1. An image processing apparatus which develops RAW image data obtained by an image sensing apparatus having an imaging sensor, comprising: a magnification setting device that sets, in accordance with a user's operation, a magnification representing a ratio of a number of pixels within a display region of a display device to a number of pixels in a corresponding area in the RAW image data; a read out device that reads out RAW image data; a developing device that develops RAW image data; an extracting device that extracts, from the RAW image data, a number of pixels less than a number of all of pixels included in the RAW image data in accordance with the magnification set by said magnification setting device, where the lesser the magnification setting device sets the magnification, the lesser ratio at which said extracting device extracts pixels if the magnification is less than 100%; a control device that causes said developing device to develop the pixels extracted by said extracting device; and a display control device that controls the display device to display, within the display region, the image data developed by said developing device.