Why tiny memory leak in this func related to UIGraphicsBeginImageContext?-Collection of common programming errors

I have a simple function to create an UIImage with special size :

- (UIImage*)imageWithSize:(CGSize) imSize
{
    UIGraphicsBeginImageContext( imSize );

    float r = 0.5f;
    float g = 0.5f;
    float b = 0.5f;

    CGContextRef cxt = UIGraphicsGetCurrentContext();
    CGContextSetRGBStrokeColor(cxt, r, g, b, 1.0);
    CGContextSetRGBFillColor(cxt, r,g,b, 1.0);
    CGContextFillRect(cxt, CGRectMake(0.0, 0.0, imSize.width, imSize.height));

    UIImage* retImg = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return retImg;
}

and then I call it MANY times in this way (I’m using ARC):

for(int i=0;i