Introduction to ISET objects and functions: The optical image (OI)

ISET is organized around several key objects (scene, optics, sensor and processor) that reflect the important parts of the image acquisition pipeline. The ISET methods generally rely on calculating with these objects. By using these objects properly, the code and analysis are much easier to understand.

ISET tutorials and scripts involve accessing these simple objects. The first tutorial in this series is t_Introduction.

This script introduces the ISET object "optical image" or OI. The OI describes the irradiance field at the sensor surface. It is computed from the scene (radiance), and the optics. The optics object is stored in a slot within the optical image.

Use t_"TAB KEY" to see the list of tutorials Use s_"TAB KEY" to see the list of ISET scripts.

Copyright ImagEval Consultants, LLC, 2012.

Contents

Initialize ISET

s_initISET

Create a point array scene

These are useful for examining simple optical properties

scene = sceneCreate('pointarray');   % Creates an array of points
scene = sceneSet(scene,'hfov',1);    % 1 deg field of view
vcAddAndSelectObject(scene); sceneWindow;

Create and show an optical image

ISET has several optics models that you can experiment with. These include shift-invariant optics, in which there is a different shift-invariant pointspread function for each wavelength, and a ray-trace method, in which we read in data from Zemax and create a shift-variant set of pointspread functions along with a geometric distortion function. The default optical image has diffraction limited optics. We compute the irradiance field from the scene.

oi = oiCreate;
oi = oiCompute(scene,oi);
oi = oiSet(oi,'name','Small f number');
vcAddAndSelectObject(oi); oiWindow;

Increase the f-number of the optics and compute again.

Increasing the f-number of the optics will blur the irradiance image. The optics structure is attached to the optical image. To increase the f-number we get the optics object, set its f number, and then reattach it to the optical image.

optics  = oiGet(oi,'optics');
fnSmall = opticsGet(optics,'f number');
fnBig   = 3*fnSmall;
optics  = opticsSet(optics,'fNumber',fnBig);
oiBigF  = oiSet(oi,'optics',optics);
oiBigF  = oiCompute(scene,oiBigF);
oiBigF  = oiSet(oiBigF,'name','Big f number');   % Name for the GUI
vcAddAndSelectObject(oiBigF); oiWindow;

Use plotOI to compare the two different optics

In this case we plot the point spread function at 600 nm. First for the small f/#.

% Let's view this wavelength
thisWave = 600;
% Most ISET plotting routines can return the plotted data into a variable
pData = plotOI(oi,'psf',[], thisWave);
set(gca,'xlim',[-20 20],'ylim',[-20 20])
colormap(0.5*gray + 0.5*ones(size(gray)))
title(sprintf('F-number = %d',fnSmall))

% Here are the values returned by plotOI
pData
pData = 

      x: [200x200 double]
      y: [200x200 double]
    psf: [200x200 double]

Show the effect of the larger f/# on the PSF

This is for the larger f/#. We just show a 20 um square region.

plotOI(oiBigF,'psf',[], thisWave);
set(gca,'xlim',[-20 20],'ylim',[-20 20])
colormap(0.5*copper + 0.5*ones(size(copper)))
title(sprintf('F-number = %d',fnBig))

% We can also get the plotted values from the figure
pData = get(gcf,'userdata');
pData
pData = 

      x: [200x200 double]
      y: [200x200 double]
    psf: [200x200 double]

Use plotOI to quantify the optical image

This example plots an RGB representation of the irradiance field in the optical image.

xy = [];        % Irrelevant variable for this plot
gSpacing = 17;  % The grid spacing in microns
plotOI(oi,'irradiance image with grid',xy,gSpacing);
title(sprintf('F-number = %d',fnSmall))

Plot an RGB representation of the new irradiance field

xy = []; gSpacing = 17;
plotOI(oiBigF,'irradiance image with grid',xy,gSpacing);
title(sprintf('Zoomed view: F-number = %d',fnBig))

Now, run using parameters from human optics

The defcous of the human optics is quite surprising. In particular, the blurring of the short wavelength light is very extreme. That is illustrated in this example.

oiHuman     = oiCreate('human');
oiHuman = oiCompute(scene,oiHuman);
oiHuman = oiSet(oiHuman,'name','human optics');
vcAddAndSelectObject(oiHuman); oiWindow;