JavaScope consists of 19 class files. These class files are placed on a web server running on the same workstation running the SSCd and RCMd emScope daemons. This is necessary as the Java applet can only communicate over the Internet with the machine from which the applet was originally loaded. A basic web page is developed that starts the applet, providing a button that starts the JavaScope application interface. The applet is loaded into a web page with an HTML tag similar to:
<APPLET CODE="JavaScope.class" width=120
Access control can be added to this page to password protect or otherwise restrict access to the Applet. This is the responsibility of the web server configuration.
When the Java Applet is started it connects to the SSCd and RCMd server processes on the host from which the applet was loaded. The applet queries the current state of the microscope and camera and presents this information to the user via the user interface as shown in figure 2.
The left-hand window displays the last image acquired. Several options are available to determine how the image is acquired and transferred to JavaScope.
Transfer: If "compression" is selected, the SSCd compresses the image (JPEG) prior to sending it to JavaScope. Otherwise the data is sent in its full and uncompressed form. When accessing the scope from outside the local area network using the compression option can significantly speed up the image acquisition process with almost no discernable sacrifice in image quality.
Mode: Images can be acquired either singly or in continuous acquire mode. In "single frame" mode the applet updates the image on each press of the "Acquire" button. In "continuous acquire" mode the applet continuously updates the image after the "Start" button is pressed until the "Stop" button is pressed or the acquisition mode is changed. This provides a "live" view from the instrument. At best this will update the image several times a second, in practice it can take several seconds per image over a relatively slow network such as the Internet.
Size, Binning, and Exposure: These control the basic parameters of the CCD camera acquisition process. Exposure is the number of seconds to expose the CCD to the electron beam; binning is the number of CCD elements which make up a pixel, and size is the pixel dimensions of the image to be acquired (after taking binning into account, 128x128 binned by 8 covers the entire 1024x1024 element field of view of the CCD).
The right-hand window displays a basic microscope control panel.
Magnification: Allows the magnification of the TEM to be adjusted to any of the listed values. The intensity of the electron beam is automatically adjusted to account for the change in magnification so as to maintain a consistent average illumination.
Intensity: Allows the intensity of the electron beam to be modified. The units are currently uncalibrated so it takes some trial and error to effect a reasonable change.
Focus: Allows for some control over focus. Manual focus allows free control of the focus to any selected value. The current level of defocus can be measured using the button supplied. If the specimen has some structure, is not too dark and is not too far from focus (<25 um from focus for example) this method returns a reasonable estimate of the current defocus. The autofocus option functions by first measuring the defocus and then changing it to the appropriate value. During measure- or auto-focus procedures, image acquisition is unavailable as the camera is being used to perform the focusing routines on the server.
Goniometer controls: Four buttons are provided to allow the image to be shifted in the directions corresponding to the axes of the acquired image. The size of movement can be selected ranging from a pixel to a full screen. The specimen can also be moved using the left mouse button: clicking this button on a feature of the image will cause that feature to be moved to the center of the field of view.