1. Introduction to FESTIVAL | 2. The interface | 3. Hardware requirements

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1.3 Data handling

An image undergoes the following operations before it is displayed in the visualization GUI:

  1. Preping: call to the appropriate SSW routine, eit_prep, secchi_prep, etc. This includes reading the corresponding FITS file.
  2. Rotation: rotation to solar north up or ecliptic north up, depending upon the choices made in projection GUI .
  3. Filtering: apply the user defined sequence of filters, if any.
  4. Difference: subtraction of the previous image of the same instrument if in running difference mode. If the previous image is not already present in memory, it is requested and follows steps 1 to 3.
  5. Enhancement: conversion from 16 bits to 8 bits according to the parameters defined in the enhancement GUI.
  6. Projection: mapping of the data on the sky according to the settings defined in the projection GUI.
  7. Storing in the history stack.

After an image is displayed, FESTIVAL stores in the history stack the 16 bits filtered image, the 8 bits projected image and detailed informations about its processing through steps 1 to 7. Any modification by the user (except panning and zooming) of the scene rendered in the visualization GUI leads to a request for new data. This includes modifying the rotation, filter sequence, enhancement parameters, projection type, etc. When a new data is requested, FESTIVAL looks up the history stack for a previously processed data that has all the right properties: roll, filter sequence, enhancement parameters, projection type, etc. If it is found, the projected image is displayed instantaneously. If not, FESTIVAL will find the data closest to what is requested. For example, if the user displayed an image and then changes the projection type, a data that is correctly filtered is already present in memory. In this case, FESTIVAL does not process the data from scratch (step 1), but uses the existing information and proceeds directly to step 4, and the resulting new data is itself pushed to the history stack. The history stack is a FIFO. Its default size is 300 MB but if your computer has enough RAM, you can increase this value to let FESTIVAL store more data in memory and make it run faster. The size in MBytes can be modified in the system options GUI. You'll then need to restart IDL and FESTIVAL.

Special SECCHI preping options

It is possible to precisely control the way FESTIVAL uses the scc_read_summary and secchi_prep functions to search for SECCHI data and prep the images using a keywords.txt file located in the FESTIVAL_PROJECT/config/ directory. This file has two sections, one for [SCC_READ_SUMMARY] options, one for [SECCHI_PREP] options. Each available keyword for these two functions can be individually controlled in this file. In the example below, we tell scc_read_summary to check for bad images but not for debris, to use the images masks and to remove saturated columns in HI images.

[SCC_READ_SUMMARY]
CHECK=1
DEBRIS=0
[SECCHI_PREP]
SMASK_ON=1
SATU=-1

In the future, this mechanism will be extended to other instruments.

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