If not accomplished previously, download a copy of NIH Image (Macintosh) (version 1.62 or later) software either, from the NIH site or the Scion Corp. (PC). If computing on an Window PC the software is only available from Scion Corp. Install the software onto your hard drive and open the program. You must be running Windows 95/98 for this version to work. It was ported from the Macintosh version, and as such, not all features work exactly in the same manner as the Macintosh version.

Click and download the 01191907.tif.sit file ( it will need to be unstuffed/unzipped) from the previous page and open it in the NIH software program (all activities refer to this image). Use the magnifying glass to enlarge the image to a 16:1 ratio. Roll the cursor around the image and view the info box. Reduce the image to a 1:1 ratio.

So that I know you are on the correct "track", use the FORM to send me your answers to the questions below.

1. What information in the Info box keeps changing?
2. As you move the cursor along the same horizontal row (X values), which numbers change?
3. If the cursor is moved up or down the same column (Y values), which numbers change?
4. If the cursor is moved left or right of the horizontal row, does the Y value remain the same?
5. What is the x, y value of the pixel in the lowest left hand region of the image?
6. How many rows does this image contain?
7. How many columns are there in this same image?
8. Based upon the total number of rows and columns how many pixels are in this image? This is the same as if one were to determine the total number of seats at a boxing match. The number of seats is the same as the number of pixels.
9. What are the total number of pixels which make up this image.
10. What is the value (DN) of the pixel located at x= 130 and y= 114?
11. What is the value (DN) of the pixel located at x= 0 and y = 0?
12. Find a very bright (light color) pixel and give me its x,y coordinate and its DN value.
13. Find a very dark color pixel, give me its x,y coordinate and its DN value.

Remember, a digital image is an organized system of numbers which are placed in rows and seats, to which are assigned a color. In turn, this organization produces a recognizable picture.

To the left of all images is the LUT (Look Up Table). This table controls the brightness level of each of the 256 shades of gray which are portrayed by this program. The appearance of the image can be controlled by changing this scale. Place the cursor in the LUT and move it up and down. What do you notice about the pixel values?

Once again, zoom in on the image and choose any pixel. Using the info box, write down its location and gray value (DN). Use your cursor to locate the same DN on the LUT. The color you found on the LUT is the same as the one you located in the image. You are now going to change the LUT by clicking on Options/Color/Tables on the main menu bar. Select the color Fire-1. Again zoom in on the pixel you located earlier and read its value. Has it changed? If the cursor is placed at the same value in the LUT, is the color the same? Try a couple of the of the LUTs and determine if the value (DN) remain the same. By now you should realize that changing the Look Up Table (LUT), does not change the digital value of the pixel - just how it is displayed!

The concepts you've learned in this activity will become very important as you move through the workshop. Another activity, contrast/brightness, will provide you with a grounding in manipulating an image to discover more detail.

Hurricane Opal Project Activity