[英]How to know if a UIImage is representable in PNG or JPG?
我從UIImagePickerController
獲得了一個UIImage
,並使用了該站點中的代碼來調整圖像的大小
- (UIImage *)resizedImage:(CGSize)newSize
transform:(CGAffineTransform)transform
drawTransposed:(BOOL)transpose
interpolationQuality:(CGInterpolationQuality)quality {
CGRect newRect = CGRectIntegral(CGRectMake(0, 0, newSize.width, newSize.height));
CGRect transposedRect = CGRectMake(0, 0, newRect.size.height, newRect.size.width);
CGImageRef imageRef = self.CGImage;
// Build a context that's the same dimensions as the new size
CGContextRef bitmap = CGBitmapContextCreate(NULL,
newRect.size.width,
newRect.size.height,
CGImageGetBitsPerComponent(imageRef),
0,
CGImageGetColorSpace(imageRef),
CGImageGetBitmapInfo(imageRef));
// Rotate and/or flip the image if required by its orientation
CGContextConcatCTM(bitmap, transform);
// Set the quality level to use when rescaling
CGContextSetInterpolationQuality(bitmap, quality);
// Draw into the context; this scales the image
CGContextDrawImage(bitmap, transpose ? transposedRect : newRect, imageRef);
// Get the resized image from the context and a UIImage
CGImageRef newImageRef = CGBitmapContextCreateImage(bitmap);
UIImage *newImage = [UIImage imageWithCGImage:newImageRef];
// Clean up
CGContextRelease(bitmap);
CGImageRelease(newImageRef);
return newImage;
}
UIImagePNGRepresentation()
未能在調整大小的圖像上返回NSData
,但UIImageJPEGRepresentation()
成功。
我們如何知道UIImage
是否可以PNG或JPEG呈現? 上面的代碼中遺漏了哪些內容,無法使調整大小后的圖像無法用PNG表示?
根據Apple的文檔:“如果圖像沒有數據或基礎CGImageRef包含不受支持的位圖格式的數據,則此函數可能返回nil。”
PNG演示文稿支持哪種位圖格式? 如何制作UIImage PNG支持的格式?
這是一個錯誤,在代碼的另一部分中,圖像使用以下內容重新縮放
CGContextRef context = CGBitmapContextCreate(NULL,
size.width,
size.height,
8,
0,
CGImageGetColorSpace(source),
kCGImageAlphaNoneSkipFirst);
將kCGImageAlphaNoneSkipFirst更改為CGImageGetBitmapInfo(source)可解決此問題
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