Method for increasing the contrast of a synthetic image generator, and generator for the implementation thereof

• US 5,426,724 A
• Filed: 03/09/1992
• Issued: 06/20/1995
• Est. Priority Date: 03/12/1991
• Status: Expired due to Fees

• Current Assignee: Thomson-CSF
• Original Assignee: Thomson - Csf
• Inventors: Couturier, Alain
• Primary Examiner(s): Jankus, Almis R.
• Application Number:
  US07/848,305
• Time in Patent Office: 1,198 Days
• Field of Search: 395/119, 395/126, 395/129-132, 351/36, 382/22, 358/29, 358/78, 358/108, 358/461, 358/168, 358/169, 348/708, 348/712, 348/713
• US Class Current: 345/617
• CPC Class Codes: H04N 5/20 Circuitry for controlling amplitude response

Abstract

In order to improve the contrast of a synthetic image generator, the usually implemented operations of luminance compression are eliminated. Instead, a computation of true luminosity is made and the function of adaptation of the eye is included by computing the true output light energy. Then, the video components of the signal are sent to a display system and are standardized as a function of the light energy of the image displayed and the possible range of the image display. The method includes producing images with a luminance range substantially equal to the true luminance range of an eye and sending this signal to the display system. The signal is varied for different images at a time equal to the time an eye adjusts to different images. The apparatus includes a main channel being corrected by a computing circuit, having a peak luminance extraction circuit and a light energy computing circuit for generating a luminance correction signal.

Claims

1. A synthetic image generator producing synthetic images corresponding to actual images obtained from a video input and having improved contrast, comprising:

a main channel without luminance compression; and

a correction computing circuit adjusting luminosity of the main channel according to a luminance range perceived by an eye observing the actual images, wherein the correction computing circuit includes a peak luminance extraction circuit and a light energy computing circuit.

2. A generator according to claim 1, wherein the correction computing circuit includes a low-pass filter.

3. A method to improve contrast of an actual image obtained from a video input processed by a synthetic image generator, comprising the steps of:

processing said actual image to obtain an improved contrast synthetic image having a luminance range equal to a luminance range perceived by an eye observing the actual image; and

sending an image display signal representing an instantaneous luminance range of the actual image to an image display system, the image display signal being equal to a static luminance range of the eye when it observes static images, wherein the image display system varies the instantaneous luminance range with time at a rate no greater than the rate at which the eye adjusts to different luminances.

4. A method according to claim 3, applied to a multichannel display system, wherein all channels are each sent a control signal the instantaneous luminance range.

5. A method according to claim 3, wherein said control signal is taken at one of the channels serving as a reference channel.

6. A method according to claim 3, wherein the reference channel is chosen as a function of criteria selected from the group consisting of:

maximum peak value of white, predetermined fixed channel, channel corresponding to the axis of observation of the eye, and a greater mean value of luminosity.

7. A method to improve contrast of an actual image obtained from a video input processed by a synthetic image generator, comprising the steps of:

computing data of an image stored in a central data bank using a computation system which processes the data of the image on the basis of information elements relating to luminosity components of different channels of the image, colorimetrical components with relating to surface information and special effects elements, the computation system outputting a computed output signal;

extracting a peak luminance from the computed output signal using a peak luminance extraction circuit;

computing light energy from the computed output signal using a light energy computation circuit;

producing a first correction signal based on the computed output signal, the peak luminance and the light energy;

computing correction signals including the first correction signal and other correction signals corresponding to other channels of the image, for producing a common correction signal on the basis of mean contrast characteristics of the synthetic image generator and an information element corresponding to scotopic and photopic vision characteristics, the common correction signal correcting luminance of the image; and

simulating a rate for computing the correction signals no greater than a rate at which an eye accommodates to changes in luminance;

combining the common correction signal with the computation output signal to provide a corrected output signal representing the synthetic image with proper luminance.

8. A method according to claim 7, further comprising the steps of:

gamma correcting the corrected output signal; and

sending the correction signal (K) to other video processors for computation of a correction signal on other channels.

9. A method according to claim 7, wherein the simulating step is performed by a multiplexer-adder followed by a low-pass filter.

10. A synthetic image generator improving the contrast of an actual image obtained from a video input, comprising:

a mode selection circuit for selecting between mean, peak and local luminance modes, and for outputting a luminance and chrominance signal (LC) based on information elements relating to the desired contrast (CONT) and information elements on the general conditions of illumination (JCN);

a plurality of processors in parallel receiving a selected mode from the mode selection circuit, each processor processing image data for different channels, for a processing image data on a channel; and

multipliers receiving the luminance and chrominance signal (LC), each of the multipliers receiving an output signal from one of the processors and combining the output signal with the luminance and chrominance signal (LC) for simulating the criterion of integration of an eye, such that a contrast on any one channel does not cause different channels to lose contrast.