文章轉自:iOS 圖片壓縮限制大小最優解

這里的maxLength 入參 可以這樣寫
比如指定 壓縮成400kb
400.f * 1024.f 即可

/** 壓縮圖片方法(先壓縮質量再壓縮尺寸)*/ -(NSData *)compressWithLengthLimit:(NSUInteger)maxLength; /** 壓縮圖片方法(壓縮質量)*/ -(NSData *)compressQualityWithLengthLimit:(NSInteger)maxLength; /** 壓縮圖片方法(壓縮質量二分法)*/ -(NSData *)compressMidQualityWithLengthLimit:(NSInteger)maxLength; /** 壓縮圖片方法(壓縮尺寸)*/ -(NSData *)compressBySizeWithLengthLimit:(NSUInteger)maxLength; -(NSData *)compressWithLengthLimit:(NSUInteger)maxLength{// Compress by qualityCGFloat compression = 1;NSData *data = UIImageJPEGRepresentation(self, compression);//NSLog(@"Before compressing quality, image size = %ld KB",data.length/1024);if (data.length < maxLength) return data;CGFloat max = 1;CGFloat min = 0;for (int i = 0; i < 6; ++i) {compression = (max + min) / 2;data = UIImageJPEGRepresentation(self, compression);//NSLog(@"Compression = %.1f", compression);//NSLog(@"In compressing quality loop, image size = %ld KB", data.length / 1024);if (data.length < maxLength * 0.9) {min = compression;} else if (data.length > maxLength) {max = compression;} else {break;}}//NSLog(@"After compressing quality, image size = %ld KB", data.length / 1024);if (data.length < maxLength) return data;UIImage *resultImage = [UIImage imageWithData:data];// Compress by sizeNSUInteger lastDataLength = 0;while (data.length > maxLength && data.length != lastDataLength) {lastDataLength = data.length;CGFloat ratio = (CGFloat)maxLength / data.length;//NSLog(@"Ratio = %.1f", ratio);CGSize size = CGSizeMake((NSUInteger)(resultImage.size.width * sqrtf(ratio)),(NSUInteger)(resultImage.size.height * sqrtf(ratio))); // Use NSUInteger to prevent white blankUIGraphicsBeginImageContext(size);[resultImage drawInRect:CGRectMake(0, 0, size.width, size.height)];resultImage = UIGraphicsGetImageFromCurrentImageContext();UIGraphicsEndImageContext();data = UIImageJPEGRepresentation(resultImage, compression);NSLog(@"In compressing size loop, image size = %ld KB", data.length / 1024);}NSLog(@"After compressing size loop, image size = %ld KB", data.length / 1024);return data; }- (NSData *)compressQualityWithLengthLimit:(NSInteger)maxLength {CGFloat compression = 1;NSData *data = UIImageJPEGRepresentation(self, compression);while (data.length > maxLength && compression > 0) {compression -= 0.02;data = UIImageJPEGRepresentation(self, compression); // When compression less than a value, this code dose not work}return data; }-(NSData *)compressMidQualityWithLengthLimit:(NSInteger)maxLength{CGFloat compression = 1;NSData *data = UIImageJPEGRepresentation(self, compression);if (data.length < maxLength) return data;CGFloat max = 1;CGFloat min = 0;for (int i = 0; i < 6; ++i) {compression = (max + min) / 2;data = UIImageJPEGRepresentation(self, compression);if (data.length < maxLength * 0.9) {min = compression;} else if (data.length > maxLength) {max = compression;} else {break;}}return data; }-(NSData *)compressBySizeWithLengthLimit:(NSUInteger)maxLength{UIImage *resultImage = self;NSData *data = UIImageJPEGRepresentation(resultImage, 1);NSUInteger lastDataLength = 0;while (data.length > maxLength && data.length != lastDataLength) {lastDataLength = data.length;CGFloat ratio = (CGFloat)maxLength / data.length;CGSize size = CGSizeMake((NSUInteger)(resultImage.size.width * sqrtf(ratio)),(NSUInteger)(resultImage.size.height * sqrtf(ratio))); // Use NSUInteger to prevent white blankUIGraphicsBeginImageContext(size);// Use image to draw (drawInRect:), image is larger but more compression time// Use result image to draw, image is smaller but less compression time[resultImage drawInRect:CGRectMake(0, 0, size.width, size.height)];resultImage = UIGraphicsGetImageFromCurrentImageContext();UIGraphicsEndImageContext();data = UIImageJPEGRepresentation(resultImage, 1);}return data; }

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