1. Field of the Invention
The present invention relates to apparatus for processing image data, the method of processing image data and a computer-readable medium.
2. Description of the Related Art
Film editing and processing has historically been performed without the aid of digital image processing systems. In the past, the appearance of different film batches was controlled by a film colorist, whose job it is to ensure that when different film clips are spliced and edited together, their characteristics are not noticeably different. In order to achieve this, exposure times, negative types, and lighting conditions during a shoot have to be carefully controlled, and this is a highly specialised aspect of cinematography.
At the present time, increasing amounts of film editing and processing are being performed within a digital environment. The transfer of film processing to the digital domain has been relatively slow due to the enormous amounts of data that are required to be stored. Up to forty megabytes of data per frame of film is required in order to achieve equivalent film resolution in a digitised image. Slowly, however, as the cost of computer hardware and storage reduces, film processing is moving into the digital domain.
Once images have been digitised, it is possible to mix image data from a variety of formats, for example video mixed with film images, and to composite and edit these images together. It is known to imitate the film look by applying certain non-linear processing to video-sourced images, and so it may be possible to mix video and film images without the changeover being obvious between the two.
However, even though images can be freely mixed, composited and arranged in the digital domain, high quality editing still requires the same attention to detail that was performed by the film colorist. It is still necessary to control color matching between different image sources, whether they be from different reels of film, or from unrelated sources such as video. While it is widely known to employ controls such as contrast, color look-up tables, and various types of color manipulation, none of these methods provides an easy way of achieving a color match between images. A skilled colorist may be able to manipulate known systems in order to achieve a high degree of color matching. However, this remains a skilled and time consuming job. It is also a task that needs to be performed many times within a typical editing session.
According to an aspect of the present invention, there is provided apparatus for processing image data, including memory means for storing image data and processing instructions, and processing means for performing said image processing, wherein said instructions define operations to be performed by said processing means in order to process said image data, and said processing means is configured by said instructions such that: an input image is to be matched with a reference image, an initial output image has been generated from said input image and a matching transformation for processing image data has been initialised; and said operations include repeated steps of: identifying a first region in said output image and a reference image in said reference image, wherein said regions have a similar characteristic; comparing said regions to identify a difference transformation for said output image; updating said matching transformation by applying said difference transformation to it; and processing said input image with said matching transformation to update said output image.