DISPLAY PROCESSING APPARATUS FOR MIXING VIDEO AND GRAPHICS IMAGES WITH SEPARATE COLOUR CONTROLLERS

Abstract: When PC graphics and video are keyed or mixed to be displayed on a common display, different optimum colour temperatures and white levels of the different sources may compromise the picture quality. The invention controls the relative and absolute amounts of the colour components separately for the two sources, by the use of variable gain amplifiers, prior to keying or mixing. This compensates for different optimum colour temperatures and white levels and results in better picture quality.

Description: DISPLAY PROCESSING APPARATUS FOR MIXING VIDEO AND GRAPHICS IMAGES WITH SEPARATE COLOUR CONTROLLERS This invention relates to display processing. There are a multitude of applications in which it would be desirable to mix outputs from graphics and video sources on a common display. Clearly, problems will arise from differing refresh rates and line structures of the various sources and reference is directed to EP 0 696 401 which discloses display up-conversion techniques by which video signals may be upconverted to a form permitting mixing with conventional PC graphics outputs. In addition to problems with different refresh rates and line structures, various sources generally differ in their composition of colour components. It is to be understood that the composition of the colour components determines the colour temperature as well as the intensity of the white level of a source. PC graphics monitors are frequently set up for 9600K colour temperature, which gives a blue-white light. For improved visual acuity, the light spectrum should include less blue and more red, so a lower colour temperature is beneficial. 5400K is a colour temperature that is becoming popular. It allows better visibility of text without eye strain, and allows higher brightness of peak white without blooming. Video material is produced for use with displays of very particular characteristics. The spectral peaks of the three (red, green and blue) components of the display are defined, as are the proportions of the three components that make up the correct white, which has a colour temperature of 6500K. As mentioned above, the composition of the colour components also determines the intensity of the white level. It is not unusual for a PC screen to be predominantly white, with small areas of black text. This text must be clearly readable, so the level of acceptable blooming (loss of focus in white areas) is very low. Television pictures on the other hand, very rarely have significant white areas. They are more typically composed in such a way that the areas of interest are lit and shot to be in the mid-grey region, and white is used as a high light, for artistic effect. This means that the acceptable level of blooming is considerably higher than for PC graphics. If television displays are set at a brightness and contrast level for minimal blooming, they can be unacceptably dim for optimal viewing. Previous approaches have compromised quality in one or both of the video or graphics images to achieve mixing. It is an object of the present invention to provide still further improved display processing which enables the mixing of video and graphics material with minimal compromise. Accordingly, in one aspect, the present invention consists in apparatus for display processing, comprising at least two channels, each for receiving displayable material, and a mixer adapted to combine the outputs of the channels to drive a display; characterised in that a separate colour temperature controller is provided in at least one of the channels. In a further aspect, the present invention consists in a method for display processing, in which material from two or more sources is mixed to drive a display; characterised in that differential colour control is provided between the material from the sources. It has been recognized that PC graphics output and video material are customarily viewed with different colour temperatures and peak white intensities. When the PC graphics and television pictures share the display, for example when a keying, mixing or fading process is used between the two sources for high quality multimedia display, the differences in colour temperature and white level cannot be programmed into the display in the normal way, but must be controlled electronically before the keying process. The invention will now be described by way of example, with reference to the accompanying drawing in which Figure 1 is a block diagram of display processing apparatus according to the present invention. It will be observed that the output from a PC source 1 and a video source 2 both pass through a respective colour controller 3, 4 before being mixed or keyed in mixer 5 before passing to the display 6. Each colour controller 3, 4 enables separate control over the gain of R, G, and B signals. It will be understood that it is by varying the relative amounts of R, G and B that the display colour temperature is selected, and by varying the amounts of the R, G and B together that the peak white level is adjusted. In a preferred embodiment, each of the six signals (R, G and B for each of the PC and video signals) is controlled by a variable gain amplifier. These amplifiers can be voltage controlled or numerically controlled. If they are voltage controlled, the control voltages can be generated by digital to analog converters (DACs) . Either way, a remote numerical controller, such as a PC with the appropriate software or an embedded controller, can modify the colour temperatures and peak white levels under instruction from a user, an automatic control program, etc. In a simplified version, the colour controller 3, 4 controls only one or two of the R, G and B components. For example, the colour controller 3, 4 may comprise one or two variable gain amplifiers. If appropriate, the control may take place in a matrix operation dedicated to the process or additionally serving another purpose. In a variation, the desired colour control for the two sources may be achieved by providing a controller 3, 4 in one channel only, with an optional controller of the mixed output. It should be understood that video and graphics have been selected as examples of materials which are required to be mixed and which have different optimal colour temperatures or white levels. The invention is not restricted in this regard and extends to sources in different number and of different nature.

Claims: CLAIMS 1 . Apparatus for display processing, comprising at least two channels, each for receiving displayable material, and a mixer adapted to combine the outputs of the channels to drive a display; characterised in that a separate colour controller is provided in at least one of the channels. 2. Apparatus according to Claim 1 , wherein the channels comprise one channel for receiving graphics material and one channel for receiving video material. 3. Apparatus according to any preceding claim, wherein the colour controller controls the amounts of R, G and B components of the displayable material. 4. Apparatus according to any preceding claim, wherein the colour controller comprises at least one variable gain amplifier. 5. Apparatus according to any preceding claim, wherein the colour controller comprises three variable gain amplifiers. 6. Apparatus according to any preceding claim, wherein a separate colour controller is provided in every channel. 7. A method for display processing, in which material from two or more sources is mixed to drive a display; characterised in that differential colour control is provided between the material from the sources. 8. A method according to Claim 7 wherein the material from one source comprises PC graphics material and the material from the other source comprises video material. 9. A method according to Claim 7 or Claim 8, wherein said colour control is effected through control of the amount of R, G and B components of the material. 10. A method according to Claim 7, 8 or 9, wherein individual colour control is provided for the material from each of said sources.

Inventors: SETH-SMITH NIGEL, SETH-SMITH, NIGEL
Applicants: SETH SMITH NIGEL, SNELL & WILCOX LTD, SETH-SMITH, NIGEL, SNELL & WILCOX LIMITED
Application year: 1998
Main classification: G09G5
IPC codes: G09G5