CODEWITHSUNDEEP
iosuiimagensattributedstringuigraphicscontext
Marco
Marco

Reputation: 6692

"Inverse" UIImage from NSAttributedString

I create a UIImage from an NSAttributedString:

UIFont *font = [UIFont systemFontOfSize:12.0f];
NSDictionary *attributes = @{NSFontAttributeName:font,
                             NSForegroundColorAttributeName:[UIColor greenColor]};

NSAttributedString *attributedString = [[NSAttributedString alloc] initWithString:title attributes:attributes];

// Create the image here
UIImage *image = [self imageFromAttributedString:attributedString];


#pragma mark - Get image from attributed string

- (UIImage *)imageFromAttributedString:(NSAttributedString *)text
{
    UIGraphicsBeginImageContextWithOptions(text.size, NO, 0.0);

    // draw in context
    [text drawAtPoint:CGPointMake(0.0, 0.0)];

    // transfer image
    UIImage *image = [UIGraphicsGetImageFromCurrentImageContext() imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
    UIGraphicsEndImageContext();

    return image;
}

My question is, what's the best way to create an image with the same text, but "reversed", i.e. [UIColor greenColor] with white font text?

Upvotes: 0

Views: 1205

Answers (2)

antont
antont

Reputation: 2756

Use NSBackgroundColorAttributeName to set background for green and NSForegroundColorAttributeName the text to white.

The docs include:

NSString *const NSForegroundColorAttributeName;
NSString *const NSBackgroundColorAttributeName;

at https://developer.apple.com/library/ios/documentation/UIKit/Reference/NSAttributedString_UIKit_Additions/Reference/Reference.html#//apple_ref/doc/uid/TP40011688

Upvotes: 1

Paulo
Paulo

Reputation: 1245

Once you have an image you can use Core Image Filters to reverse the colour or change blue to pink or red or whatever you wish: There is a CI Filter called CIColorInvert which will simply reverse the colours but personally I prefer using the colorMatrix filter which gives me more control code to reverse are the following:

Note this routine assumes your starting UIImage is beginImage the output is endImage

Using ColorMatrix:

 CIFilter *filterci = [CIFilter filterWithName:@"CIColorMatrix"  //rgreen
                                keysAndValues: kCIInputImageKey, beginImage, nil];
[filterci setValue:[CIVector vectorWithX:-1 Y:0 Z:0 W:0] forKey:@"inputRVector"]; // 5
[filterci setValue:[CIVector vectorWithX:0 Y:-1 Z:0 W:0] forKey:@"inputGVector"]; // 6
[filterci setValue:[CIVector vectorWithX:0 Y:0 Z:-1 W:0] forKey:@"inputBVector"]; // 7
[filterci setValue:[CIVector vectorWithX:0 Y:0 Z:0 W:1] forKey:@"inputAVector"]; // 8
[filterci setValue:[CIVector vectorWithX:0 Y:0 Z:0 W:0] forKey:@"inputBiasVector"];     
 CIImage *boutputImagei = [filterci outputImage];

  CGImageRef cgimgi = [context createCGImage:boutputImagei fromRect:[boutputImage extent]];
UIImage *endImage = [UIImage imageWithCGImage:cgimgi];

 CGImageRelease(cgimgi);

Using CIColorInvert:

CIFilter *filterci = [CIFilter filterWithName:@"CIColorInvert"  //rgreen
                                keysAndValues: kCIInputImageKey, beginImage, nil];
    CIImage *boutputImagei = [filterci outputImage];

  CGImageRef cgimgi = [context createCGImage:boutputImagei fromRect:[boutputImage extent]];
UIImage *endImage = [UIImage imageWithCGImage:cgimgi];

 CGImageRelease(cgimgi);

Upvotes: 0

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