Viewport parameters are applied to the region specified by the Presentation State and/or Source Image Region, if present; otherwise, the Viewport Query Parameters are applied to the full original image.

If both rows and columns Query Parameters are specified, then each shall be interpreted as a maximum, and a size will be chosen for the returned image within these constraints, maintaining the aspect ratio of the selected region.

If the rows Query Parameter is absent and the columns Query Parameter is present, the number of rows in the returned image shall be chosen to maintain the aspect ratio of the selected region.

If the columns Query Parameter is absent and the rows Query Parameter is present, the number of columns in the returned image shall be chosen to maintain the aspect ratio of the selected region.

If both Query Parameters are absent, the image (or selected region) is returned with its original size (or the size of the presentation state applied to the image), resulting in one pixel in the returned image for each pixel in the original image.