Add solid color border with CIImage

Question

I'm looking for a way to add a solid color border to an existent image with Core Image. I've found the filter list reference but there is no one to make it.

Help !!

Answer 1

We need to have the CIImage extent or the CGRect in which we want to create the solid border. Than, We can draw a CIImage forming a solid line in the specified area, and repeat the steps for 3 more times for different positions to draw a complete solid rectangle. Following is the piece of code which will draw a straight solid line above the specified area.

CIImage *overlay1 = [CIImage imageWithColor:[CIColor colorWithRed:255/255.f green:0/255.f blue:0/255.f alpha:1.00f]];
    overlay1 = [overlay1 imageByCroppingToRect:image.extent];
    overlay1 = [overlay1 imageByApplyingFilter:@"CIPerspectiveTransformWithExtent" withInputParameters:@{@"inputExtent":[CIVector vectorWithCGRect:image.extent],@"inputTopLeft":[CIVector vectorWithCGPoint:CGPointMake(topLeft.x - 5, topLeft.y + 5)],@"inputTopRight":[CIVector vectorWithCGPoint:CGPointMake(topRight.x + 5, topRight.y + 5)],@"inputBottomLeft":[CIVector vectorWithCGPoint:CGPointMake(topLeft.x - 5, topLeft.y )],@"inputBottomRight":[CIVector vectorWithCGPoint:CGPointMake(topRight.x + 5, topRight.y ) ]}];
    overlay = [ overlay1 imageByCompositingOverImage:overlay];

I have kept the width for 5 pixels. topLeft , topRight.... are the respective CGPoint for the position. For a complete rectangle you will also need bottomLeft and bottomRight.

Overlay is the original CIImage .

Answer 2

This isn't exactly what you asked about, but it might be better if you just want to display the image with a border (rather than actually drawing a border onto it)...

You can use CALayer to add borders (and rounded corners, shadows, etc.) to any UIView...

// imgView is an instance of UIImageView, but this works with any UIView
imgView.layer.borderWidth = 2.0f;
imgView.layer.borderColor = [[UIColor blackColor] CGColor];

You also need to #import <QuartzCore/QuartzCore.h> and link to the QuartzCore framework for this to work.