# Using an Input Region

You can specify an input region to perform image-processing on a portion of the input image and choose from several region shapes. The output image will be the size of the pixel-aligned bounding box around the shape you choose. See the topic One Image Operator Edit Control for details. The Pixel Set operator supports two different region shape modes:

- Bounding Box: All pixels that lie within a pixel-aligned bounding box around the shape of the region are considered Care pixels and are set to the grey value defined by Pixel Value when you choose the operation SetCarePels.
- Masked Region: All pixels that lie within a pixel-aligned bounding box around the shape of the region, but are outside the region shape itself, are considered Don't Care pixels and are set to the grey value defined by Pixel Value when choose the operation SetDontCarePels. Pixels within the region shape are set to the grey value defined by Pixel Value when you choose the operation SetCarePels.

Note: The IPOneImage tool generally supports a third region mode option for affine rectangle transforms, but the Pixel Set operator does not support that mode.

Since choosing the Bounding Box region mode treats all pixels within the bounding box as Care pixels, the effect of the Pixel Set operator is to create an output image with all Care or all Don't Care pixels, similar to not using any region at all. Choosing the Masked Region mode, however, creates Care and Don't Care pixels depending on the shape of the region you choose: