<HTML><HEAD><TITLE>Display and Contrast Enhancement</TITLE></HEAD><BODY><h2>Display and Contrast Enhancement</h2><P> <UL><B>QUICK STEPS: Adjusting display and contrast levels <BR></B><LI> Move Contrast slider to desired contrast level<LI> Move Brightness slider to desired light level if needed<LI> See section on <A HREF="#Other Ways to Enhance Contrast"> Other Ways to Enhance Contrast</A> if desired<LI> See section on <A HREF="#Working with False Colors"> Working with False Colors</A> if desired</UL><BR><P><P><P>When Viking Images are opened the contrast in the image is low as in the Figure 1 below.<P><BR><IMG SRC="GIFPics/Contrast/APnoCont.GIF"> <P><BR>When images are not pre-scaled for display, the contrast and brightness need to be adjusted. This can be done in a variety of ways, such as dragging the sliders in the Map window, or invoking the <CITE>Process - Enhance Contrast </CITE> or <CITE>Process - Equalize </CITE> commands. However, what seems to work best at least for the MDIMs is to just use the slider in the MAP window to increase the contrast. This next figure is the result of manually increasing the contrast using the contrast slider in the MAP window.<p><BR><IMG SRC="GIFPics/Contrast/APmanC.GIF"><P><BR><h2><A NAME="Other Ways to Enhance Contrast"> Other Ways to Enhance Contrast</A> </h2><P>The contrast in the image below was changed using the <CITE> Enhance Contrast </CITE> command in the Process menu. The ordinary linear contrast enhancement uses the full available brightness range (0 - 255) to display the image. Note that when the enhancement was done, the LUT and Map windows changed also. However, because MDIMS have already been processed significantly, invoking the Enhance Contrast command can sometimes produce extreme results. In the example below, using the Enhance Contrast command resulted in a "washed out" appearance to the image. <BR><P><IMG SRC="GIFPics/Contrast/APenhanC.GIF"><P><BR>A more severe enhancement is performed using the <CITE>Process - Equalize</CITE>command. Generally, this enhancement is not appropriate for use with the MDIMs (see example below) since these images have already been extensively processed, although this method is often used in <A href="Raw.htm">processing the "raw" image files</A>. Equalization divides the pixels of the image as evenly as possible among all the brightness intervals. In other words, each gray level is used to display about the same number of pixels. This has the effect of bringing out detail in the background or larger areas of the image, while losing contrast in the small features. <BR><P><IMG SRC="GIFPics/Contrast/APequal.GIF"><BR><P><h2><A NAME="Working with False Colors" >Working with False Colors</A> </h2><P>Another enhancement procedure that can bring out details in an image is the use of false color. False color look up tables (LUTs) can be accessed using <CITE>Options - Color Tables </CITE> command. The LUT used in the example below is Fire-1, also called a thermal scale, and is one of the most intuitive false color scales. Try other LUTs and note how each bring out different details in the image.<p><BR><IMG SRC="GIFPics/Contrast/APColF1.GIF><P><BR>The "Spectrum" LUT was used in the image below. Note how this LUT brings out subtle variations or details in the landsurface of this image. These variations reflect compositional or textural changes in the surface, the presence of shadows, or changes in slope. For example, some color variations may represent the presence of soil and bedrock exposed at the surface, such as ash or wind blown deposits covering lava flows in some areas, while lava flows in other regions of the image may be free of such mantle deposits. Other color variations may correspond to changes in the actual rock type and soil composition or changes in slope of the landsurface.<BR><P><IMG SRC="GIFPics/Contrast/APfCSpec.GIF"><BR><P><hr>
