5.7　Scanning of Aerial Photographs

5.7.1　The resolution of photographs shall not be less than 25μm.

5.7.2　The scanned images shall be correctly exposed and have appropriate hue，gray level，gradation，contrast，and bar graphs.The optical images shall be clear and complete.The scanned images shall have their gray level values normally distributed in the range of 0-255.

5.7.3　The scanned fiducial marks shall be clear and complete.

5.7.4　The image files shall be in the format of TIF.