之前对于图片的概念很模糊，一直以为直接拿来用就ok啦，最近项目中发现原来没那么简单，需要处理一下，比如各种类型的图片大小就不一样，像素也不尽相同，所有一般拿到图片对他进行处理之后使用，往往可以节省不少资源，这对于开发手机应用来说帮助不少；
把图片先转换成位图在使用：
+ (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.
else if (!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),
0,
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 = [UIImage imageWithCGImage:decompressedImageRef scale:image.scale orientation:image.imageOrientation];
CGImageRelease(decompressedImageRef);
return decompressedImage;
}
把图片转换成特地大小的位图在使用：
+ (UIImage *)decodedImageWithImage:(UIImage *)image withSize:(CGSize)transSize
{
if (image.images)
{
// Do not decode animated images
return image;
}
CGImageRef imageRef = image.CGImage;
CGSize imageSize = transSize;//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.
else if (!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),
0,
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 = [UIImage imageWithCGImage:decompressedImageRef scale:image.scale orientation:image.imageOrientation];
CGImageRelease(decompressedImageRef);
return decompressedImage;
}