If you double the image resolution (for example, from 75 dpi to 150 dpi) without changing other settings, render time can increase by 2 to 4 times. (Depending on the complexity of the image being rendered, the increase in render time can vary from 1.9 to 3.9 times, with an average of 2.7 times the render time of the original 75-dpi image.)

If you double the resolution again (from the original 75 dpi to 150 dpi, then to 300 dpi), each jump in resolution increases render time by 2.7 times. Therefore, if you increase the resolution from 75 dpi to 300 dpi, the render time is typically increased 2.7 x 2.7 times, or about 7.3 times the original 75-dpi render time. If you increase the resolution from 75 dpi to 600 dpi, the render time is typically increased 2.7 x 2.7 x 2.7 times, or about 19.7 times the original 75-dpi render time.

When defining the view area to render, check that the image size is appropriate and reasonable. If you specify a very large image size, the render speed may be very slow.

• Crop region: When using a crop region to define the view area to render, you can specify the height and width of the crop region. (See Resizing Crop Regions Explicitly.) The crop region size defines the paper size of the rendered image.
• Render region: When using a render region to define the view area to render in an orthographic view, you can drag the render region boundary. ( Defining the View Area to Render.) The resulting height and width display in the Rendering dialog under Output.

See Controlling the Size of the Rendered Image.