GB2410804A

GB2410804A - Image processor with light intensity modifying means

Info

Publication number: GB2410804A
Application number: GB0402703A
Authority: GB
Inventors: David William Macintosh
Original assignee: ACCUSCENE CORP Ltd
Current assignee: ACCUSCENE CORP Ltd
Priority date: 2004-02-07
Filing date: 2004-02-07
Publication date: 2005-08-10
Also published as: GB0402703D0

Abstract

An image processing system for receiving a electronic image has a means for determining the light intensity of individual or groups of picture elements (e.g. pixels) with the image. A determining means determines whether the picture element needs to be modified depending on the light intensity in respect to pre-determined thresholds or mapping tables. Modification is only necessary if the light intensity is at or near the extremes of the available range or greyscale. If modification is made the picture element is replaced and transmitted. The system may be used with an image display, an electronic viewfinder or a monitor display a recording and/or printing system.

Description

241 0804

Description

FIELD OF THE INVENTION

The invention relates to the field of image processing and, more specifically, to systems and products intended to provide clear feedback to the operator of use of available dynamic range and of focus setting and depth of field within images or series of images being processed by said systems and products

BACKGROUND OF THE INVENTION

All image processing systems and products such as cameras, displays, printers and storage devices have inherent limitations as to the dynamic range they can handle. Available contrast ratio, or dynamic range, between the light intensity of white and black areas in the image being processed is determined both by the range and resolution of numerical or other quantities carrying information comprising the image. It is also limited by the performance of the media involved in capturing, transmitting, displaying, storing and if required, printing the image.

In capturing and processing images in all fields of photography including cinematography and medical imaging the operator requires certain knowledge of whether the image being captured or processed is optimally utilising the available dynamic range of the equipment involved, since it is usually the case that the real world, or the possible outcomes of an image processing operation, can and does carry information beyond the available dynamic range Operator choices or adjustments such as the shutter speed or lens aperture of a camera, or the resolution or exact process algorithm of an image processing system, can influence the quality of the resultant image It is a known factor of human eyesight that small differences are not easily detected in nearly-black or nearly- white images and therefore the operator may not be aware by inspection of the actual images that compression is nearly or actually happening. In professional cinematography it remains usual practice to monitor the output from the camera with equipment such as a waveform monitor to ensure that no compression (limiting against either the black or the white endpoints of the available system dynamic range) and to make manual adjustments of exposure to optimise use of the available dynamic range Subsequently, in grading or post-production processes, individual images or series of images are manipulated to normalise their appearance. Again, close attention to ensure that compression is avoided is required.

An addition and simultaneous requirement for the optimum operation of a camera is the setting of focus of a lens or other means of gathering and presenting light from the field of view to a sensor or light-sensitive film. Present means to provide feedback of focus to a camera operator or system setting focus in an automated or semi-automated fashion involve the detection of edges or boundaries between dissimilar areas within a field of view Techniques such as 'Peaking' in professional electronic stills or video cameras provide the means of highlighting detail within the field of view, to provide the operator with feedback as to the range of focus of the camera. Unfortunately where the field of view contains either low-contrast or high-contrast images the Peaking function tends to provide either too little or too much feedback reducing its effectiveness in providing useful feedback The present invention artificially highlights only the extreme ends of the available dynamic range of intensity to provide clear and unambiguous feedback to the operator as to the extent to which his or her current image, while in process or while being captured by the camera, approaches the limits of system dynamic range. The key to providing clear feedback in the present invention is that it does not affect the bulk of the content of an image and thereby can be used in real time and on-line, since the operator can continue to perform other functions such as monitoring image content and focus while applying the present invention. The provision of unambiguous feedback is achieved through intuitive use of pseudo-colour to differentiate near- blacks and near-whites with the current image to be captured by the sensor or light-sensitive film The invention does not merely mark areas at the boundaries of the dynamic range of the system, but provides a number of contours or levels of marking approaching these limits, so the operator is presented with pseudo-colour information within the normal range of exposure of the camera or image capture or processing system, thereby providing useful feedback regarding exposure and focus at the extremes of intensity within a desired image A second benefit of thus marking areas of or approaching extreme intensity is to provide feedback as to the focus of a camera. As areas of extreme intensity within the field of view of a camera are brought into sharper focus, the contours of pseudo-colour become progressively more defined and contained, the opposite is true when areas of extreme intensity are less sharply focused as they become more diffuse and less extreme in intensity as presented to the imager or light-sensitive film. Because the invention highlights only those areas of extreme intensity, and their intensity is also a function of focus or of depth of field, the invention simultaneously provides an operator with intuitive feedback as to the sharpness

of focus within these areas of the field of view.

A different approach to providing a camera operator with feedback as to exposure - or use of available system dynamic range - employing pseudocolour is described in US Pat. No. 5,041,911 entitled "Exposure information feedback in electronic and/or hybrid film/electronic cameras" by Michael C. Moorman. In this approach information in the current image is chapped to pseudo-colour steps collesponding to stops of exposure. An alternative described in this approach is to mark 'either severely underexposed or overexposed individual or groups of picture elements or pixels (outside of the dynamic range of the photographic system being used)'.

SUMMARY OF TO INVENTION

In contrast to the Moorman approach, the present invention provides only the crucial information an operator requires to allow optimum use of the available system dynamic range and to avoid saturation. Only those individual or groups of picture elements or pixels that are nearly at the extremes of available system dynamic range are marked The remainder usually the bulk of the image - is left untouched.

Employment of pseudo-colour to represent values within an image or a signal carrying an image is well known and while utilised as a convenient means of marking, does not comprise part of the present invention. An example of this use is described in US Pat. No. 4,011,584 entitled "System for color presentation of information represented by amplitude varying video signal" by Lawrence C. Puckett The preferred embodiment of the present invention is comprised of an image processing system interposed between a compatible image source and a suitable image destination, such as a camera driving a display monitor or a recorder. Within the image processing system images being transmitted through it are monitored and modified, when' - ,-,aired, to highlight individual or groups of picture elements or pixels whose Jight intensity is nearly at the extremes of available system dynamic range. An intuitive set of pseudo-colours may be employed to mark such pixels by overlaying their original luminance value In monochrome with a colour corresponding to the nearest band as shown in (Figure 1) Note that between 20% and 80%, pixel data are unchanged, preserving the bulk and normally most sgrnficant content of the image The percentage figures shown in Figure 1 denote the available system dynamic range, often (for Instance, In the case of high-definition or standard-definition video) stated to conform Rhythm a range of 0 ' 10% to allow for 10% highlights above nominal white. The tri-colour GB values shown withy the pseudo-colour ranges exemplify the pseudo-colours that may be employed to denote certain bands against available system dynamic range. Therefore pixels marked as yellow are at or near the nominal maximum signal level, 100%. Orange- or red-marked pixels lie above this range.

It will be appreciated by one practiced in the field that the preferred embodiment is only one specific example of the principle of the application of the present invention, whose unique and trmovative step is to show the majority of an image unchanged while applying pseudo- or false-colour to differentiate and identify only extremes of luminance within the image according to a desired set of conditions or limits suited to the particular application for which they are applied.

Claims

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Claims 1 An image processing system combination.

means within said image processing system for receiving an electronic image or series of images; means within said image processing system for determining or measuring the light intensity of individual or groups of picture elements or pixels within said electronic image or series of images; means within said image processing system for determining whether said individual or groups of picture elements or pixels should be left unmodified or of assigning synthesised colour or colours to said individual or groups of picture elements or pixels depending on their measured light intensity according to pre-determined light intensity thresholds or mapping

tables;

incorporation of pre-deter,rnined criteria within said light intensity thresholds or mapping tables whose application results in no modification of said individual or groups of picture elements or pixels unless their light intensity is at or near extremes of the available range or greyscale; means within said image processing system for modifying said image or series of images by replacing said individual or groups of picture elements or pixels according to said criteria where their light intensity is at or near extremes of the available range or greyscale and; means within said image processing system for transmitting said modified image or series of images
2. An image display system combination wherein individual or groups of picture elements or pixels within an electronic image or series of images are displayed comprising: a. an image processing system according to claim 1; b means to allow an operator to select or deselect a mode of operation within said image display system wherein said image processing system may apply the process of differentiating individual or groups of picture elements or pixels within an electronic image or series of images according to claim 1 prior to display and; c. means of displaying said electronic image or series of images with adequate range to maintain and show said differentiated individual or groups of picture elements or pixels
3. An electronic viewfinder system capable of displaying to an operator an electronic images or series of images captured or generated in real- time or retrieved from a image store comprising: a. an image display system according to claim 2 and; b. means to allow said electronic viewf nder to accept an electronic image or series of images output from a camera or other compatible image source 4 An electronic monitor display system capable of displaying to an electronic images or series of images captured or generated in real-time or retrieved from a image store comprising a an image display system according to claim 2 and; b means to allow said electronic monitor display system to accept an electronic image or series of images output from a camera or other compatible image source 5. An image recording and/or printing system capable of storing and/or reproducing an electronic images or series of images captured or generated in real-time or retrieved from a image store comprising: a. an image processing system according to claim 1 and; b. means to allow said recording and/or printing system to accept an electronic image or series of images output from a camera or other compatible image source c means of storing and/or reproducing said electronic image or series of images with adequate range to maintain and show said differentiated individual or groups of picture elements or pixels 6 Use of an electronic viewfinder system according to claim 3 to assist an operator to determine optimum exposure settings and / or focus in a camera or other image capture or processing system 7. Use of an electronic monitor display system according to claim 4 to assist an operator to determine optimum exposure settings and / or focus in a camera or other image capture or processing system 8 Use of an image recording and/or printing system according to claim 5 to assist an operator to determine optimum exposure settings in a camera or other image capture or processing system