Enhancing rasters based on the values in the display

To see features in some images or raster datasets, or to distinguish them more easily from the surroundings, you may want to alter the stretch applied to the histogram. In many cases, you can get the enhancement you need by stretching based only on the pixel values within the display and not using all the pixels in the raster dataset. This is a dynamic range adjustment (DRA).

There are two ways to apply this in ArcMap:

• The first method is by checking the DRA option in the Image Analysis window.
• The second method is by enabling a setting on the Layer Properties dialog box, which is described in the steps below.

Once you choose this option, you can pan and zoom around the image, and the stretch is adjusted based on the pixel values within the display.

This option is particularly useful when you've zoomed into an area where the color range is not as diverse as the entire image, such as an area with a lot of snow cover or buildings with shadows.

Steps:

1. In ArcMap, zoom in to an area of your raster dataset where you want to enhance the visual contrast.
2. In the table of contents, right-click the raster layer and click Properties.
3. Click the Symbology tab.
4. Click either the Stretched or RGB Composite renderer.
5. Click the Statistics drop-down arrow and click From The Current Display Extent.
6. Click OK.