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Change the symbology of imagery

Depending on the type of imagery you are working with, you will have a number of options in terms of how you display or symbolize it. Only the types of symbology that are valid for the data you have selected will be presented. For example, multispectral imagery can display using a three-band color composite—also known as an RGB composite—where you use the different bands available to you to highlight features of interest. You can also display the values along a color scheme to show which areas are brighter than others. This is also referred to as applying a stretch to a dataset. Classify and Discrete can be used to group continuos data into a limited number of groups. Vector Field allows you to display ocean and wind currents as arrows indicating magnitude and direction. This will also work with any dataset that has a U and V component.

Modify the appearance

  1. From the Appearance tab, click the top half of the Symbology button.

    Symbology button

    The Symbology pane appears. From here, you can set all of the symbology parameters. Clicking the bottom half of the Symbology button gives you quick access to different symbology options.

From here, you can fine-tune the parameters specific to the symbology type you have selected. You can also select other layers from the Contents pane and, without closing the Symbology pane, you can apply the same symbology to them.

There are subtle, yet distinct differences between the options you have when symbolizing imagery. RGB, Unique Values, Stretch, Colormap, Classify, and Discrete all accomplish similar things but in different ways. Stretch is the classic color scheme option; it takes all the values in your data and stretches the range so it fits on a range. For example, 8-bit data will be stretched from 0 to 255. Unique Values is similar, except the colors are not continuous. This is appropriate for qualitative data such as land cover. A discrete color scheme is continuous, like stretch is, but you decide how many colors it should use to display your data with no legend within the Contents pane. It then groups the values of pixels together accordingly. Classify is similar to Discrete, except it looks at the distribution of values and groups the values into the number of breaks or colors you want to display. A color map is useful when you want to select a color for each pixel value. These can be saved, imported, and exported for use on other datasets. 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 any dataset with a magnitude and direction or a U and V component.

Save symbology settings as a template

You can save the symbology settings of your choice as a template from the Symbology pane and reuse them as custom functions that can be applied from the Raster Functions pane. This generates a template that contains the appropriate functions to replicate the symbology used to display the layer of a raster dataset, mosaic dataset, or image service. This item has several uses:

  • Use it as a processing template for a mosaic dataset. Open the Raster Type properties, click the Functions tab, right-click a Processing Template, and click Load.
  • Edit the function chain in a mosaic dataset or its items using the Edit Function Chain option in the layer context menu.

These are the steps to save a template of symbology settings as a function that can be accessed from the Raster Functions pane.

  1. Add a raster dataset, mosaic dataset, or image service to a map.
  2. Click the Symbology button on the Appearance tab.
  3. Modify the symbology, such as applying a stretch or using a different color scheme.
  4. Click on the Options menu Menu in the Symbology pane and select Export as raster function template.
  5. Provide a name for the template.
  6. Select the Custom Category and Sub-Category.
  7. Provide Description and Type and click OK.

RGB

RGB stands for Red, Green, and Blue and enables you to create composite images by loading different multispectral bands into each of these channels. Under Band Combinations, select which bands you want to display as red, green, and blue. To obtain a natural-looking image, match the red with the red, green with green, and blue with blue. You can also create other composites that highlight how features respond to different parts of the electromagnetic spectrum. For example, load the near infrared band into the red drop-down list, the red band into the green drop-down list, and the green band into the blue drop-down list. This creates a composite that uses the strong reflection of vegetation in the near infrared band and displays areas of high vegetation as red.

Symbology RGB

If you want to set the background value, you need to do so for each band. Although these values are often the same for each band, it is possible that they would change. Check the Display background value and input the values that represent the background and choose the color for the background. You can also choose a color for NoData.

Use Stretch Type to define the range of values you want to display. This is often used to eliminate extreme high and low values that represent noise in imagery. When you select one of these options from the Stretch Type drop-down list, it uses the parameters that you set here. There are five possible Stretch Type options:

  • None displays the values on a scale from the potential minimum and maximum values. For example, if the dataset is 8-bit, the values would be stretched from 0 to 255, regardless of the actual distribution of pixel values. None is a good choice if you will be examining multiple rasters and want to standardize the display.
  • Minimum Maximum displays the values on a scale from the actual minimum and maximum values. For example, if the dataset is 8-bit but the values range from 20 to 225, the display is stretched from 0 to 255. This increases the ability to see differences in values throughout the dataset.
  • Percent Clip cuts off a percentage of the highest and lowest values. This reduces the effects of outliers in the datasets.
  • Standard Deviation displays the values between a specified number of standard deviations.
  • Esri is based on a sigmoidal stretch, which makes it ideal for maintaining contrast in bright areas, such as an urban area surrounded by a desert.

Adjust the Gamma of your imagery to highlight the contrast of moderate pixel values.

Statistics are used to determine how to display the data. In the Statistics drop-down menu, there are options for DRA, Dataset, and Custom.

When DRA is chosen, the statistics based on the current display extent are calculated as you zoom and pan around the image. Dataset calculates the statistics for the entire dataset and uses those values no matter where you are in the image. You also have the option to input your own statistics in the table, using the Custom option. You can do this manually by importing the statistics from another dataset or by importing an .xml file from the Options menu. When finished, you have the option to save your custom statistics.

RGB options

You can access these options from the Menu button at the top of the Symbology pane.

You have the option to import a layer or package to set the parameters.

You can save your current symbology as a raster function template.

Unique Values

Unique Values randomly assigns a color to each value in your dataset. This is often used with thematic data, such as land cover, because of its limited number of categories. It can also be used with continuous data if you choose a color scheme that is a gradient.

Symbology Unique Values

Unique Values options

You can access these options from the Menu button at the top of the Symbology pane.

You have the option to import a layer file, a package, or a color map to set the parameters.

You can also export your settings as a color map so it can be applied to other datasets.

You can save your current symbology as a raster function template.

Under the Advanced tab, you can format the labels of category names. As you make changes here, they will be updated immediately in the Contents pane.

Stretch

Stretch allows you to define the range of values to be displayed and applies a color ramp to those values.

Symbology Stretch

  • Band selects the band to stretch when you have a multiband dataset.
  • Label refers to the labels in the Contents pane.
  • Display background value activates and sets the background. When checked on, the background displays as the selected color. Often this is set as transparent so you only see the data that has information.
  • Nodata sets the color for all pixels with NoData values.
  • Stretch type defines the range of values to display.
  • Gamma controls the amount of contrast in moderate pixel values.
  • Statistics determines how statistics are calculated. DRA counts all of the pixels currently on the screen to determine the statistics. As you move around the image, the statistics are recomputed automatically. Dataset uses the entire dataset to calculate statistics, regardless of where you have zoomed and panned around to. Custom allows you to input your own statistics. You have Options for importing statistics from another dataset, from an .xml file, and for saving custom statistics.

Stretch options

You can access these options from the Menu button at the top of the Symbology pane.

You have the option to import a layer file, a package, or a color map to set the parameters.

You can save your current symbology as a raster function template.

Under the Advanced tab, you can format the labels of category names. As you make changes here, they will be updated immediately in the Contents pane.

Colormap

When Colormap is selected, it applies the color map associated with the raster.

Symbology Colormap

Colormap options

You can access these options from the Menu button at the top of the Symbology pane.

You have the option to import a layer file, a package, or a color map to set the parameters.

You can save your current symbology as a raster function template.

Under the Advanced tab, you can format the labels of category names. As you make changes here, they will be updated immediately in the Contents pane.

Classify

Classify allows you to group pixels together in a specified number of classes. You can then edit the break points between each class.

Symbology Classify

  • Field represents the values of the data.
  • Normalization allows you to divide the values from Field by another attribute. You also have options for Percent of total and Log normalization techniques.
  • Method refers to how the break points are calculated.
  • Classes sets the number of groups.
  • Color scheme chooses the color ramp for displaying your data.
  • Nodata chooses the color for displaying NoData values.

Use the table to make changes to individual groups, such as changing the color of a particular group of values, or adjusting its range of values.

Classify options

You can access these options from the Menu button at the top of the Symbology pane.

You have the option to import a layer file, a package, or a color map to set the parameters.

You can save your current symbology as a raster function template.

Under the Advanced tab, you can format the labels of category names. As you make changes here, they will be updated immediately in the Contents pane. From here, you have the option to exclude values or set the sample size as well. Any values within the range set on Exclude Values will be displayed as NoData. To estimate the statistics and resulting histogram, you can use a skip factor, which will systematically sample pixels based on the number of rows and columns you want to skip. You can ignore values as well to adjust how the image is rendered by not including those values in the distribution.

Discrete

The Discrete symbology displays your dataset using a specific number of colors. Each color represents the same number of values.

Symbology Discrete

Discrete options

You can access these options from the Menu button at the top of the Symbology pane.

You have the option to import a layer file, a package, or a color map to set the parameters.

You can save your current symbology as a raster function template.

Vector Field

Vector Field uses a magnitude and direction component, or a U and V component, to display your data. A common use is to display ocean or wind currents as arrows where the direction indicates the flow and the size of the arrow is related to the power of the current.

Symbology Vector Field

By default, the pane is set up to work with data that shows magnitude and direction. You can also use the Vector Field renderer to visualize a single raster layer with a vector symbol. Select the appropriate bands or variables for these inputs. There are two ways to calculate flow. Meteorological displays the vectors based on the direction from which the current is coming. Oceanographic is the opposite; it shows the direction to which the current is flowing.

There are several options for Symbol type, including a single arrow, which is a generic option applicable to many scenarios. You also have options for displaying wind as barbs or based on the Beaufort wind scale and for displaying ocean currents.

Symbol spacing refers to the amount of area that each vector represents on the map.

Symbol size ranges from 0 to 100. Decreasing this range from its full extent allows you to visualize a greater level of detail in the moderate values.

The More properties button adjusts the minimum and maximum value for the magnitudes, changes the units, and adjusts the angle reference system and direction.

Vector Field renderer options

You can access these options from the Menu button at the top of the Symbology pane.

You have the option to import a layer file, a package, or a feature layer to set the parameters.

You can save your current symbology as a raster function template.

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