TIFF, PICT, PICS (for a stack of images) and a few other file formats are directly read and displayed using the File - Open command within NIH Image. Raw data (images without any encoding or header information) can also be read with the < CITE>File - Import command. However, Viking Image Files are in the Planetary Data System (PDS) format (.img or .imq extensions) and cannot be opened directly using the File - Open command. Instead you must use ACQUIRE-P DS to read a Viking Image file. The PDS "plug-in" that is required for this command to work is already installed in the "Plug-Ins" folder within the Image1.60 folder on this CD-ROM. If you download a new version of NIH-Image, you will need to copy the PDS plug-in to the "Plug-Ins" folder of the new program.
Now you can choose the image file you want to open. These image files are located in the VOImages folder.
As you move the cursor over the image window, note that the coordinates and pixel values for the cursor position are displayed in the Info window. To set the coordinates so that the actual X and Y distances on the images are shown in kilometers, see th e How to Measure Distances and Areas of Landforms on an Image section of this tutorial. The LUT (Look-Up Table) window displays the current gray level or color look-up table. Move the cursor over the LUT window a nd observe that the pixel values are displayed in the Info window (255 or black at the bottom, and 0 or white at the top as the default, or 0 or black at the bottom and 255 or white at the top with the pixel values inverted - see above).
Use the balloon help once in NIH Image to see a description of the image processing tools.
The Viking Images look "washed out" when opened. The next section shows you how to bring out details by adjusting the brightness and contrast levels of the images