8: Image Display and Quick Look software

8.1: Introduction

During normal operation of DEIMOS the CCD exposure will terminate, the CCD mosaic will readout its data, and the resulting image will be displayed on the observer's screen. The appearance of the image will be different for direct, spectral, and alignment images. The observer will inspect the raw image looking for technical flaws and scientific content. Another observer may be using an adjacent workstation to monitor and modify the pipeline data analysis while looking at extracted spectra or performing astrometry. These activities require a convenient means of interacting with an 8k x 8k mosaicked CCD image.

DEIMOS appears to be among the first of the astronomical projects with large format mosaicked CCDs. University of Hawaii already has a detector much like that of DEIMOS, and there are plans for similar systems at NOAO, CfA, and University of Texas. There are no existing image display clients which handle mosaic geometries in a self-contained fashion. Chapter 7 has outlined some of the protocols which will be needed in order to support the requirements of this chapter.

In this chapter are detailed requirements for the image display and the quick look analysis tool. The requirements have been written from both technical and scientific standpoints. Also included are the results of preliminary investigations into the availability of various hardware and software components.

8.2: Figures


8.3: Glossary

Cosmic ray. An atypically bright cluster of adjacent pixels caused when cosmic ray deposits charge in the detector.
Data Acquisition System. The components involved in CCD readout as described in Chapter 6.
digital number. A raw pixel value as read from a CCD and expressed as an integer.
The Flexible Image Transport System. This is the IAU-endorsed standard scheme for astronomical data interchange. It is defined by a series of papers which have appeared in Astronomy and Astrophysics Supplement. It is not related to any particular implementation in code.
Full width at half maximum. A measure of the width of a feature in an image.
A graphical user interface.
Look Up Table. A construct in video display hardware that maps from pixel values to color levels.
Institute of Electrical and Electronics Engineers. In this chapter it refers to a format for storing floating point numbers which is used by the FITS standard and most modern computing hardware. The format is specified in document IEEE 754.
Point Spread Function.
World Coordinate System. A mapping from pixel coordinates to positions on the sky (or, in the case of DEIMOS, the slitmask).
The X11-based image display client that NOAO has developed for use with IRAF.
SAOImage, the Next Generation. The image display client from SAO. It incorporates elements from NOAO and Tk/Tcl.
The ESO Real Time Display. A Tk/Tcl-based tool which monitors the continuous receipt of images as might be provided by a guide camera.
The image display client currently used by Keck I instruments.
An X-server based mechanism for interclient communication.
Random Access Memory
Redundant Arrays of Inexpensive Disks. A technology which combines many separate, relatively slow and small disks into a device which appears to be a single, large, fast disk.
Asynchronous Transfer Mode. A high-bandwidth data transfer technology for networking. Initial implementations provide rates of 155 Mbits/s, but the vendors promise increases of more than a factor of ten.
Small Computer Systems Interface. Probably the most common means of communication between CPU and peripheral devices such as disks and tape drives. The original SCSI bus has a 2 Mbyte/s transfer rate, but later improvements have increased this to as much as 40 Mbyte/s.
Peripheral Connect Interface. A newer bus standard now being employed in PCs and workstations.
An older bus standard which is used by several large format display interfaces.
Tool Command Language and its GUI counterpart. A freely redistributable software environment used to construct automated processing tools and GUIs.
High Definition TV. A new standard for consumer TV which will use displays of approximately 2k x 1k pixels.
The separation in memory between adjacent pixels in adjacent rows of the image. Adjacent pixels in the same row will typically be contiguous. Adjacent pixels in adjacent rows must stride past all the other pixels in the row. Because DEIMOS will mosaic the images in memory the stride will be larger than the case where the images are not mosaicked in memory.

Steve Allen <sla@ucolick.org>
$Date: 1996/03/19 06:07:00 $