Merging Layers of image in iPhone

CGImageRef _backgroundImageViewRef = _backgroundImageViewInTweek.image.CGImage;

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

CGContextRef contextRef = CGBitmapContextCreate(NULL, _backgroundImageViewInTweek.image.size.width, _backgroundImageViewInTweek.image.size.height,

8, _backgroundImageViewInTweek.image.size.width * 4,

colorSpace, kCGImageAlphaPremultipliedLast|kCGBitmapByteOrderDefault);

CGContextDrawImage(contextRef, CGRectMake(0, 0, _backgroundImageViewInTweek.image.size.width, _backgroundImageViewInTweek.image.size.height), _backgroundImageViewRef);

CGContextSetLineWidth(contextRef, 4);

CGContextSetRGBStrokeColor(contextRef, 0.0, 0.0, 1.0, 0.5);

CGRect costume_rect = CGContextConvertRectToDeviceSpace(contextRef, CGRectMake(0.0f,0.0f,171, 217));

CGContextDrawImage(contextRef, costume_rect, _costumeImageViewInTweek.image.CGImage); 

UIImage *_mergingBackgroundAndCostumeImage;

_mergingBackgroundAndCostumeImage =[UIImage imageWithCGImage:CGBitmapContextCreateImage(contextRef)];

CGContextRelease(contextRef);

CGColorSpaceRelease(colorSpace);

With Regards,

Dinesh Sharma

color code detection in VB

 Public Function ConvertToGrayscale(ByVal source As Bitmap) as Bitmap

  Dim bm as new Bitmap(source.Width,source.Height)

  Dim x

  Dim y

  For y=0 To bm.Height

    For x=0 To bm.Width

      Dim c as Color = source.GetPixel(x,y)

      Dim luma as Integer = CInt(c.R*0.3 + c.G*0.59 + c.B*0.11)

      bm.SetPixel(x,y,Color.FromArgb(luma,luma,luma)

    Next

  Next

  Return bm

End Function

How to Mask an Image

- (UIImage*) maskImage:(UIImage *)image withMask:(UIImage *)maskImage {

CGImageRef maskRef = maskImage.CGImage; 

CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),

CGImageGetHeight(maskRef),

CGImageGetBitsPerComponent(maskRef),

CGImageGetBitsPerPixel(maskRef),

CGImageGetBytesPerRow(maskRef),

CGImageGetDataProvider(maskRef), NULL, false);

CGImageRef masked = CGImageCreateWithMask([image CGImage], mask);

return [UIImage imageWithCGImage:masked];

}

Crop an image using the iPhone SDK

One of the pieces of Game Trivia Catechism that I've been putting off for some time is the timer displayed on the question screen.  The timer is basically a reverse progress indicator.  It starts out full (with all of the lights on) and slowly counts down to empty (all lights off).  The simplest method I know of for building a progress indicator is to use two images (one full, one empty) and simply crop the "full" to an appropriate sized based on the current progress position.

When it came time to implement this in GTC, I scoured the Cocoa Touch documentation for an easy way to crop a UIImage down to a specific size.  Apparently this was something that didn't make the cut.  Fortunately the lower level CoreGraphics methods provide a fairly simple method of doing this.  Here's what I ended up with.

- (UIImage*)imageByCropping:(UIImage *)imageToCrop toRect:(CGRect)rect
{
   //create a context to do our clipping in
   UIGraphicsBeginImageContext(rect.size);
   CGContextRef currentContext = UIGraphicsGetCurrentContext();

   //create a rect with the size we want to crop the image to
   //the X and Y here are zero so we start at the beginning of our
   //newly created context
   CGRect clippedRect = CGRectMake(0, 0, rect.size.width, rect.size.height);
   CGContextClipToRect( currentContext, clippedRect);

   //create a rect equivalent to the full size of the image
   //offset the rect by the X and Y we want to start the crop
   //from in order to cut off anything before them
   CGRect drawRect = CGRectMake(rect.origin.x * -1,
                                rect.origin.y * -1,
                                imageToCrop.size.width,
                                imageToCrop.size.height);

   //draw the image to our clipped context using our offset rect
   CGContextDrawImage(currentContext, drawRect, imageToCrop.CGImage);

   //pull the image from our cropped context
   UIImage *cropped = UIGraphicsGetImageFromCurrentImageContext();

   //pop the context to get back to the default
   UIGraphicsEndImageContext();

   //Note: this is autoreleased
   return cropped;
}

Then call the code with something like:
- (void)drawRect:(CGRect)rect
{
   //draw the whole lights off image
   //the on images will be drawn overtop
   [lightsOffImage drawInRect:rect];

   //if we don't have any lights on... no point in continuing
   if( numberOfLightsOn < 1 )
     return;

   //figure out the dimensions of numberOfLights on bulbs
   CGSize croppedSize = CGSizeMake(LIGHT_WIDTH * numberOfLightsOn, LIGHT_HEIGHT);
   CGRect clippedRect = CGRectMake(0, 0, croppedSize.width, croppedSize.height);

   //get the "on" bulbs by cropping the image
   UIImage *cropped = [self imageByCropping:lightsOnImage toRect:clippedRect];

   //create a rect to draw the newly cropped on images to
   CGRect lightsOnRect = CGRectMake(LIGHT_BULB_OFFSET_X,
                                    LIGHT_BULB_OFFSET_Y,
                                    croppedSize.width,
                                    croppedSize.height);

   //draw the "on" lights
   [cropped drawInRect:lightsOnRect];

   //cropped is autoreleased so no need to worry about cleanup
}

Regards,
dinesh