Remove alpha channel from UIImage

Question

I use the following method to get the unpacked uiimage from the file system. However, the UIImageView is red when I turn on the color mixed layer, even if the UIImageView is set to Opaque.

Images in the file system do not have an alpha channel. I tried setting CGContextSetAlpha (bitmapContext, 1) but still has a mixed layer.

Does anyone know how to remove an 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;
}

Answer 1

In the context settings, try the option

kCGImageAlphaNoneSkipLast

or

kCGImageAlphaNoneSkipFirst

Depending on whether you use RGBA or ARGB

t

CGContextRef bitmapContext = CGBitmapContextCreate(NULL,
                                                       rect.size.width,
                                                       rect.size.height,
                                                       CGImageGetBitsPerComponent(imageRef),
                                                       CGImageGetBytesPerRow(imageRef),
                                                       CGImageGetColorSpace(imageRef),
                                                       kCGImageAlphaNoneSkipLast | kCGBitmapByteOrder32Little
                                                       );

Answer 2

-(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"];