1.4   Examining pixel values

The grey-scale brightness of the image gives you a good indication of the relative temperature of different areas of the image. However, if you want to know the temperature in the area represented by a particular pixel, you will need something a little more exact. This page shows you how to find the digital value of individual pixels and using it to work out the temperature it of that area. You will work mainly on the image from January 1997, so activate this image window now by clicking on it.

Pixel values on the status bar

To discover the exact value of any pixel, simply point to it with the mouse and click the left mouse button once to move the cursor to that point. The cursor shows as a cross centered on the pixel you clicked on. The [x,y] position of the pixel, and its integer value all show on the right side of the status bar of the Bilko application window (see figure (17K))

Question 1 In the image from January 1997 what are the pixel values and corresponding temperatures in the areas shown below? (Try to avoid pixels next to a land pixel.)
a)   Gulf of Guinea b)   Bay of Bengal c)   North Sea Note: The temperature will vary within each area, so a rough value will do; just point, click and look at the status bar. Use the information from the image description image description to convert from digital value to temperatue in °C.

Cursor moves

So far you have moved your cursor around by clicking your mouse on the image. You can also do this using the arrow keys on the keyboard:

		moves the cursor to the left
		moves the cursor up
		moves the cursor down
		moves the cursor to the right

Question 2
Move the cursor around using the keyboard arrows, noting its [x,y] position on the status bar. How many pixels does the cursor move with each key stroke?
 

You can move the mouse 1 pixel at the time by holding down the control key while using the arrow keys (i.e. [CTRL+],   [CTRL+] etc. )

Finding a pixel with known coordinates

You will now find a pixel in the image Go To function. As most of Bilko's functions this can be accessed in several ways:

From the menu bar:
  - either click on Edit, then Go To on the drop down menu,
  - or hold down the [ALT] key and type E, then type [G]. ( In short [ALT+E] > [G] ).
Mouse shortcut:
  Right-click on the image (depress the right mouse button) and select Go To.
Keyboard shortcut:
  Hold down the [CTRL] key and type G. (In short [CTRL + G ] ).

Any one of these options will open the Go To dialog ( figure (6K) ). This allows you to set the [x,y] position of the pixel you want to find:

1. Enter the [x,y] coordinates into the two Position boxes.
2. Set the Selection Type; to find a single pixel (a point) choose Point Selection using the drop-down arrow to the right of the selection box.
3. Click OK to accept the settings.

Note: The Go To dialog also allows you to set the increment of cursor moves. The Normal box sets the increment for each arrow key stroke (10 by default). The Control box sets the increment for cursor movements made by holding down the control key while using the arrow keys (1 by default).

Pixel coordinates and the zoom function