Restrirct Boundary 320 x 480, while scaling UIImage

I am working on Interior Decoration Application, we can add Sofa, Table, Chair Table Lamp on Camera screen then can scale UIImage with touch to zoom picture. But by zooming we don't want to increase UIImage Size greater then 320 x 480, I mean want to restrict in iphone Boundary.

any suggestion, I had implemented and tried, but couldn't get exact solution. I use to check on base of center but this approach is not working, want some thing like Edge detection may be that would be exact solution,

Already Thanks, looking forwards

here is some code that I am using to Resize my UIImageView

-(BOOL)isValidSizeForView:(UIView *)myView forSize:(CGSize)size
{
    BOOL Decision = NO;

    CGRect rect = myView.frame;

    CGRect BoundRect = CGRectMake(0, 0, 320, 480);

    float MinX = (BoundRect.origin.x+(myView.frame.size.width/2));

    float MaxX = ((BoundRect.origin.x+BoundRect.size.width)-(myView.frame.size.width/2));

    float MinY = (BoundRect.origin.y+(myView.frame.size.height/2开发者_开发百科));

    float MaxY = ((BoundRect.origin.y+BoundRect.size.height)-(myView.frame.size.height/2));

    if(rect.origin.x > MinX && rect.origin.x< MaxX && rect.origin.y> MinY && rect.origin.y<MaxY)
    {
        Decision = YES;
    }
    else
    {
        printf(":( no sorry \n");
    }

    return Decision;
}

You could get the maximum zoomed size for your image by doing something like this:

- (CGSize)zoomedSizeForImage:(UIImage *)image constrainedTo:(CGSize)maxSize {
    CGFloat width = image.size.width;
    CGFloat height = image.size.height;
    if (width > maxSize.width) {
        width = maxSize.width;
        height = height * maxSize.width / width;
    }
    if (height > maxSize.height) {
        width = width * maxSize.height / height;
        height = maxSize.height;
    }
    return CGSizeMake(width, height);
}