Understanding the Image layer

The Image layer is a component of the mosaic dataset layer when it's added to ArcMap. It is used to control the rendering of the dynamically mosaicked image of the mosaic dataset. Modifications you make to the Image layer properties do not affect the mosaic dataset but only how it is rendered at the time you are viewing it. The Image layer is just like a raster layer—you can change the display properties, such as changing the renderer, band combination, or enhancement, as well as some specific properties, such as modifying the mosaic methods and viewing the properties of the dynamically mosaicked image.

Mosaic dataset layer

The Image layer is not optimized for speed, but it is dynamic, and any changes made to the mosaic dataset are reflected in the Image layer. When you are using a mosaic dataset, any processing required to generate the mosaicked image is done on the local desktop. Whereas if the mosaic dataset is served and you are connecting to the image service, the processing to generate the mosaicked image is done on the server.

When there are problems with the mosaic dataset, such as the boundary not having been generated or the functions defined in the function chain not generating a valid output, the Image layer may not be checked, and it will appear with a small red Exclamation.

Right-clicking the Image layer in ArcMap displays the shortcut menu with the following options:

Image layer properties

To access the Layer Properties dialog box of the Image layer, right-click the Image layer and click Properties.

The Image layer properties of the mosaic dataset are somewhat unique and are very similar to the layer properties of the image service serving the mosaic dataset. Through the Display tab, you can change the transmission compression. A highly compressed image is transmitted faster than an uncompressed image; however, the image quality may not be as good.

Transmission compression

The Mosaic tab is unique to the mosaic dataset (or an image service created from a mosaic dataset). Since the mosaicked image can be created from a number of input rasters, there are two settings to assist you in viewing the mosaicked image you need. The mosaic method defines how the mosaic is created from different rasters, such as By Attribute, where a field containing values is used to sort the images, or Closest to Center, where the image closest to the center of the display is on top.

The mosaic methods include

The mosaic operator allows you to define how to resolve the overlapping cells, such as choosing a blending operation.

The mosaic operators include

Both First and Last minimize the amount of data that is read; therefore, they will be the fastest methods. Min, Max, Mean, and Blend require the overlapping cells to be read, so these methods can be slower.

The Status tab presents the image properties of the mosaicked image, including the extent, number of rows and columns, number of bands, pixel depth, and compression information.

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