Image Display Functional Requirements

Software Requirements

Overview

These general rules apply:

• control of the display will be by GUI inputs (ie, graphical buttons, text boxes) and/or mouse;
• mouse button functions will be continuously updated/displayed;
• default parameters should be accessible for user modification and resetting to nominal values.

Built-in analysis functions are described under Quick-Look Requirements.

Nomenclature

An image plane refers to a section of the effective video memory which is treated as a single image. Blinking alternates between image planes.

An autoscaling algorithm will automatically compute limits (and potentially the form) of the transfer function.

Specific Requirements

• Full-image display of 8K x 8K mosaic at reasonable compression level. Image should be compressed and/or subsampled in such a way that the object information is not strongly modified -- that is, stars should all appear at close to their relative brightnesses. Both 1K x 1K and 2K x 2K display formats should be supported, at 8x and 4x compression/subsampling respectively.
• "Work display:" Display at least one area at full pixel (or zoomed) scale. The selected region must be graphically marked on the full image (above).
• Images should be displayed in real-time as they are received from the detector ("raw"). There should should be a user override option to defeat or delay this automatic display (note: this does not affect the read-out process). Images stored on disk can also be called back for display.
• There should be an option to gracefully interrupt (ie, terminate) the "loading" of an image. This applies either to the reading of an image from disk into memory or application of the transfer function to an image already in memory. (This does not affect CCD read-out.)
• There should be a erase option, to clear the display before loading a new image.
• Mouse-driven cursor must be able to travel between the two display monitors.
• Incremental movements of the cursor can also be made by keystrokes (eg, arrow keys) in whole pixel units.
• Pixel coordinates and true pixel DN values should be accessible from both the full-screen and "work" displays, via a continuously-updated display of the mouse cursor position. The default coordinate system displayed will be that necessary for accessing a given pixel with other tools (eg. IRAF implot, imstatistics or epix tasks). Other coordinate systems (eg, x,y pixels; chip,x,y pixels; RA and Dec) should be user-selectible (see Quick-Look Requirements). Also, whole pixel or fractional pixel readouts should be a user option.
• For display of "raw" images, saturated pixels should be flagged (eg, set to specific color).
• It is a desirable option that CCD defects can be similarly flagged.
• An optional zoom box (saoimage-style), including a marker for the central pixel, is desirable.
• Blink capability between at least two (preferably four) image planes. If three or more planes, the user can select which planes are to be blinked, and the order (forward or reverse). Blinking will be under the control of a mouse button click or keystroke.
• User can optionally "lock" 2 or more planes together for purposes of panning and zooming (ie, spatial registration). User can also lock the lookup tables for two or more planes. (These options are extremely useful for blinking.)
• Standard functions:
  • optional pseudo color-mapping;
  • mouse-driven LUT control;
  • mouse-driven panning;
  • mouse-driven zooming (with user-selectible zoom factors);
  • transfer functions will include linear, log, gamma and other (TBD) forms.
  Note that graphical overlays must follow the image during pan/zoom.
• Intelligent autoscaling computation of the transfer function, which may require knowledge of the image type to avoid regions of no interest. For example, a direct image should ignore the "shadowed" regions of the chip in deciding on grayscale mapping. Similarly, for a direct image through a slitmask, only the illuminated regions should be considered. (Some form of histogram equilization is suggested as the most appropriate autoscaling algorithm for the transfer function.)
• Other transfer function options should be:
  • fix the transfer function limits at current or user specified values;
  • limit computation of autoscale transfer function to a user-specified region;
  • automatically adjust the transfer function of one image to match the appearance of another image already displayed (see Design Notes).
• An interactive, fast selection of transfer-function limits is under investigation (see Design Notes).
• The user should be able to select (via mouse clicks) one or many small regions (of adjustable size) which are then mosaiqued or tiled. This is useful for examining, eg. PSFs across the field. Another use would be displaying focus sequences side-by-side. This tiling should occur for all locked planes The size/shape of the box will be determined by dragging out the desired box on the screen. (Note that this is a display option, completely separate from multi-subraster readout of the CCDs.)
• For the slitmask alignment sequence, all alignment stars should be displayed simultaneously, with residual vectors overplotted. (See mask alignment procedure.)
• We should have the capability of removing variations in chip-to-chip gain and bias levels.
• We will need graphics overlay planes both for individual image planes and globally (ie, for graphics which are to appear for all image planes).
• Hardcopy of either display screen, with filename/user/time/date stamp.

Design Notes

The highly-interactive limits selection would be chosen by another button. In this case, the user drags out a box around the image region of interest. This selected region is then reloaded into video memory with a transfer function running from the minimum to maximum intensity encompassed by the box, and the LUT is reset to full ramp. The user will then adjust the LUT (via standard mouse control) to bracket the intensities of interest. When ready, the user selects this range (either by another mouse button or a graphical button), and the LUT ramp is mapped backwards to estimate the min and max value of interest to the user. These values become the new transfer function limits, the boxed region is redisplayed (using the new limits) and the LUT ramp is reset to full range. This procedure is repeated until the user selects the "redisplay" button, when the (final) transfer function limits are applied to the entire image. Note that an "undo" option, to reverse the last change, will probably be required.

Hardware Requirements

8-bit display grayscales or colors are probably adequate, but we should allow for the possibility of 24-bit display.

Three (?) button mouse.

Lots of memory (TBD).