图片压缩后长度和宽度 及像素坐标

CGFloatscaleFloat = 0.6;
+ (UIImage *) scaleImage: (UIImage *)p_w_picpath scaleFactor:(float)scaleFloat
{
CGSize size = CGSizeMake(p_w_picpath.size.width * scaleBy, p_w_picpath.size.height * scaleBy);

UIGraphicsBeginImageContext(size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGAffineTransform transform = CGAffineTransformIdentity;

transform = CGAffineTransformScale(transform, scaleBy, scaleBy);
CGContextConcatCTM(context, transform);

// Draw the p_w_picpath into the transformed context and return the p_w_picpath
[p_w_picpath drawAtPoint:CGPointMake(0.0f, 0.0f)];
UIImage *newimg = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

return newimg;
}

然后imgData = UIImageJPEGRepresentation(p_w_picpath, 0.6f)
imgDataUIImageJPEGRepresentation(p_w_picpath, scaleFloat)