Image analysis – Color image processing
Reexamination Certificate
1997-04-09
2001-07-31
Mehta, Bhavesh (Department: 2721)
Image analysis
Color image processing
Reexamination Certificate
active
06269180
ABSTRACT:
The present invention relates to processing image data in order to facilitate composting and editing.
INTRODUCTION
The processing of broadcast quality video signals in the digital domain has become increasingly popular and has created a significant number of new production techniques. By using fast digital frame stores and parallel disk drives it is possible to produce full bandwidth digital video signals in real-time, thereby facilitating on-line video editing and compositing. This has led to a demand for such techniques to be used in cinematographic film editing, although the editing of cinematographic film is significantly more difficult given the relatively high information content of film compared to broadcast quality video.
In order for images conveyed by film media to be processed using digital techniques, it is necessary to scan the image frames to produce manipulatable digital image signals. After manipulation, these digital signals are supplied to an exposing device, arranged to expose destination film stock, thereby returning the manipulated image back onto a film medium. From the film viewer's point of view, a manipulated film image should be indistinguishable from an unmanipulated film image.
One area in which there is a problem of being able to distinguish between a manipulated film image and an unmanipulated film image, is where a film clip comprises a plurality of film image frames, each made up of a film image and a video or computer generated image. For example, where a video image or computer generated image of a foreground feature is composited with a filmed image of a background feature, there may be a mismatch in the textural qualities between the foreground image and the background image due to the “graininess” of the film image. The video or computer generated portion of the composite image can lack graininess or noise, or have a different noise characteristic to the portion of the composite clip which originated as a filmed image.
The graininess of a film is a visual sensation experienced by a viewer of the film, in which the viewer experiences a subjective impression of a random dot-like textural pattern in an image. When an image is projected onto a large area screen, the graininess of a filmed image may be readily apparent.
Graininess in a viewed film clip results from the physical composition of the film itself. Motion picture films consist of silver halide crystals dispersed in a gelatin emulsion. The exposure and development of the crystals form the photographic image, which is made up of the discrete particles of silver. In color processes, the silver is removed after development of the film, and dyes form dye clouds centered on sites of developed silver crystals. The crystals can vary in size, shape and sensitivity to light, and are generally randomly distributed within the emulsion.
Individual silver particles can range from about 0.002 mm, down to about 0.0002 mm. In a motion picture, the eye cannot distinguish individual grain particles, however the particles resolve into random groupings of dense and less dense areas which, when viewed, result in the visual sensation of graininess.
FIG. 1
of the accompanying drawings illustrates clouds of dye formed at sites occupied by exposed silver halide.
FIG. 2
of the accompanying drawings shows discrete grains at a magnification of around 400×. Grains nearer the surface of the film are in focus, whilst grains deeper in the emulsion are out of focus.
FIG. 3
of the accompanying drawings shows the make up of individual grains of filamentary silver enlarged by an electron microscope.
It is known for suppliers of particular film types to produce sets of curves characterizing the graininess of a batch or type of film in terms of the “granularity” of the film. A statistical measure of the granularity of a sample may be supplied by the film manufacturers in the form of an RMS granularity characteristic measured by an electro-optical microdensitometer.
However, an RMS granularity characteristic of a batch of film, or film type, may become inaccurate, due to factors such as temperature, the aging of film, exposure levels and other factors. A knowledge of the RMS granularity of the film on which a particular film clip is recorded will often not give an accurate enough basis for matching the granularity of an individual film clip.
SUMMARY OF THE INVENTION
According to the first aspect of the present invention, there is provided a method of processing image data, comprising steps of identifying a region of substantially constant color within a first image; analyzing color variation within said region; and applying a similar level of variation to a second image.
Preferably, a plurality of regions are selected, wherein each of said regions has a different color. In a preferred embodiment, mean or average values are calculated for the intensities.
In a preferred embodiment, standard deviation values are calculated for the intensities and these values may be considered as a function with respect to color. Preferably, the step of applying a similar level of variation to a second image involves applying a similar standard deviation to areas within said second image.
According to a second aspect of the present invention, there is provided an image data processing apparatus, comprising identification means configured to identify a region of substantially constant color within a first image; analyzing means configured to analyze color variation within said region; and applying means configured to apply a similar level of variation to a second image.
In a preferred embodiment the identification means is configured to identify a plurality of regions of differing colors and said analyzing means may be arranged to calculate mean or average values for said color variations. Preferably, the analyzing means is configured to calculate standard deviation values and said deviation values may be calculated with respect to each color.
In a preferred embodiment, the analyzing means analyzes standard deviation values of said first image and said applying means is configured to apply similar degrees of standard deviation to said second image.
Means may be provided for deriving the first image from cinematographic film. Means may be provided for deriving said second image from video data or, alternatively, a computer may be configured to generate said second image.
In a preferred embodiment, the analyzing means is configured to analyze a plurality of regions by traversing linearly across the first image.
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MacPherson Alan
Mehta Bhavesh
Millers David T.
Patel Kanji
Skjerven Morrill & MacPherson LLP
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