根据图片格式定义，实现快速读取图的分辨率大小,支持 jpg、png、gif、bmp四种格式图片格式。此类未做全面测试，当遇到不能处理的图片，会用.Net自带的Iamage类进行读取。-According to the image format definition, achieve rapid read figure size, the resolution of support JPG, PNG, GIF, BMP format picture format.Such did not fully test, when cannot handle picture, will use. Net own Iamage class to read.