CGContextDrawImage off Screen performance

Question

I have been using the following code to create an image off the screen (creating a
context, off-screen in background thread using GDC ) and later render it in the
main thread on the screen only when i receive updated "array of UIImages"
.
I found by doing so the rending path , lines .etc was much faster then dowing it the
drawRect: method of the UIView .

The issue that I'm facing now is that when trying to rending UIImage class using
CGContextDrawImage() it get really slow over ~1.4-2.5 sec to render. From searching
the main issue was that it spends most of its time deflating the png file. I have
tried infating the png image and use CGImageRef still long rending time. I dont have
a control on the data array that contain list if png files it comes in.
Would breaking the image to small pieces or and, using CALayer help , how i can stitch
those images without using "CGContextDrawImage" is it possible ?
I'm not sure what is best way to fix this issues and how , any Idea ?

Thanks In Advance

 void creatImageInBackground 
 {
     size = CGSizeMake (self.frame.size.width,self.frame.size.height);
     UIGraphicsBeginImageContextWithOptions(size, NO, 0.0); 
     CGContextRef context = UIGraphicsGetCurrentContext();
     CGContextSetInterpolationQuality(context, kCGInterpolationNone);
     UIGraphicsPushContext(context);
     for(UIImage * img in imgList )
     {
       ulXY = <calcuate >;
       lrXY = <calcuate >;
       imRec = CGRectMake( ulXY.x,-ulXY.y,(lrXY.x-ulXY.x) ,(lrXY.y -ulXY.y) );
       CGContextTranslateCTM( context, 0,(lrXY.y-ulXY.y) );
       CGContextScaleCTM(context, 1, -1);
       CGContextDrawImage(context, imRec,[[img image] CGImage]);
       //[img drawInRect:imRec];
      }

     UIGraphicsPopContext();
     [outputImage release];
     outputImage = UIGraphicsGetImageFromCurrentImageContext() ;
     [outputImage retain];
     UIGraphicsEndImageContext();

    dispatch_async(dispatch_get_main_queue(), ^(void)
    {
        [self setNeedsDisplay];
        [self setHidden:NO];
    });

}


    Then 
   - (void)drawRect:(CGRect)rect
   {
      CGPoint imagePoint = CGPointMake(0, 0);
      [outputImage drawAtPoint:imagePoint];
   }