X Image Display (XID)

1.0 Introduction

XID is an X Window System application which allows the user to display, interactively manipulate, and store image and image related information. XID was developed to work in conjunction with the Land Analysis System (LAS), however, there are some limited capabilities to display and manipulate non-LAS images.

XID is built on the X Window System and uses the Motif (version 1.1 or 1.2) widget set for its "look and feel." The building blocks of XID are software oriented, making XID a very portable application. Any UNIX system capable of running X11R4 or X11R5 is capable of running XID.

The disadvantage of a portable, software oriented system is a performance degradation for certain tasks. For example, specialized hardware devices for image display have certain functionality (such as zooming) built into the hardware. This makes these operations very fast and efficient. XID must perform these types of operations in software resulting in a slower response.

Another potential disadvantage of using the X Window System for image display is the limited number of colors available. The user must keep in mind that because a portion of the X Window System color map must be reserved for background colors, foreground colors, border colors, shadow colors, etc., not all the possible colors are available for displaying image data (see below for an alternative). On systems with 8-bit displays, only 200 of the 256 colors are available for displaying image data. On systems with 24-bit displays, approximately 7 of the 8 bits for each red, green and blue band are available for displaying image data. The major effect on the user is that certain mapping operations, such as pseudocoloring, may not work as expected. For example, when displaying a black and white image (with a minimum value of 0 and a maximum value of 255), each individual gray level will NOT have its own color map cell. The resulting side effect is that when the user assigns red to the pixel value 0, pixel value 1 may also become red since it may share the same color map cell. An alternative to this is to select User Preferences from the Setup pulldown menu. This function allows the user to choose either 200 or 256 image colors. By selecting 256 image colors, the user is dedicating a separate color map to the main image window. This will give the user the full range of colors but will also cause a great deal more swapping of color maps.

Following is a list and short description of general XID capabilities.

  1. Image file interfaces.

  2. General image analysis tools.

  3. Additional image views.

  4. General image display capabilities.

  5. Graphics capabilities.

  6. General XID setup functions.

  7. General information.

1.1 User Notes

  1. Functionality that was originally designed into XID but which has not yet been implemented is indicated by the particular option being inactive. An inactive item (button, radio button, etc.) is one which shows as a lighter color than the other items (i.e., grayed out). An option may also be made inactive when it is not appropriate to select that option at a given time. It will be made active when it becomes appropriate.

  2. As a general rule, using the dismiss button to close an XID panel indicates the operation or function will be completed or saved. Selecting the cancel button indicates the operation will be ignored (as if it had never been done).

  3. Also as a general rule, the user should always press enter after typing data into a text field. This signals the XID process that entry has been completed. There are cases in which pressing enter is optional. These exceptions are noted in the documentation.

  4. There are several resources an XID user may wish to set. Listed below are the more commonly used ones.

  5. There are also several command line options the user may specify. These options allow the user to indicate initial placement of the main menu and main image window, to specify an image to initially load, and to display help about these command line options.