Method for the real-time processing of a signal representing an image

• US 7,440,011 B2
• Filed: 03/26/2003
• Issued: 10/21/2008
• Est. Priority Date: 03/29/2002
• Status: Expired due to Fees

• Current Assignee: Valeo Vision (Valeo SE)
• Original Assignee: Valeo Vision (Valeo SE)
• Inventors: Fleury, Benoist, Hue, David
• Primary Examiner(s): Ometz; David
• Assistant Examiner(s): PRABHAKHER, PRITHAM DAVID
• Application Number:
  US10/397,734
• Publication Number:
  US 20030184827A1
• Time in Patent Office: 2,036 Days
• Field of Search: 358/520, 348/222.1, 348/362, 348/235, 348/239, 348/229.1, 348/364, 348/221.1, 382/270
• US Class Current: 348/229.1
• CPC Class Codes: H04N 23/00 Cameras or camera modules comprising electronic image sensors; Control thereof
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene

Abstract

A signal representing an image generated by at least one photosensitive device is processed in real-time to supply, from a scene to be observed having a high dynamic range between the signals corresponding to the darkest areas and to the brightest areas, an image containing no blooming areas. Images of different sensitivities are formed from the same scene to be observed. The brightness level of each point on the most sensitive image is determined. This level is compared with a predetermined threshold. The signal of the most sensitive image is delivered to the display device, for each elementary point on the most sensitive image having a brightness level below the predetermined threshold. An image signal calculated according to the brightness levels of the same elementary point in the images of different sensitivities is delivered to the display device, for any other elementary point on the most sensitive image.

According to the present invention, images of different sensitivities are formed from the same scene to be observed, the brightness level of each elementary point on the most sensitive image is determined, this level is compared with a predetermined threshold, the signal of the most sensitive image is delivered to the display device, for each elementary point on the most sensitive image having a brightness level below the predetermined threshold, and an image signal calculated according to the brightness levels of the same elementary point in the images of different sensitivities are delivered to the display device, for any other elementary point on the most sensitive image.

Claims

1. Method for the real-time processing of a signal representing an image generated by at least one photosensitive device in order to supply, from a scene to be observed having a high dynamic range between signals corresponding to the darkest areas and those which correspond to the brightest areas, an image free from blooming areas, the method comprising the steps:

forming an actual image of the scene to be observed on the photosensitive device by an optical system,

controlling the photosensitive device to generate per second a first predetermined number of image signals of the scene to be observed,

collecting the image signals generated by the photosensitive device,

processing the image signals generated by the photosensitive device,

converting the processed signals into video signals,

delivering the video signals to a display device,

displaying on the display device a second predetermined number of images per second corresponding to the processed image signals,

the step of controlling the photosensitive device comprising the generation of image signals of the same scene to be observed with at least first and second different sensitivities, the first sensitivity being greater than the second,

the step of processing the signals generated by the photosensitive device itself comprises the steps;

determining the brightness level of each elementary point on the image having the first sensitivity and of each elementary point on the image having the second sensitivity, and

delivering to the display device for each elementary point on the final image an image signal calculated according to the levels of brightness of the same elementary point in the images of first sensitivity and second sensitivity,

wherein the method further comprises the steps;

comparing the brightness level of each elementary point of the image of first sensitivity with a predetermined threshold,

delivering to the display device, for each elementary point on the image of first sensitivity having a brightness level below the predetermined threshold, the signal of the image of first sensitivity, and

delivering to the display device, for any other elementary point on the image of first sensitivity, an image signal equal to a weighted sum of the brightness levels of the same elementary point in the images of first sensitivity and second sensitivity.

2. Method according to claim 1, wherein, for each elementary point on the image of first sensitivity whose brightness level is greater than or equal to the predetermined threshold, the brightness level of the signal delivered to the display device consists of approximately 30% of the brightness level of the image of second sensitivity and 70% of the brightness level of the image of first sensitivity.

3. Method according to claim 1, wherein the images of first and second sensitivities are obtained by distinct photosensitive devices.

4. Method according to claim 3, wherein the photosensitive devices are synchronized to supply image signals comprising a plurality of elementary points which can be matched both in time and in space.

5. Method according to claim 1, wherein the image signal processing step is performed only when the image of first sensitivity has blooming areas.

6. Method according to claim 5, wherein the brightness of the scene to be observed is measured by a detector.

7. Method according to claim 6, wherein the detector consists of a counter for the number of elementary points in the image of second sensitivity whose brightness is equal to a predetermined value.

8. A method for providing an image free from blooming areas, the method comprising:

obtaining an image of a scene to be observed on a photosensitive device;

generating per unit of time a predetermined number of image signals of the scene to be observed with at least first and second different sensitivities, the first sensitivity being greater than the second;

determining the brightness level of each elementary point on the image having the first sensitivity and of each elementary point on the image having the second sensitivity;

comparing the brightness level of each elementary point of the image of first sensitivity with a predetermined threshold; and

displaying an image signal calculated, for each elementary point of a final image, according to the brightness levels of the same elementary point in the images of first sensitivity and second sensitivity,

wherein the calculated image signal comprises the signal of the image of first sensitivity, for each elementary point on the image of first sensitivity having a brightness level below a predetermined threshold, and comprises an image signal calculated according to the brightness levels of the same elementary point in the images of first sensitivity and second sensitivity, for any other elementary point on the image of first sensitivity, and

wherein a function of the brightness level (N₃) of the elementary point of the final image corresponding to an elementary point on the image of first sensitivity having a brightness level that is above the predetermined threshold is of the form;

$N_3=N_2+\left(S_1-S_2\right)*\frac{\left(K-N_2\right)}{\left(K-S_2\right)}$

where;

N2 is the brightness level of the elementary point on the image of second sensitivity corresponding to an elementary point on the image of first sensitivity having a brightness level above the predetermined threshold,

S₁ is the predetermined threshold value for an elementary point on the image of first sensitivity,

S₂ is the brightness level of the elementary point on the image of second sensitivity corresponding to a point on the image of first sensitivity having a brightness level equal to S₁, and

K is a number of different brightness levels which the photosensitive device is capable of distinguishing.

9. A method for providing an image free from blooming areas, the method comprising:

generating at least two input image signals of a scene to be observed on at least one photosensitive device, the first input image signal having a first sensitivity greater than a second sensitivity of the second input image signal;

calculating output image signals based on brightness levels the two input image signals at corresponding elementary points; and

displaying the output image signals,

wherein, for each elementary point, a brightness level of the output image signals is calculated as follows;

(i) when a brightness level of the first input image signal is less than or equal to a predetermined threshold, the brightness level of the output signals is equal to a corresponding elementary point of the first input image signal,

(ii) when a brightness level of the first input image signal is equal to a maximum value, the brightness level of the output signals is equal to a corresponding elementary point of the second input image signal, and

(iii) when a brightness level of the first input image signal is between the predetermined threshold and the maximum value, the brightness level of the signal is calculated by a linear equation to be between the brightness levels of the corresponding elementary points of the first and second input image signals.

10. Method according to claim 9, wherein the linear equation is of the form:

$N_{\left(P_{3<br><br>\left(i,j\right)}\right)}=\left(N_{\left(P_{1<br><br>\left(i,j\right)}\right)}*\left(\frac{N_{\max }-N_{\left(P_{1<br><br>\left(i,j\right)}\right)}}{N_{\max }-N_s}\right)\right)+\left(N_{\left(P_{2<br><br>\left(i,j\right)}\right)}*\left(1-\frac{N_{\max }-N_{\left(P_{1<br><br>\left(i,j\right)}\right)}}{N_{\max }-N_s}\right)\right)$

where, for each pair of coordinates i and j of an elementary point;

P_1(i,j) is an elementary point on the image of first sensitivity,

P_2(i,j) is an elementary point on the image of second sensitivity,

P_3(i,j) is an elementary point on the image displayed on the display screen,

N_(P1(i,j)) is the brightness level of the elementary point P_1(i,j),

N_(P2(i,j)) is the brightness level of the elementary point P_2(i,j),

N_(P3(i,j)) is the brightness level of the elementary point P_3(i,j),

N_max is the maximum brightness level of the image of first sensitivity, and

N_s is the brightness level of the predetermined threshold.