components.zone.zoneplategenerator

class ZonePlateGenerator(config={}, **kwds)[source]

Bases: Component

Zone plate test pattern generator.

A zone plate (in this context) is a 3 dimensional (horizontal, vertical & temporal) frequency sweep which can be a useful test pattern in image processing applications. BBC R&D Report 1978/23 describes some typical uses. A static circular zone plate (see recipes below) resembles the Fresnel zone plates used in optics.

At first sight there are an alarming number of configuration values, but you normally only need to set three or four of them. I suggest using the pyctools-editor tool to connect a zone plate generator and Qt display, open the generator’s configuration dialog, set looping to repeat and run the network so you can experiment with the settings as you read this documentation.

Each parameter is normalised so a value of 1.0 covers the entire frequency “gamut”. For example, setting kx2 to 1.0 will sweep the entire horizontal frequency range over the width of the picture.

name	controls
`k0`	phase at zero frequency
`kx`	horizontal frequency at x=0 (left hand side of picture)
`ky`	vertical frequency at y=0 (top of picture)
`kt`	temporal frequency at t=0 (start of sequence)
`kx2`	horizontal frequency with x
`kxy`	horizontal frequency with y
`kxt`	horizontal frequency with t
`kyx`	vertical frequency with x
`ky2`	vertical frequency with y
`kyt`	vertical frequency with t
`ktx`	temporal frequency with x
`kty`	temporal frequency with y
`kt2`	temporal frequency with t

Note that these controls are not all independent. For example, kxy and kyx produce the same effect on a square image (and a subtly different effect on non-square images).

Recipes

static circular (or eliptical for non-square images):
```
kx=0.5, kx2 = 1.0, ky=0.5, ky2=1.0
```
static hyperbolic (entire horizontal gamut):
```
kx=0.5, kxy = 1.0, ky=0.5
```
static hyperbolic (entire vertical gamut):
```
kx=0.5, ky=0.5, kyx = 1.0
```
circular at temporal frequency of 1/4 the frame rate:
```
kx=0.5, kx2 = 1.0, ky=0.5, ky2=1.0, kt=0.25
```
all temporal frequencies across width, all vertical frequencies across height:
```
ky=0.5, ky2=1.0, ktx=1.0
```

Comments or questions? Please email jim@jim-easterbrook.me.uk.