Raster rendering behavior
ArcGIS will display your raster data with the most appropriate renderer according to the raster properties (such as number of bands, source type, pixel type, and statistics) and metadata that is available. You can control the default rendering using the application's Options dialog box by changing the settings on the Raster > Raster Layer tabs.
You can interactively choose different rendering methods based on your display and analysis needs once the raster data is added to the display. You can change these methods using the Image Analysis window or by opening the layer's Properties dialog box and editing the parameters on the Symbology tab. To preserve the rendering properties you've set, you can save a layer (*.lyr) file.
For all raster datasets and mosaic datasets, there is a Source Type property, such as elevation or thematic, that describes the data. This property affects how the data is rendered. For example, for elevation the default resampling method is bilinear and the default stretch is Min-Max and for thematic nearest neighbor resampling is used with a standard deviation stretch. If the value is Processed, then no stretch will be applied.
Rendering raster products
Raster products are designed to make adding imagery from specific sensors or data providers to your map simpler because each raster product has a unique set of enhancements and band combinations to provide an optimal view of your data. The stretch, band combinations, and necessary functions are added to enhance the layer to modify the display. However, like any other layer you can modify these functions once they are added to the map.
Each raster product has a default template. This will typically be Multispectral. Therefore, if you don't expand the raster product to choose a different template, then this default will be used.
Rendering single-band datasets
When a single-band raster dataset is drawn, the rules for determining the default renderer are as follows:
- If your dataset has a color map, it will be displayed with the Colormap renderer using the colors stored in the color map.
- If your dataset contains 1-bit data and the dataset does not have pyramids, the Unique Values renderer will be used with 0 set to white and 1 set to black. When 1-bit data has pyramids, the Stretched renderer will be used. Pyramid files for 1-bit data are created as 8-bit grayscale to achieve improved display when viewing the raster at its full extent.
- If your dataset contains 25 or fewer unique values, the Unique Values renderer will be used with random colors assigned to the values.
- If your dataset has an internally stored custom stretch, the Stretched renderer will be used with a color ramp from black to white.
- If your dataset has statistics, the Stretched renderer will be used with a color ramp from black to white, using the most appropriate stretch type for the data. If there are no statistics stored with your dataset, they will be sampled from the dataset and the Stretched renderer will be applied; however, these statistics will only be used for the display and will not be stored with the dataset.
Rendering multiband datasets
When a multiband raster dataset is drawn the default uses the RGB Composite renderer. If the data has wavelength information, then it will be displayed with the red, green, and blue bands, otherwise it will use the default band combination on the Raster tab of the Options dialog box. If your dataset does not have statistics, they will be sampled from the dataset and the RGB Composite renderer will be applied; however, these statistics will only be used for the display and will not be stored with the dataset.
Rendering mosaic datasets
A mosaic dataset is a data model within the geodatabase used to manage a collection of raster datasets (images) stored as a catalog and viewed as a mosaicked image. When you add a mosaic dataset to ArcMap, it is added as a mosaic layer that appears in the table of contents as a special group layer with a minimum of three layers: Boundary, Footprint, and Image. When you add a mosaic dataset to ArcGlobe, it appears as a single layer—a raster layer.
The Image layer is used to control the rendering of the mosaicked image of the mosaic dataset. You can right-click the Image layer to open the Properties dialog box, and like the raster dataset, you can change the renderer on the Symbology tab. Modifications you make to the Image layer properties do not affect the mosaic dataset—just how it is rendered at the time you are viewing it.
Rendering alpha bands
An alpha band acts as a transparency mask, providing a transparency value for each pixel. An alpha band can be toggled on or off for multiple-band raster datasets rendered with the RGB Composite renderer.
If you want to toggle the Alpha channel on or off, you will need to check the appropriate check box to turn it on or uncheck it to turn it off within the Symbology tab of the raster layer Properties dialog box.
Rendering raster catalogs
A raster catalog is a collection of raster datasets defined in table format in which the records specify the individual rasters in the catalog. Raster catalogs can also be used to hold disparate, semioverlapping, or fully overlapping raster datasets.
The raster datasets in the raster catalog are displayed in order, from the first to last record in the catalog's table. By default, if more than nine images are in the current display extent, raster catalogs are displayed as a wireframe; otherwise, the actual raster data will be displayed. Using the wireframe speeds up the display of raster catalogs. The default of nine images can be changed in the display properties of your raster catalog or on the Raster tab on the Options dialog box.
ArcMap can render each raster dataset member of a geodatabase raster catalog with its most appropriate renderer. The Symbology tab of a raster catalog's Layer Properties dialog box lists the renderers available for the catalog. This list can be edited by adding or removing various renderers. Only the renderers in the list can be used to render the catalog. In the available renderers list, ArcMap places an asterisk next to each of the currently active renderers that are applied to one or more raster dataset members of the raster catalog. However, the active list can only be triggered when an image is displayed on-screen. This list will not be complete until the entire catalog has been viewed. The active renderers persist even after you change the display to another area, to the full extent, or back to a wireframe display.
As mentioned, each raster catalog item is rendered with an appropriate renderer in the list, following similar rules as a raster dataset. Therefore, the classified renderer will never be a default renderer, unless it is the only renderer in the available renderer list.