Depth of Field...

That's deep!

So let's talk Depth of Field. What is Depth of Field? How does it work? Where is it used in games? As Depth of Field grows in prominence in the world of gaming, we begin to see how effective it is and how often it is used and in what capacity. Adapted from the science of photography, depth of field is a post-processing affect that is used to illustrate, emphasize and create dramatic effect in photography, movies, shows and games. Turn on the television and you're bound to see this technique used in some capacity. It is popular and agreeably one of the most notable and intuitive gifts from the world of photography. But as with all effects, there are those that disagree with its effectiveness in video games and believe that the gaming industry could do without it. 

This blog aims to explore the science of the effect, what's behind it all, how it's used and why people just can't get a long with it.

Depth of Field Explained

Depth of Field refers to the range of distance that appears acceptably sharp and varies based on three factors:

1. Aperture Size

2. Focal Length

3. Subject-to-camera distance

Everything immediately in front of or in the back of the focusing distance gradually loses sharpness and blurs out. This is relative due to the fact that a DOF can either be short or long. 

Aperture lens is the adjustable hole through which light passes. To understand aperture size, the term Circle of Confusion must be explained. When light rays bounce of a point on an object, they reflect the specific point on the object in several directions. This happens in the shape of a cone which travels to the camera lens. Once it reaches here the rays are bent by the lens to converge at a single point on the focusing plane. This is the part of the object that is "in focus". Based on where the various rays of light hit the focusing plane, a circle is formed relative to the distance of the object in relation to the image plane. This circle is known as the Circle of Confusion. 

There is a permissible circle of confusion which dictates the area of true focus on the focusing plane. Any circle of confusion larger than this permissible circle is automatically out of focus. Whereas any circle smaller than the permissible one is considered in focus. These are used to determine the depth of focus which is directly co-related to the depth of field. The aperture size is then related to how much light is being allowed in on the focusing plane. In short, increasing the aperture size decreases the depth of focus and therefore the depth of field while decreasing the aperture size increases the depth of focus and inherently the depth of field. 

At this point, let's talk about focal length. Focal length is a measurement of how strongly a lens focuses light. It's distance is measured from the center of an optical lens to the focusing plane while the lens is focused at infinity. The focal length effectively changes the subject's reproduced image size in the subject area covered by the lens. This is known as the Field of View. In summary, the smaller the focal length (wide focal lens), the longer the depth of field and the larger the focal length (narrower focal lens), the shorter the depth of field.

Finally, the subject-to camera distance from the camera's lens to in focus subject. Simply, the larger the distance between the subject and the camera, the larger the depth of field will be. Inversely, the smaller the distance between the subject and the camera, the shorter the depth of field will be. 

Notice the focus on aperture size and the detailed explanation of the circle of confusion and focusing plane. This is due to the fact that the best way to adjust the depth of field is by adjusting the aperture size. Now that the science is out of the way, let's move on to how Depth of Field is used in games.

Gaming Applications

Depth of field is used in many instances as a clever way of pointing the player to where they need to go. In cutscenes, it is used as a means of drawing the character's attention to important characters while less important ones are blurred in the back. A common technique is when depth of field is used to focus the player's attention on specific details and crucial areas in an environment or even to make clear the path to follow in order to achieve the objective. 

Games like Call of Duty and Far Cry effectively use depth of field to focus the player's view on their specified target when zooming in and aiming down their sights. This ensures that the player can hone in on the kill by blurring the unnecessary clutter around the field of focus and ensuring that the player's range of sight is limited to the area around the gun's barrel. 

Sometimes depth of field is used to drive players' focus away from certain areas in the game and keep them focused on their current path. This is true of games like Witcher 2 where depth of field is effective in discouraging unnecessary exploration.

In games like Second Life where beautiful landscapes are recognized, depth of field can be used to focus the player's attention on, let's just say the finer things the game has to offer. 

Another important application of depth of field can be seen in Assassin's Creed where most executions involve spying on the assassin's target from amidst crowds of citizens while waiting for the opportune moment to strike. In this situation, depth of field is used to blur out the throng of people and focus in on the templar target who must be assassinated. 

Besides these applications lie numerous ways to implement depth of field effectively in to game mechanics to enhance the player's experience. Most games utilize depth of field in simpler ways, such as blurring distant and hard to reach areas which discourage players from attempting to reach places not meant to be visited. Other games use depth of field to point players in the right direction or to highlight the path meant to be taken or the manner in which an objective is meant to be completed. Most gamers playthrough tons of these scenarios without realizing how well the developers have managed to incorporate amazing post processing effects into their solid core of gameplay. 

Issues on the table & Conclusion

A lot of gamers believe that depth of field is ugly and unnecessary in gaming. These are the same people who don't particularly appreciate the beauty of post processing and turn all effects off to enjoy the game in its true raw form. While I am not trying to criticize these people, it is sometimes important to note the trouble that goes into implementing these effects within video games and appreciate the developers for taking the time to make the game look cleaner, crisper and simply better.

Time and time again the fact that some companies do it right while other may not is brought to the table. Let's look at a clear example of how it can be used negatively. In Stalker: Clear Sky, depth of field is utilized whenever the player reloads their gun. When this happens, everything but the gun is blurred. This sucks for two very valid reasons, you want to know who you're going to be aiming for once your gun is cocked and ready for another barrage of bullets, and you need to know who's shooting you and where you're going to go/what you're going to do about it. Games where effects such as depth of field aren't seamlessly woven into gameplay give post-processing a bad name.

Besides this, the argument is made on several forums that our eyes naturally focus in on what we're looking at, inherently blurring everything around our point of focus. Some gamers believe that depth of field must only be used in non-interactive cutscenes while others argue that such effects hurt their eyes and cause headaches. I can sympathize with this but have seen either side of the fence and have to say that I would take a game that does depth of field right in a heartbeat rather than shutting the effect down altogether. 

In conclusion, depth of field is a positively wonderful post processing effect if used in moderation effectively and efficiently to enhance gameplay. It is often easy mistake the boundary and over-do it, in essence, creating a headache for gamers and potential fans. The true gems are the games that manage to integrate depth of field into their games in a versatile manner without bringing it to the player's attention. This can be done and done well as demonstrated by several companies out there.

At the end of the day, give game developers a chance to wow you. If they fail, well then you can say you told them so.