A Julia interface to Andor cameras

This Julia package implements an interface to some Andor cameras via the Andor Software Development Kit (SDK). As of version 3.13 of the SDK, the Neo, Zyla, Apogee and iStar-SCMOS Andor cameras should be supported. The AndorCameras package has been tested on under Linux on the Zyla (USB-3 connected) camera, I am interested in feedback about other models.

This document describes:

• the standard interface which implements all the methods specified by the ScientificCameras interface;

• the advanced interface which provides access to all Andor cameras features and commands;

• the installation of the AndorCameras package.

Standard interface

To use the AndorCameras package, just write:

using AndorCameras

which provides all the methods specified by the ScientificCameras interface. This interface is fully documented here and summarized below.

You may also want to:

using AndorCameras.Features

to use the advanced interface.

Open and close a camera

To open an Andor camera:

cam = open(AndorCameras.Camera, dev)

with dev the device number (0 is the first device). To figure out how many Andor devices are available:

AndorCameras.getnumberofdevices()

To disconnect a camera from the hardware:

close(cam)

Note that this is automatically done when the camera instance is claimed by the garbage collector.

Configure a camera

Region of interest

A region of interest (ROI) may be selected by:

setroi!(cam, [[xsub, ysub,] xoff, yoff,] width, height)

where xsub and ysub are the dimensions of the macro-pixels (in pixels and both assumed to be 1 if not specified), xoff and yoff are the offsets of the ROI relative to the sensor (in pixels and both assumed to be 0 if not specified), width and height are the dimensions of the ROI (in macro-pixels).

Macro-pixels are blocks of xsub by ysub pixels when rebinning the pixels of the sensor.

In the Andor SDK documentation, the rebinning features are AOIHBin and AOIVBin, the offsets (plus one) are AOILeft and AOITop and the dimensions of the ROI are AOIWidth and AOIHeight.

To query the current ROI call:

roi = getroi(cam)

and to reset the ROI to use the full sensor with no rebinning, call:

resetroi!(cam)

The full dimensions (in pixels) of the sensor are retrieved by:

fullwidth = getfullwidth(cam)
fullheight = getfullheight(cam)

or by:

fullwidth, fullheight = getfullsize(cam)

Frame rate and exposure time

The setspeed! method let you choose the frame rate (fps in Hz) and the exposure time (exp in seconds) for the captured images:

setspeed!(cam, fps, exp)

To retrieve the actual values of these parameters:

fps, exp = getspeed(cam)

Acquire a sequence of images

To acquire a single image (with the current settings):

img = read(cam)

which yield an image in the form of a 2D Julia array. To acquire a sequence of n images:

imgs = read(cam, n)

which yields a vector of images: imgs[1], imgs[2], ..., imgs[n]. The returned images are Julia 2D arrays of same dimensions as the selected region of interest (ROI) and whose element type is derived from the pixel format of the camera as given by:

getcapturebitstype(cam)

You may specify another element type, say T, for the acquired images:

img = read(cam, T)

or

imgs = read(cam, T, n)

but there may be restrictions.

The read methods have the following keywords:

• Use keyword skip to specify a number of images to skip.

• Use keyword timeout to specify the maximum amount of time (in seconds) to wait for acquisition to complete. If acquisition takes longer than this time, a ScientificCameras.TimeoutError is thrown unless keyword truncate is true (see below). The default timeout is computed from the acquisition rate and the total number of images.

• When reading a sequence of images, keyword truncate may be set true to print a warning and return a truncated sequence instead of throwing an exception in case of timeout.

• Keyword quiet can be set true to suppress the printing of warning messages (see above).

Continuous acquisition of images

Continuous acquisition (and processing) of images is typically done by:

start(cam, nbufs) # start continuous acquisition with `nbufs` cyclic buffers
while ! finished()
    img, ticks = wait(cam, sec) # wait for next image, not longer than `sec` seconds
    ... # process the image
    release(cam) # release the processed image
end
stop(cam)  # stop acquisition

where it is assumed that finished() returns true when to stop and false otherwise. Above, img is a 2D Julia array with the last captured image and ticks is the corresponding timestamp in seconds. Releasing the captured image with release(cam) when it has been processed is intended to recycle the image buffer for another acquisition. When the returned image is independent from the corresponding capture buffer, release(cam) does nothing. It is nevertheless good practice to call this method when the captured image is no longer needed because the code is more likely to work with no changes with another camera.

You may specify another element type, say T, for the captured images:

start(cam, T, nbufs)

Advanced interface

This section describes advanced use of the interface to Andor cameras provided by the AndorCameras module. This may be useful to perform specific configuration or actions not covered by the general interface. Dealing with all the features of Andor cameras is greatly simplified by the provided Julia interface.

Constants

The constants defined in atcore.h are available in Julia, for instance AndorCameras.AT_SUCCESS. All constants are prefixed with AT_ and may be imported by:

using AndorCameras.Constants

so that you just have to write AT_SUCCESS instead of AndorCameras.AT_SUCCESS.

Features

Andor cameras have features whose value can be retrieved or set using the array index syntax:

cam[key]
cam[key] = val

where cam is the camera instance, key is the considered feature and val its value. Here key can be something like AndorCameras.SensorWidth or just SensorWidth if you have imported all defined features by:

using AndorCameras.Features

For instance:

using AndorCameras.Features
sensorwidth = cam[SensorWidth]
sensorheight = cam[SensorHeight]

yields the full dimensions of the sensor of camera cam.

The names of the constants defining the existing features closely follow the Andor Software Development Kit documentation. This documentation should be consulted to figure out the supported features and their meaning. If specific features are missing, it is easy to define new ones.

Julia AndorCameras module takes care of the different kind of features depending on the type of their values: integer, floating-point, string, boolean or enumerated. Enumerated features can take integer or string values, they are described below. There are also command features which have no value but are used to send commands to the camera.

To query whether a specific feature is implemented, or whether it is readable, writable or read-only, do one of:

isimplemented(cam, key)
isreadable(cam, key)
iswritable(cam, key)
isreadonly(cam, key)

Integer and floating-point features may have restrictions on the allowed range of values. The minimum and maximum allowed values can be retrieved by:

minimum(cam, key)
maximum(cam, key)

String representation

A string representation of feature key is obtained by:

repr(key)

Enumerated features

An enumerated feature can only have a limited number of predefined values. These values can be set by an integer index or by their name. Assuming cam is the camera instance:

cam[key] = idx

or:

cam[key] = str

with key the enumerated feature, e.g. PixelEncoding, idx and str the index and the name of the chosen value. The following expression:

cam[key]

yields the current index of the enumerated feature. Note that enumeration indices start at 1 (as do indices in Julia). The minimum and maximum indices are respectively given by:

minimum(cam, key)
maximum(cam, key)

the former always yields 1 for an enumerated feature.

To retrieve the string representation of the value an enumerated feature, do one of:

repr(cam, key)
repr(cam, key, idx)

which respectively yield the string representation of the current value of the enumerated feature and of the value at a given index.

To query whether a given index is available or implemented for an enumerated feature, call respectively:

isavailable(cam, key, idx)
isimplemented(cam, key, idx)

Commands

Command features (e.g. AcquisitionStart) are used to identify a specific command to send to the camera. These features have no values. To send the commmand cmd to the camera cam, you just have to:

send(cam, cmd)

Define new features

If specific features are not predefined by the AndorCameras package, you may define them at run-time provided their name and type is known. For instance:

boolkey = AndorCameras.BooleanFeature("SomeBooleanFeature")
intkey = AndorCameras.IntegerFeature("SomeIntegerFeature")
enumkey = AndorCameras.EnumeratedFeature("SomeEnumeratedFeature")
fltkey = AndorCameras.FloatingPointFeature("SomeFloatingPointFeature")
strkey = AndorCameras.StringFeature("SomeStringFeature")

would define 5 features of 5 different types given their names. These features can be used as any others. For instance:

cam[boolkey] = false

If performance and readability are not an issue, a feature may be defined on the fly. For instance:

cam[AndorCameras.BooleanFeature("SomeBooleanFeature")] = false

Installation

The easiest way to install AndorCameras is via the Julia registry EmmtRegistry:

using Pkg
pkg"registry add https://github.com/emmt/EmmtRegistry"
pkg"add AndorCameras"
pkg"build AndorCameras"

The build process assumes that Andor Software Development Kit (SDK) has been installed in the usual directory /usr/local/andor for Linux or C:/Program Files/AndorSDK3 for Windows (read the end of this section if you have installed the SDK elsewhere).

If Andor SDK is not installed in the usual directory, you can define the AT_DIR, AT_INCDIR and/or AT_LIBDIR environment variables before building AndorCameras. These variables are used as follows:

• AT_DIR is the directory where the Andor SDK has been installed. If this environment variable is not defined, it is assumed to be /usr/local/andor for Linux or C:/Program Files/AndorSDK3 for Windows.

• AT_INCDIR is the directory containing the Andor SDK header file atcore.h. If this environment variable is not defined, the header file is searched in directories $AT_DIR/include and $AT_DIR (in that order).

• AT_LIBDIR is the directory containing the Andor SDK library (libatcore.so on Linux, atcore.dll on Windows). If this environment variable is not defined, the library is searched in directories $AT_DIR/lib and $AT_DIR (in that order).

For instance id Andor SDK has been installed in /opt/andor, you can define the AT_DIR environment variable in Julia by:

ENV["AT_DIR"] = "/opt/andor"

before building AndorCamera:

using Pkg
pkg"build AndorCameras"