问题
I use the following method to get a decompressed uiimage from file system. However the UIImageView is colored as red when I turn on the color blended layer, even though the UIImageView is set to Opaque.
The images on file system don't have alpha channel. I tried set CGContextSetAlpha(bitmapContext, 1), but still has blended layer.
Anyone know how to remove alpha channel when using CGContextDrawImage?
- (UIImage *)decompressedImage
{
CGImageRef imageRef = self.CGImage;
CGRect rect = CGRectMake(0.f, 0.f, CGImageGetWidth(imageRef), CGImageGetHeight(imageRef));
CGContextRef bitmapContext = CGBitmapContextCreate(NULL,
rect.size.width,
rect.size.height,
CGImageGetBitsPerComponent(imageRef),
CGImageGetBytesPerRow(imageRef),
CGImageGetColorSpace(imageRef),
kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little
);
// kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little are the bit flags required
// so that the main thread doesn't have any conversions to do.
CGContextDrawImage(bitmapContext, rect, imageRef);
CGImageRef decompressedImageRef = CGBitmapContextCreateImage(bitmapContext);
UIImage* decompressedImage = [UIImage imageWithCGImage:decompressedImageRef
scale:[[UIScreen mainScreen] scale]
orientation:UIImageOrientationUp];
CGImageRelease(decompressedImageRef);
CGContextRelease(bitmapContext);
return decompressedImage;
}
回答1:
In the options for the context, try the option
kCGImageAlphaNoneSkipLast
or
kCGImageAlphaNoneSkipFirst
Depending on if you are using RGBA or ARGB
ie,
CGContextRef bitmapContext = CGBitmapContextCreate(NULL,
rect.size.width,
rect.size.height,
CGImageGetBitsPerComponent(imageRef),
CGImageGetBytesPerRow(imageRef),
CGImageGetColorSpace(imageRef),
kCGImageAlphaNoneSkipLast | kCGBitmapByteOrder32Little
);
回答2:
Same result but less code and things to worry about:
func removeAlpha(from inputImage: UIImage) -> UIImage {
let format = UIGraphicsImageRendererFormat.init()
format.opaque = true //Removes Alpha Channel
format.scale = inputImage.scale //Keeps original image scale.
let size = inputImage.size
return UIGraphicsImageRenderer(size: size, format: format).image { _ in
inputImage.draw(in: CGRect(origin: .zero, size: size))
}
}
回答3:
-(void)JhagRemoveMethodRepet
{
switch (Jhagtag)
{
case 1:
{
if (jhag1.alpha>0.3)
{
float alpha1;
alpha1=jhag1.alpha;
jhag1.alpha=alpha1-0.1;
[Checkjhag replaceObjectAtIndex:0 withObject:@"Mid"];
}else
{
jhag1.alpha=0.0;
[JRemovetimer invalidate];
JRemovetimer=nil;
[Checkjhag replaceObjectAtIndex:0 withObject:@"No"];
[self checkcompeletewater];
}
}
break;
case 2:
{
if (jhag2.alpha>0.3)
{
float alpha1;
alpha1=jhag2.alpha;
jhag2.alpha=alpha1-0.1;
[Checkjhag replaceObjectAtIndex:1 withObject:@"Mid"];
if (jhagBrush==YES)
{
BTooth2.alpha=0.0;
}
}else
{
jhag2.alpha=0.0;
[JRemovetimer invalidate];
JRemovetimer=nil;
[Checkjhag replaceObjectAtIndex:1 withObject:@"No"];
[self checkcompeletewater];
}
}
break;
case 3:
{
if (jhag3.alpha>0.3)
{
float alpha1;
alpha1=jhag3.alpha;
jhag3.alpha=alpha1-0.1;
[Checkjhag replaceObjectAtIndex:2 withObject:@"Mid"];
}else
{
jhag3.alpha=0.0;
[JRemovetimer invalidate];
JRemovetimer=nil;
[Checkjhag replaceObjectAtIndex:2 withObject:@"No"];
[self checkcompeletewater];
}
}
break;
case 4:
{
if (jhag4.alpha>0.3)
{
float alpha1;
alpha1=jhag4.alpha;
jhag4.alpha=alpha1-0.1;
[Checkjhag replaceObjectAtIndex:3 withObject:@"Mid"];
if (jhagBrush==YES)
{
BTooth3.alpha=0.0;
SpiderMud.alpha=0.0;
}
}else
{
jhag4.alpha=0.0;
[JRemovetimer invalidate];
JRemovetimer=nil;
[Checkjhag replaceObjectAtIndex:3 withObject:@"No"];
[self checkcompeletewater];
}
}
break;
case 5:
{
if (jhag5.alpha>0.3)
{
float alpha1;
alpha1=jhag5.alpha;
jhag5.alpha=alpha1-0.1;
[Checkjhag replaceObjectAtIndex:4 withObject:@"Mid"];
}else
{
jhag5.alpha=0.0;
[JRemovetimer invalidate];
JRemovetimer=nil;
[Checkjhag replaceObjectAtIndex:4 withObject:@"No"];
[self checkcompeletewater];
}
}
break;
case 6:
{
if (jhag6.alpha>0.3)
{
float alpha1;
alpha1=jhag6.alpha;
jhag6.alpha=alpha1-0.1;
[Checkjhag replaceObjectAtIndex:5 withObject:@"Mid"];
if (jhagBrush==YES)
{
GreenMud.alpha=0.0;
}
}else
{
jhag6.alpha=0.0;
[JRemovetimer invalidate];
JRemovetimer=nil;
[Checkjhag replaceObjectAtIndex:5 withObject:@"No"];
[self checkcompeletewater];
}
}
break;
case 7:
{
if (jhag7.alpha>0.3)
{
float alpha1;
alpha1=jhag7.alpha;
jhag7.alpha=alpha1-0.1;
[Checkjhag replaceObjectAtIndex:6 withObject:@"Mid"];
}else
{
jhag7.alpha=0.0;
[JRemovetimer invalidate];
JRemovetimer=nil;
[Checkjhag replaceObjectAtIndex:6 withObject:@"No"];
[self checkcompeletewater];
}
}
break;
case 8:
{
if (jhag8.alpha>0.3)
{
float alpha1;
alpha1=jhag8.alpha;
jhag8.alpha=alpha1-0.1;
[Checkjhag replaceObjectAtIndex:7 withObject:@"Mid"];
if (jhagBrush==YES)
{
BTooth1.alpha=0.0;
}
}else
{
jhag8.alpha=0.0;
[JRemovetimer invalidate];
JRemovetimer=nil;
[Checkjhag replaceObjectAtIndex:7 withObject:@"No"];
[self checkcompeletewater];
}
}
break;
case 9:
{
if (jhag9.alpha>0.3)
{
float alpha1;
alpha1=jhag9.alpha;
jhag9.alpha=alpha1-0.1;
[Checkjhag replaceObjectAtIndex:8 withObject:@"Mid"];
}
else
{
jhag9.alpha=0.0;
[JRemovetimer invalidate];
JRemovetimer=nil;
[Checkjhag replaceObjectAtIndex:8 withObject:@"No"];
[self checkcompeletewater];
}
}
break;
case 10:
{
if (jhag10.alpha>0.3)
{
float alpha1;
alpha1=jhag10.alpha;
jhag10.alpha=alpha1-0.1;
[Checkjhag replaceObjectAtIndex:9 withObject:@"Mid"];
}else
{
jhag10.alpha=0.0;
[JRemovetimer invalidate];
JRemovetimer=nil;
[Checkjhag replaceObjectAtIndex:9 withObject:@"No"];
[self checkcompeletewater];
}
}
break;
case 11:
{
if (jhag11.alpha>0.3)
{
float alpha1;
alpha1=jhag11.alpha;
jhag11.alpha=alpha1-0.1;
[Checkjhag replaceObjectAtIndex:10 withObject:@"Mid"];
if (jhagBrush==YES)
{
Yellowmud.alpha=0.0;
}
}else
{
jhag11.alpha=0.0;
[JRemovetimer invalidate];
JRemovetimer=nil;
[Checkjhag replaceObjectAtIndex:10 withObject:@"No"];
[self checkcompeletewater];
}
}
break;
default:
break;
}
}
-(void)checkcompeletewater
{
NSMutableArray *compeletearr=[NSMutableArray arrayWithObjects:@"No",@"No",@"No",@"No",@"No",@"No",@"No",@"No",@"No",@"No",@"No", nil];
if ([Checkjhag isEqualToArray:compeletearr] && jhagBrush==YES)
{
waterClean=YES;
[self SoundPlay:@"puzzle_right"];
来源：https://stackoverflow.com/questions/21416358/remove-alpha-channel-from-uiimage