Investigative Study

Although it undoubtedly has certain characteristics of a photographic image, we would scarcely agree that this image is photoreal because it lacks features that are present in our physical world. For example, the glass sphere’s refraction appears too clean, and the shadow is too crisp and unrealistic. In short, the lighting situation seems artificial since there are no refractions, caustics, or indirect reflections and light bounces. In addition to these features, we also see a lack of depth-of-field, which we may attribute to the comparatively limited calculation of physical parameters of light propagation in early computer graphics. The outcome is an excessively clean and unnaturally sharp image. (Flueckiger, 2015)

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In addition to the characteristics mentioned above that are associated with creating photorealistic computer-generated images, artists use software to simulate the operation and effect of lighting and cameras further in the compositing stage of the VFX pipeline to create photorealism. CGI and digital composites can be enhanced with a variety of analogue artefacts, including noise and grain, depth-of-field, motion blur, lens flares, vignetting, and more. In addition, they can help develop artistic coherence in compositing through the seamless and convincing integration of visual elements from various sources.

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Camera Lens Artefacts
Since the virtual camera in CGI lacks physical lens configuration and analogue film features to produce a photoreal appearance for the renders, various optical effects can be added individually during the digital compositing process. (Mitchell, 1994) One of them is the depth-of-field, and there are others, such as grain, lens distortion, chromatic aberration, lens flare, vignetting, etc.

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In the 1990s, computer scientists created algorithms to enhance computer-generated images that appeared sterile and unnatural. (Flueckiger, 2015) They started to develop physical characteristics that could have come from the camera or the photochemical film, such as motion blur, depth of field, film grain, scratches, and dirt. These analogue artefact simulations go beyond simple enhancements of the original images by connecting them to the long-standing traditions of photography and film.

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The analogue photograph, not the digital one, frequently sets the standard for photorealism. (Gaut, 2010) For instance, because of the silver halides used, classic film has a characteristic called film grain, but digital photos have not. Other features used are common to both traditional and digital photography. For example, motion blur arises when an object has moved noticeably during the exposure time of the photo, and lens flare occurs when some light from a light source bounces off the lens rather than going through it.

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Grain, Scratches and Dust
Film grain is the random visual texture that can be seen in both photography and film. Tiny ‘grains’ in a photograph result from analogue still and moving image capture methods. They used to be little particles of silver halide - the photosensitive material needed for the chemical film that would randomly appear across photographs. However, as the medium developed and advanced, they were finally reduced.

As cinematographer Janusz Kaminski asserts, “If you can’t see or sense grain in the image, you’re not experiencing the magic of movies,” grains can be considered the core of the cinematic experience. (Flueckiger, 2015, p. 81)

As Barbara Flueckiger (2015) suggests, too much grain is now a sign of historicity in movies, either to indicate an older time period in the narrative or a character’s memory in a flashback. This type of grain effect is best used in conjunction with black-and-white or sepia-toned cinematography. 

Scratches and dust can be linked to film stock’s materiality or perceived as signs of extensive usage and old age of film. For instance, the Curious Case of Benjamin Button (2008) opens with a scene about a clockmaker who designs a clock that ticks backwards after losing his son in the war. (Flueckiger, 2015) The scene was enhanced by scratches, dirt, diffusion, and a colour palette that appeared historical.

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Depth-of-field (DOF)
Depth-of-field is inextricably linked to aperture, focus distance, focal length and circle of confusion. Wide-open aperture, large diameter, and telephoto lenses typically result in shallow depth of field.

However, depth-of-field (DOF) rendering in CGI was not even achievable until the late 1990s since it requires a systematic link between focus and depth in addition to the blurring of certain parts of the image. Furthermore, as the various pieces are first filmed or rendered in focus, DOF is a crucial issue not just in CGI but also in compositing, where the compositors must carefully create a link between the various image planes and their renderings of focus. (Flueckiger, 2015)

Ron Brinkmann (2008) demonstrates a significant distinction between a basic Gaussian blur—i.e., the computational averaging of neighbouring pixels using a Gaussian distribution—and the photographic quality of out-of-focus regions, known as bokeh, in his classic book The Art and Science of Digital Compositing. 
Bokeh refers to the fuzzy, out-of-focus background effect that results from using a fast lens and the widest aperture while photographing a subject. Therefore, bokeh is the appealing or aesthetically pleasant aspect of out-of-focus blur in a shot.

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Motion Blur
A motion blur effect is created when a fast-moving object is photographed with a slow shutter speed, making the object’s motion and surrounding area look streaked or smudged.
In CGI, motion blur has to be applied to the images, much like depth-of-field, ideally in conjunction with assessing both the camera’s and the object’s motions. Motion blur and grain are arguably the most common artefact of film recording.