图片解码方法

编程基础 • 2025-01-07 17:17 • 阅读 44

采用SDWebImage中的实现方法：

+ (UIImage *)decodedImageWithImage:(UIImage *)image {

if (image.images) {

// Do not decode animated images

return image;

}

CGImageRef imageRef = image.CGImage;

CGSize imageSize =CGSizeMake(CGImageGetWidth(imageRef),CGImageGetHeight(imageRef));

CGRect imageRect = (CGRect){.origin =CGPointZero, .size = imageSize};

CGColorSpaceRef colorSpace =CGColorSpaceCreateDeviceRGB();

CGBitmapInfo bitmapInfo =CGImageGetBitmapInfo(imageRef);

int infoMask = (bitmapInfo &kCGBitmapAlphaInfoMask);

BOOL anyNonAlpha = (infoMask ==kCGImageAlphaNone ||

infoMask == kCGImageAlphaNoneSkipFirst ||

infoMask == kCGImageAlphaNoneSkipLast);

// CGBitmapContextCreate doesn't support kCGImageAlphaNone with RGB.

// https://developer.apple.com/library/mac/#qa/qa1037/_index.html

if (infoMask ==kCGImageAlphaNone && CGColorSpaceGetNumberOfComponents(colorSpace) >1) {

// Unset the old alpha info.

bitmapInfo &= ~kCGBitmapAlphaInfoMask;

// Set noneSkipFirst.

bitmapInfo |= kCGImageAlphaNoneSkipFirst;

}

// Some PNGs tell us they have alpha but only 3 components. Odd.

elseif (!anyNonAlpha && CGColorSpaceGetNumberOfComponents(colorSpace) ==3) {

// Unset the old alpha info.

bitmapInfo &= ~kCGBitmapAlphaInfoMask;

bitmapInfo |= kCGImageAlphaPremultipliedFirst;

}

// It calculates the bytes-per-row based on the bitsPerComponent and width arguments.

CGContextRef context =CGBitmapContextCreate(NULL,

imageSize.width,

imageSize.height,

CGImageGetBitsPerComponent(imageRef),

colorSpace,

bitmapInfo);

CGColorSpaceRelease(colorSpace);

// If failed, return undecompressed image

if (!context)return image;

CGContextDrawImage(context, imageRect, imageRef);

CGImageRef decompressedImageRef =CGBitmapContextCreateImage(context);

CGContextRelease(context);

UIImage *decompressedImage = [UIImageimageWithCGImage:decompressedImageRefscale:image.scaleorientation:image.imageOrientation];

CGImageRelease(decompressedImageRef);

return decompressedImage;

}

简单说就是：

根据当前输入image的CGImageRef；

根据CGImageRef得到CGSize；

根据CGImageRef生成CGBitmapInfo；

生成一个颜色空间；

根据以上值，生成一个CGBitmap画布，然后draw 一个CGRect大小的CGImageRef;

根据以上画布，得到一个新的CGImageRef;

根据以上CGImageRef生成一个UIImage，返回；

今天的文章图片解码方法分享到此就结束了，感谢您的阅读。

图片解码方法

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