UIImageの画像の拡大・縮小・反転・回転

UIImageの画像をリサイズ、回転、反転したい場合がある。こんなときにはQuartz 2D APIを使用する。Quartz 2D APIはCore Graphicsフレームワークの一部。

CTM(Current Transformation Matrix）を使う。主に以下の3つ。

CGContextTranslateCTM : 原点の平行移動 CGContextRotateCTM : 原点を中心として座標系を回転 CGContextScaleCTM : 原点を中心として座標系を拡大縮小

①とりあえずそのまま描画

- (UIImage*)drawImage

{

    UIImage *original_img = [UIImage imageNamed:@"frog"];


    UIGraphicsBeginImageContext(self.view.bounds.size);

    [original_img drawInRect:CGRectMake(0, 0, original_img.size.width, original_img.size.height)];

    UIImage *final_img = UIGraphicsGetImageFromCurrentImageContext();


    UIGraphicsEndImageContext();


    return final_img;

}

 

②画像を平行移動させて描画する場合 CGContextTranslateCTMで座標系を平行移動

- (UIImage*)drawImageWithTranslateCTM

{

    UIImage *original_img = [UIImage imageNamed:@"frog"];


    UIGraphicsBeginImageContext(self.view.bounds.size);

    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextTranslateCTM(context, 100, 100);


    [original_img drawInRect:CGRectMake(0, 0, original_img.size.width, original_img.size.height)];

    UIImage *final_img = UIGraphicsGetImageFromCurrentImageContext();


    UIGraphicsEndImageContext();


    return final_img;

}

 

③画像を回転させて描画する場合 CGContextRotateCTMで座標系を回転

- (UIImage*)drawImageWithRotateCTM

{

    UIImage *original_img = [UIImage imageNamed:@"frog"];


    UIGraphicsBeginImageContext(self.view.bounds.size);

    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextRotateCTM(context, 30 * M_PI/180);


    [original_img drawInRect:CGRectMake(0, 0, original_img.size.width, original_img.size.height)];

    UIImage *final_img = UIGraphicsGetImageFromCurrentImageContext();


    UIGraphicsEndImageContext();


    return final_img;

}

 

④画像を縮小して描画する場合 CGContextScaleCTMで座標系を縮小

- (UIImage*)drawImageWithScaleCTM

{

    UIImage *original_img = [UIImage imageNamed:@"frog"];


    UIGraphicsBeginImageContext(self.view.bounds.size);

    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextScaleCTM(context, 0.5, 0.5);


    [original_img drawInRect:CGRectMake(0, 0, original_img.size.width, original_img.size.height)];

    UIImage *final_img = UIGraphicsGetImageFromCurrentImageContext();


    UIGraphicsEndImageContext();


    return final_img;

}

 

④画像を反転して描画する場合 CGContextScaleCTMで座標系をマイナス方向に拡大してCGContextTranslateCTMで平行移動

- (UIImage*)drawImageInverted{

    UIImage *original_img = [UIImage imageNamed:@"frog"];


    UIGraphicsBeginImageContext(self.view.bounds.size);

    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextScaleCTM(context, -1, 1.0);

    CGContextTranslateCTM(context, -self.view.bounds.size.width, 0);


    [original_img drawInRect:CGRectMake(0, 0, original_img.size.width, original_img.size.height)];

    UIImage *final_img = UIGraphicsGetImageFromCurrentImageContext();


    UIGraphicsEndImageContext();


    return final_img;

}