The CRParallaxMotionEffect class allows setting up parallax more easily in iOS 7.

CRParallaxMotionEffect.h

//
//  CRParallaxMotionEffect.h
//  CeedBase
//
//  Created by Raphael Sebbe on 23/07/13.
//  BSD License (3-clause). Copyright (c) 2013 Creaceed. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface CRParallaxMotionEffect : UIMotionEffect
@property (readonly) CGFloat horizontalAmplitude, verticalAmplitude;

// For "center" property
// Positive -> closer to viewer (foreground)
// Negative -> farther to viewer (background)

// Remark: the opposite for contentOffset in scrollview.

// default keypath is "center"
+ (instancetype)parallaxEffectWithAmplitude:(CGFloat)ampli;
+ (instancetype)parallaxEffectWithHorizontalAmplitude:(CGFloat)xampli verticalAmplitude:(CGFloat)yampli;
+ (instancetype)parallaxEffectWithAmplitude:(CGFloat)ampli pointKeyPath:(NSString*)pkeypath;
+ (instancetype)parallaxEffectWithHorizontalAmplitude:(CGFloat)xampli verticalAmplitude:(CGFloat)yampli pointKeyPath:(NSString*)pkeypath;

@end

CRParallaxMotionEffect.m

//
//  CRParallaxMotionEffect.m
//  CeedBase
//
//  Created by Raphael Sebbe on 23/07/13.
//  BSD License (3-clause). Copyright (c) 2013 Creaceed. All rights reserved.
//

#import "CRParallaxMotionEffect.h"
#import "UIDevice+CeedBase.h"

@interface CRParallaxMotionEffect ()
@property (readwrite) CGFloat horizontalAmplitude, verticalAmplitude;
@property (readwrite) NSString *pointKeyPath;
@end

@implementation CRParallaxMotionEffect
+ (instancetype)parallaxEffectWithAmplitude:(CGFloat)ampli
{
	return [self parallaxEffectWithHorizontalAmplitude:ampli verticalAmplitude:ampli pointKeyPath:@"center"];
}
+ (instancetype)parallaxEffectWithAmplitude:(CGFloat)ampli pointKeyPath:(NSString*)pkeypath
{
	return [self parallaxEffectWithHorizontalAmplitude:ampli verticalAmplitude:ampli pointKeyPath:pkeypath];
}
+ (instancetype)parallaxEffectWithHorizontalAmplitude:(CGFloat)xampli verticalAmplitude:(CGFloat)yampli
{
	return [self parallaxEffectWithHorizontalAmplitude:xampli verticalAmplitude:yampli pointKeyPath:@"center"];
}
+ (instancetype)parallaxEffectWithHorizontalAmplitude:(CGFloat)xampli verticalAmplitude:(CGFloat)yampli pointKeyPath:(NSString*)pkeypath;
{
	CRParallaxMotionEffect *res = [[[self alloc] init] autorelease];
	
	res.horizontalAmplitude = xampli;
	res.verticalAmplitude = yampli;
	res.pointKeyPath = pkeypath;
	
	return res;
}

- (void)dealloc
{
	self.pointKeyPath = nil;
}

- (NSDictionary *)keyPathsAndRelativeValuesForViewerOffset:(UIOffset)viewerOffset
{
	CGFloat deviceScaling = 1.0;// could reduce it for iPhone, for instance.
	
	return @{ self.pointKeyPath: [NSValue valueWithCGPoint:
		  CGPointMake(viewerOffset.horizontal*self.horizontalAmplitude * deviceScaling,
		  viewerOffset.vertical*self.verticalAmplitude * deviceScaling  )]
	};
}

@end