Change the appearance of imagery

The Raster Layer tab for a raster layer includes essential raster functionality to adjust the display and appearance of imagery. Select a feature layer in the Contents pane to access the Raster Layer tab.

Visibility range

The Visibility Range options allow you to adjust the scale at which raster layers display.

Use the In Beyond and Out Beyond values to limit the visibility of a raster to be between specific scales. Choose from one of the preset options in the drop-down menu or enter a scale in the text box. Click the Clear Limits button to remove the visibility settings.

Effects

The following Effects options allow you to compare two overlapping rasters:

• Transparency slider —Reduce the opacity of the selected raster. This makes the underlying raster visible. The selected raster must be the uppermost layer that is enabled in the Contents pane for you to visualize the transparency.
• Layer Blend—Draw the entire layer and then blend it with the content below it in the drawing order. Each mode performs a type of mathematical calculation on the layer to provide various results, such as drawing topography above background layers but keeping its labels visible.

Compare

The following Compare options allow you to compare two overlapping rasters:

• Swipe tool —Pull back the raster on top to reveal the raster underneath it. To deactivate Swipe, on the Home tab, click the Explore button .
• Flicker button —Turn the selected layer's visibility off and on continuously. The number of milliseconds (thousands of a second) defines the flicker rate. Flicker can be used regardless of the active tool. It stays on until you turn it off, switch to another view, or choose a different layer. Flicker is useful for detecting change in imagery layers, data quality comparison, or other analysis in which you want to see the difference between layers.

Rendering

The Rendering options allow you to control the display of rasters and imagery by adjusting the Symbology, Stretch Type, Dynamic Range Adjustment (DRA), Resampling Type, Band Combination, and Masking options.

The Symbology button is the principal interface for managing the display controls. The lower portion of the button is a drop-down menu that offers you a selection of renderers specific to the type of data you are working with. Click the button to open the Symbology pane, which gives you access to all of the parameters related to setting symbology, such as Stretch Type and Band Combination, including quick access directly from the tab.

The Symbology options are as follows:

• Stretch—Displays values along a color ramp for a single band. If your a has multiple bands, you can select a single band from the Band drop-down list.
• RGB—Displays the raster using a three-band composite in which the bands are shown as red, green, and blue. You can choose which band you want to display for each of the Red, Green, and Blue display bands. An alpha band is also supported, and it acts as a transparency mask, providing a transparency value for each pixel. An alpha band can be turned on or off for multiple-band raster datasets rendered with the RGB renderer.
• Vector Field—Allows you to display phenomena such as currents as arrows, or vectors, where the direction of the arrow indicates the direction of the current, and the size of the arrow is related to the force of the current. Vector Field can be applied to a dataset with a magnitude and direction or a U and V component.

You can control how the range of values is displayed with the Stretch Type button . The lower portion of the button is a drop-down list that allows you to choose the contrast stretching method. Click the button to open the Histogram page in the Symbology pane.

The Stretch options are as follows:

• None—No stretch method will be applied to the layer, even if statistics exist. To display data other than 8-bit data, image values are linearly mapped between 0 and 255. None is a good choice if you want to examine absolute values in your raster datasets.
• Minimum Maximum—Applies a linear stretch based on the output minimum and output maximum pixel values, which are used as the endpoints for the histogram. For example, in an 8-bit dataset, the minimum and maximum values could be 33 and 206. A linear stretch is used to distribute the values across 256 values, from 0 to 255. This increases the ability to see differences in values throughout the dataset. Minimum Maximum is a good choice for standardizing the appearance of multiple rasters for comparison.
• Percent Clip—Cuts off a percentage of the highest and lowest values, and applies a linear stretch to the remaining values across the available dynamic range of the data type. This reduces the effects of outliers and enhances the remaining data.
• Standard Deviation—Applies a linear stretch between the values defined by the standard deviation (n) value. For example, if you define a standard deviation of 2, the values beyond the second standard deviation become 0 or 255, and the remaining values are linearly stretched between 0 and 255.
• Histogram Equalize—Applies a nonlinear contrast stretch where the values are spread out throughout the bit depth range. This method is appropriate when there are many pixel values closely grouped together.
• Histogram Specification—Applies the specified piecewise histogram to display the pixel values. The piecewise histogram allows you to map the input pixel values to a rendered value.
• Custom—Applies the custom stretch, as specified by the histogram settings in the Symbology pane.
• Esri—Uses a modified sigmoid stretch that uses an S curve to find the mean, which helps prevent pixel values from being stretched beyond the maximum value. This method is used to provide a good overall contrast stretch to imagery.

Dynamic range adjustment (DRA) is a feature that automatically adjusts the active stretch type as you navigate around an image based on the pixel values in the current display. You can turn this on or off by clicking the DRA toggle button . The Dynamic range adjustment statistics can be locked to keep them from changing by clicking the Lock Statistics button after the adjustment has been applied.

Alter the image resampling type by using the options in the Resampling Type drop-down list . Nearest Neighbor more closely retains the original pixel values, whereas the other resampling techniques produce a smoother image by interpolating values.

The Resampling Type options are as follows:

• Nearest Neighbor—Assigns the value from the closest pixel. This is appropriate for spectral analysis and classification because it preserves the original pixel values. It is also applied to qualitative data, such as land cover. The trade-off is that you may see artifacts where the realignment of pixels presents a break in the feature. The maximum spatial error is one-half the cell size.
• Bilinear—Interpolates the new value based on a weighted distance average of the four nearest pixels. This is appropriate for continuous datasets, such as imagery and elevation datasets.
• Cubic—Performs a cubic convolution and determines the new value of a pixel based on fitting a smooth curve through the 16 nearest input pixel centers, using a 4-by-4 matrix. This is appropriate for continuous datasets used for visualization purposes. It produces a smooth output with less geometric distortion than Nearest Neighbor resampling, but it may result in the output raster containing values outside the range of the input raster.
• Majority—Assigns the most popular value from the 4-by-4 filter window. This is appropriate for resampling categorical or integer data, such as land use, soil, or forest type. Majority resampling acts as a type of low-pass filter for discrete data, generalizing the data and filtering out anomalous data values.

Band Combination provides popular band combinations for displaying imagery such as natural color and color infrared that highlight vegetation.

If you have a raster product or an image service selected in the Contents pane, you will see all of the band combinations associated with that data in the drop-down menu. Popular band combinations are available depending on sensor type and bands. Hover over the band combination to display the associated band name and number.

You also have the option to create custom band combinations. To do this, select Custom and load the bands you want into each color. When you click Add, you can select them from the drop-down menu.

The Masking button allows you to choose a feature class in the Contents pane to mask out the selected raster. This is helpful if you already have a feature class of the area that needs to be masked out.

Enhancement

Adjust the display of a raster dataset by using the sliders for Brightness , Contrast , and Gamma settings. Move the sliders accordingly, or type the desired values. To reset the sliders, click their respective buttons.