Image services

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An image service provides access to raster data through a Web service. The source of the raster data can be a raster dataset (from a geodatabase or file on disk), a layer file referencing a raster dataset, or a compiled image service definition (containing one or more raster datasets and defined processes) created using ArcGIS Image Server. Once you publish this raster data to your server, you can use the resulting image service in ArcGIS Desktop the same way you would add any other GIS service layer.

Important: If you plan on creating image services based on compiled image service definitions, you must register ArcGIS Image Server with ArcGIS Server.

Learn more about registering ArcGIS Image Server with ArcGIS Server.

Image service capabilities

When you publish an image service, you can choose to enable it with Open Geospatial Consortium Web Map Service (WMS) or Web Coverage Service (WCS) capabilities. The raster data source that you use to publish your service determines the capabilities and layer properties that are available to you. A default capability of imaging is always enabled.

Preparing image services

There are many things to consider when you are preparing to create an image service, because not all raster data will be served in an equal manner depending on the capabilities you choose.

How many raster datasets are there?

If you have a single raster dataset that you want to serve, such as a mosaicked raster dataset in ArcSDE or a large digital elevation model (DEM), then ArcGIS Server can serve this directly. If, however, you need to serve many raster datasets that will compose a single image service, or you want to serve up many raster datasets that overlap completely and were captured at various dates or times that will compose a single image service, you should use the ArcGIS Image Server extension. Use the Image Service Definition Editor toolbar in ArcMap (provided with the extension) to create a compiled image service definition. You can then publish this to your server.

Can a raster catalog be served as an image service?

A raster catalog cannot be served as an image service; however, if the raster catalog is unmanaged, you can easily point to the folder or folders containing the source data and create an image service definition that can be served as an image service.

Is the raster data available for viewing as an image or as input for analysis?

The raster data is available for both viewing as an image and as input for analysis, depending on which capabilities you enable when you publish the service. If the users of the image service will not be making adjustments to the appearance of the image, other than adjusting things like transparency, brightness, and contrast, and will not be using the raster data as input for any analysis, then this data can be served with any of the capabilities. If the user will be accessing the data in the image service to do further analysis, such as spatial analysis with the geoprocessing tools or generating a surface from elevation data, then you should enable the WCS capability for the image service.

Does the data have multiple bands or need to be enhanced?

The layer properties of a non-WMS image service allow you to change the band combination or apply a stretch to the histogram to enhance the appearance of the image. If serving a raster dataset using WMS you cannot change the rendering or the band combination, therefore, only a raster dataset layer and image service definition are valid inputs for a WMS service. If an image service definition is used, the output properties need to be defined as 3-band color (RGB) or 1-band grayscale.

Is any processing required?

When you serve a raster dataset or layer file referencing a raster dataset, it must be in its final state and ready for the user to use. However, when you publish a compiled image service definition, the server performs on-the-fly processing such as orthorectification, enhancements, band combinations, band algebra, pan sharpening, and filtering.

Publishing image services

Your options for publishing image services will vary depending on which software you have:

Using (consuming) an image service

You can access an image service the same way you would any other service by first connecting to the GIS Server, then choosing the image service that is available.

Learn about adding an image service layer to ArcMap

Layer properties for raster dataset sources

The image service layer has properties, similarly to any other layer in ArcGIS. Like a raster dataset layer, the Image Service Layer Properties dialog box contains the General, Source, Extent, Display, and Symbology tabs. The General, Source, Extent, and Display tabs are similar to the raster dataset layer and other layers; however, the Display tab has an additional option to control the compression of the transmitted image service. This transmission compression can be preset in an image service definition; however, the user will always have the ability to change this. A highly compressed image will be transmitted faster than an uncompressed image, but the image quality may not be as good. The Symbology tab is similar to the raster dataset layer; however, the user will only have the option to change the renderer using the RGB or Stretched renderers. Here the user can change the renderer, change the stretch applied to the histogram, and alter the background color and NoData representation.

Additional layer properties for the ArcGIS Image Server source

When the image service is created from an image service definition, additional layer properties are presented on two additional tabs--the Mosaic tab and the Metadata tab. The Mosaic tab allows the user to change the mosaic method, such as By Attribute or Closest to Center; choose a field that will contain values used to sort on when using the By Attribute mosaic method; and specify the value by which the imagery will be ordered. The Metadata tab provides information about the image service, the returned image, any processes that were applied, and specifics about the source datasets. This information will be available for any image service that is derived from an image service definition, whether it is served from ArcGIS Server or the ArcGIS Image Server stand-alone configuration.

Further reading

For a detailed example of preparing, publishing, and using an image service, see Tutorial: Publishing an image service.