2G

G) Display Settings Tool
In this 2:48 video, Chris tells us a little about why we want to use a program like Afterglow Access:
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BRIEF TOUR of the “DISPLAY SETTINGS” TOOL
1. Open Afterglow Access (AgA) if you do not already have it open. Either use ctrl tab# to switch between screens, or arrange AgA and the instructions side by side.
2. Open one of the sample files (images), or your own image in AgA.
3. The “Display Settings” window on the workbench opens automatically when you open a file: This is the top button of the column on the far right.
– The Display Settings appear immediately to the left of the right hand column tools.
– If you want these settings to fill your screen for easier viewing, press the / (slash) on your keyboard. Pressing the . (period) will fill the window with the image you have loaded, pressing the , (comma) will make the library file on the left fill the window, and the Esc button on your keyboard returns all three panels together on the workbench – the library on the left, the image viewer (or viewport) in the center, and the tool settings on the right.
4. Return your attention to the Display Settings panel. For now, ignore the graph in the middle of this panel.
5. Above and under the graph are many different settings. Pick at least eight to explore.
Do you remember what a “count” is? At the beginning of this Exploration, we did an exercise with a poster that modeled a CCD camera. Recall, electromagnetic radiation, which is how we get almost all information from space, is modeled as a wave when it travels and as a particle (photon) when it interacts with matter. The photons are what interacts with the pixels in the CCD camera. The camera, and then the computer, records the information for each pixel as “counts”, which roughly corresponds to the number of photons gathered in each pixel.
All the settings for the Display panel really manage how the “counts” stored on the computer are displayed, but they don’t change the actual counts in each pixel. The pixel values are only changed during bias, dark, and flat calibrations. We do not have to worry about these calibrations, it is done for us by Skynet when it performs your image request.
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JOURNAL WORK:
1. Make a list of the eight settings you examined.
2. Write down a few words for each setting as to how, if at all, it changes the image.
3. Before moving on to the next setting, spend a few minutes discussing how it could be explained or improved for a BVI person. Enter a brief description into the Journal.
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JOURNAL BOX
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ACTIVITY: The Histogram
Now return to the graph on the Display Settings panel.
The histogram (graph) shown can be modeled with an egg crate and glass gems. Recall from math class that a histogram is a frequency chart (if you don’t remember what that is, it will be explored in detail in this activity).
LEADERS/TEACHERS: The following link includes two things: 1) Instructions for making the histogram, and 2) Information on the Prompt6 telescope in Chile. Reminder: the leader Resources for Section 2 also have the answers to the Journal questions.
JOURNAL WORK
– After you have completed the activity, use the same Journal Box you used ABOVE to answer these questions:

1. The histogram on Afterglow Access and your egg crate histogram use the same variable (think about the “unit” used) for the x-axis. What is this variable? Now look at the y-axis. What is the variable on the y-axis?
2. For your egg crate histogram, what is the highest POSSIBLE “y” value? Carefully look at Afterglow Access for the scale it shows. What number does the egg crate histogram correspond to on the Afterglow Access histogram?
3. For your egg crate histogram, what is the highest POSSIBLE “x” value? What number does this correspond to on the Afterglow Access histogram?
4. What, if anything, happens to the histogram on AgA when you change the settings labeled “Background Level Percentile” and “Saturation Level Percentile”?
– Do the changes affect the image in the middle viewer panel?
5. The graph has two red vertical lines. Which settings change where the red vertical lines are? Do you have a guess as to what the meaning is?
6. Which of the settings gives the largest number of pixels with the lowest number of counts?
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In the next part we will gain some experience in the Quorum programming language. A matrix will serve as our model of the data array (image) stored in the computer.

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