最近阅读了一些大佬关于图片优化的博客，但是没有具体的demo，所以根据大佬提的优化方案，写了一个demo。
参考地址：https://www.jianshu.com/p/7d8a82115060?utm_campaign=maleskine&utm_content=note&utm_medium=seo_notes&utm_source=recommendation
本demo使用了降采样和异步处理进行优化
1、降采样：
//UIKit方式
-(UIImage*)resizeUI:(CGSize)size{
UIGraphicsBeginImageContextWithOptions(size, YES, 0);
[self drawInRect:CGRectMake(0, 0, size.width, size.height)];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
//CoreGraphics
-(UIImage*)resizeCG:(CGSize)size{
CGImageRef cgImage = self.CGImage;
if (cgImage == nil){
return nil;
}
size_t bitsPerComponent = CGImageGetBitsPerComponent(cgImage);
size_t bytesPerRow = CGImageGetBytesPerRow(cgImage);
CGColorSpaceRef colorSpace = CGImageGetColorSpace(cgImage);
CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(cgImage);
CGContextRef context = CGBitmapContextCreate(nil, size.width, size.height, bitsPerComponent, bytesPerRow, colorSpace, bitmapInfo);
CGContextSetInterpolationQuality(context, kCGInterpolationHigh);
CGContextDrawImage(context, CGRectMake(0, 0, size.width, size.height), cgImage);
CGImageRef bitmapImageRef = CGBitmapContextCreateImage(context);
UIImage *image = [UIImage imageWithCGImage:bitmapImageRef scale:self.scale orientation:self.imageOrientation];
return image;
}
//ImageIO
- (UIImage*)resizeIO:(CGSize)size{
NSData *data = UIImagePNGRepresentation(self);
if (data == nil){
return nil;
}
CGImageSourceRef imageSource = CGImageSourceCreateWithData((CFDataRef)data, nil);
if (imageSource == nil) {
return nil;
}
CFDictionaryRef property = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, nil);
NSDictionary *propertys = CFBridgingRelease(property);
CGFloat height = [propertys[@"PixelHeight"] integerValue]; //图像k宽高，12000
CGFloat width = [propertys[@"PixelWidth"] integerValue];
//以较大的边为基准
int imageSize = (int)MAX(size.width, size.height);
CFStringRef keys[5];
CFTypeRef values[5];
//创建缩略图等比缩放大小，会根据长宽值比较大的作为imageSize进行缩放
//kCGImageSourceThumbnailMaxPixelSize为生成缩略图的大小。当设置为800，如果图片本身大于800*600，则生成后图片大小为800*600，如果源图片为700*500，则生成图片为800*500
keys[0] = kCGImageSourceThumbnailMaxPixelSize;
CFNumberRef thumbnailSize = CFNumberCreate(NULL, kCFNumberIntType, &imageSize);
values[0] = (CFTypeRef)thumbnailSize;
keys[1] = kCGImageSourceCreateThumbnailFromImageAlways;
values[1] = (CFTypeRef)kCFBooleanTrue;
keys[2] = kCGImageSourceCreateThumbnailWithTransform;
values[2] = (CFTypeRef)kCFBooleanTrue;
keys[3] = kCGImageSourceCreateThumbnailFromImageIfAbsent;
values[3] = (CFTypeRef)kCFBooleanTrue;
keys[4] = kCGImageSourceShouldCacheImmediately;
values[4] = (CFTypeRef)kCFBooleanTrue;
CFDictionaryRef options = CFDictionaryCreate(kCFAllocatorDefault, (const void **)keys, (const void **)values, 4, &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks);
CGImageRef thumbnailImage = CGImageSourceCreateThumbnailAtIndex(imageSource, 0, options);
UIImage *resultImg = [UIImage imageWithCGImage:thumbnailImage];
return resultImg;
}
//CoreImage
- (UIImage*)resizeCI:(CGSize)size{
CGImageRef cgImage = self.CGImage;
if (cgImage == nil){
return nil;
}
CIImage *ciImageInput = [CIImage imageWithCGImage:cgImage];
double scale = size.width/self.size.height;
CIFilter *filter = [CIFilter filterWithName:@"CILanczosScaleTransform"];
[filter setValue:ciImageInput forKey:kCIInputImageKey];
[filter setValue:[NSNumber numberWithDouble:scale] forKey:kCIInputScaleKey];
[filter setValue:@(1.0) forKey:kCIInputAspectRatioKey];
CIImage *ciImageOutput = [filter valueForKey:kCIOutputImageKey];
if (!ciImageOutput) {
return nil;
}
CIContext *ciContext = [[CIContext alloc] initWithOptions:@{kCIContextUseSoftwareRenderer : @(NO)}];
CGImageRef ciImageRef = [ciContext createCGImage:ciImageOutput fromRect:CGRectMake(0, 0, size.width, size.height)];
UIImage *resultImg = [UIImage imageWithCGImage:ciImageRef];
return resultImg;
}
//vImage
- (UIImage*)resizeVI:(CGSize)size{
CGImageRef cgImage = self.CGImage;
if (cgImage == nil){
return nil;
}
vImage_CGImageFormat format;
format.bitsPerComponent = 8;
format.bitsPerPixel = 32; //ARGB四通道 4*8
format.colorSpace = nil; //默认sRGB
format.bitmapInfo = kCGImageAlphaFirst | kCGBitmapByteOrderDefault; // 表示ARGB
format.version = 0;
format.decode = nil; //默认色彩映射范围【0, 1.0】
format.renderingIntent = kCGRenderingIntentDefault;//超出【0，1】范围后怎么处理
//源图片buffer，输出图片buffer
vImage_Buffer sourceBuffer, outputBuffer;
vImage_Error error = vImageBuffer_InitWithCGImage(&sourceBuffer, &format, nil, cgImage, kvImageNoFlags);
if (error != kvImageNoError) {
return nil;
}
float scale = self.scale;
int width = (int)size.width;
int height = (int)size.height;
int bytesPerPixel = (int)CGImageGetBitsPerPixel(cgImage)/8;
//设置输出格式
outputBuffer.width = width;
outputBuffer.height = height;
outputBuffer.rowBytes = bytesPerPixel * width;
outputBuffer.data = malloc(outputBuffer.rowBytes * outputBuffer.height);
//缩放到当前尺寸上
error = vImageScale_ARGB8888(&sourceBuffer, &outputBuffer, nil, kvImageHighQualityResampling);
if (error != kvImageNoError) {
return nil;
}
CGImageRef outputImageRef = vImageCreateCGImageFromBuffer(&outputBuffer, &format, nil, nil, kvImageNoFlags, &error);
UIImage *resultImg = [UIImage imageWithCGImage:outputImageRef];
return resultImg;
}
2、异步加载：
-(void)update:(NSIndexPath *)indexPath{
NSURL *currentURL = [NSURL URLWithString:[self.imgURLArray objectAtIndex:indexPath.row]];
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
__weak typeof(self) weakSelf = self;
//异步下载图片
dispatch_async(queue, ^{
UIImage *images = [UIImage imageWithData:[NSData dataWithContentsOfURL:currentURL]];
CGSize size = CGSizeMake(images.size.width/10, images.size.height/10);
[images resizeCG:size];
weakSelf.imgs[currentURL] = images;
//更新UI
dispatch_async(dispatch_get_main_queue(), ^{
MyCollectionViewCell *cell = (MyCollectionViewCell *)[weakSelf.myCollectionView cellForItemAtIndexPath:indexPath];
cell.image = images;
});
});
self.tasks[currentURL] = queue;
}
demo地址：https://github.com/chenmengdi/load_image.git
filename (1).gif
