// 根据图片url获取图片尺寸

+(CGSize)getImageSizeWithURL:(id)imageURL

{

    NSURL* URL = nil;

    if([imageURL isKindOfClass:[NSURL
class]]){

        URL = imageURL;

    }

    if([imageURL isKindOfClass:[NSString
class]]){

        URL = [NSURL
URLWithString:imageURL];

    }

    if(URL == nil)

        return
CGSizeZero;                  // url不正确返回CGSizeZero

     

    NSMutableURLRequest
*request = [[NSMutableURLRequest
alloc] initWithURL:URL];

    NSString* pathExtendsion = [URL.pathExtension lowercaseString];

     

    CGSize size = CGSizeZero;

    if([pathExtendsion isEqualToString:@"png"]){

        size =  [self
getPNGImageSizeWithRequest:request];

    }

    else
if([pathExtendsion isEqual:@"gif"])

    {

        size =  [self
getGIFImageSizeWithRequest:request];

    }

    else{

        size = [self
getJPGImageSizeWithRequest:request];

    }

    if(CGSizeEqualToSize(CGSizeZero, size))                    // 如果获取文件头信息失败,发送异步请求请求原图

    {

        NSData* data = [NSURLConnection
sendSynchronousRequest:[NSURLRequest
requestWithURL:URL] returningResponse:nil
error:nil];

        UIImage* image = [UIImage
imageWithData:data];

        if(image)

        {

            size = image.size;

        }

    }

    return
size;

}

//  获取PNG图片的大小

+(CGSize)getPNGImageSizeWithRequest:(NSMutableURLRequest*)request

{

    [request setValue:@"bytes=16-23"
forHTTPHeaderField:@"Range"];

    NSData* data = [NSURLConnection
sendSynchronousRequest:request returningResponse:nil
error:nil];

    if(data.length == 8)

    {

        int
w1 = 0, w2 = 0, w3 = 0, w4 = 0;

        [data getBytes:&w1 range:NSMakeRange(0, 1)];

        [data getBytes:&w2 range:NSMakeRange(1, 1)];

        [data getBytes:&w3 range:NSMakeRange(2, 1)];

        [data getBytes:&w4 range:NSMakeRange(3, 1)];

        int
w = (w1 << 24) + (w2 << 16) + (w3 << 8) + w4;

        int
h1 = 0, h2 = 0, h3 = 0, h4 = 0;

        [data getBytes:&h1 range:NSMakeRange(4, 1)];

        [data getBytes:&h2 range:NSMakeRange(5, 1)];

        [data getBytes:&h3 range:NSMakeRange(6, 1)];

        [data getBytes:&h4 range:NSMakeRange(7, 1)];

        int
h = (h1 << 24) + (h2 << 16) + (h3 << 8) + h4;

        return
CGSizeMake(w, h);

    }

    return
CGSizeZero;

}

//  获取gif图片的大小

+(CGSize)getGIFImageSizeWithRequest:(NSMutableURLRequest*)request

{

    [request setValue:@"bytes=6-9"
forHTTPHeaderField:@"Range"];

    NSData* data = [NSURLConnection
sendSynchronousRequest:request returningResponse:nil
error:nil];

    if(data.length == 4)

    {

        short
w1 = 0, w2 = 0;

        [data getBytes:&w1 range:NSMakeRange(0, 1)];

        [data getBytes:&w2 range:NSMakeRange(1, 1)];

        short
w = w1 + (w2 << 8);

        short
h1 = 0, h2 = 0;

        [data getBytes:&h1 range:NSMakeRange(2, 1)];

        [data getBytes:&h2 range:NSMakeRange(3, 1)];

        short
h = h1 + (h2 << 8);

        return
CGSizeMake(w, h);

    }

    return
CGSizeZero;

}

//  获取jpg图片的大小

+(CGSize)getJPGImageSizeWithRequest:(NSMutableURLRequest*)request

{

    [request setValue:@"bytes=0-209"
forHTTPHeaderField:@"Range"];

    NSData* data = [NSURLConnection
sendSynchronousRequest:request returningResponse:nil
error:nil];

     

    if
([data length] <= 0x58) {

        return
CGSizeZero;

    }

     

    if
([data length] < 210) {// 肯定只有一个DQT字段

        short
w1 = 0, w2 = 0;

        [data getBytes:&w1 range:NSMakeRange(0x60, 0x1)];

        [data getBytes:&w2 range:NSMakeRange(0x61, 0x1)];

        short
w = (w1 << 8) + w2;

        short
h1 = 0, h2 = 0;

        [data getBytes:&h1 range:NSMakeRange(0x5e, 0x1)];

        [data getBytes:&h2 range:NSMakeRange(0x5f, 0x1)];

        short
h = (h1 << 8) + h2;

        return
CGSizeMake(w, h);

    } else
{

        short
word = 0x0;

        [data getBytes:&word range:NSMakeRange(0x15, 0x1)];

        if
(word == 0xdb) {

            [data getBytes:&word range:NSMakeRange(0x5a, 0x1)];

            if
(word == 0xdb) {// 两个DQT字段

                short
w1 = 0, w2 = 0;

                [data getBytes:&w1 range:NSMakeRange(0xa5, 0x1)];

                [data getBytes:&w2 range:NSMakeRange(0xa6, 0x1)];

                short
w = (w1 << 8) + w2;

                short
h1 = 0, h2 = 0;

                [data getBytes:&h1 range:NSMakeRange(0xa3, 0x1)];

                [data getBytes:&h2 range:NSMakeRange(0xa4, 0x1)];

                short
h = (h1 << 8) + h2;

                return
CGSizeMake(w, h);

            } else
{// 一个DQT字段

                short
w1 = 0, w2 = 0;

                [data getBytes:&w1 range:NSMakeRange(0x60, 0x1)];

                [data getBytes:&w2 range:NSMakeRange(0x61, 0x1)];

                short
w = (w1 << 8) + w2;

                short
h1 = 0, h2 = 0;

                [data getBytes:&h1 range:NSMakeRange(0x5e, 0x1)];

                [data getBytes:&h2 range:NSMakeRange(0x5f, 0x1)];

                short
h = (h1 << 8) + h2;

                return
CGSizeMake(w, h);

            }

        } else
{

            return
CGSizeZero;

        }

    }

}

摘自: https://blog.csdn.net/chenyong05314/article/details/52585492