How to | Import and Export File Elements
Sometimes you may want to work with a specific part of a file instead of all of it. When bringing a file into the Wolfram Language, you can elect to import just individual parts of the file, which are called elements. The Wolfram Language's ability to import and export elements of files gives you greater control over the information being exchanged while simultaneously saving time and memory.
Use "Elements" as the second argument in Import to view the elements of the image that are available for import:
You can now analyze the image data, for example by using ListPlot3D:
The specific Import and Export elements that can be used depend on the file formats you are working with. For more information, see the documentation pages for the formats. There is also some additional information in How to: Import and Export.