scene,oi);

oi = oiSet(oi,'name','Asymmetric Gaussian');

View multiple oi images