Method and/or apparatus to improve the visual perception of an image displayed on a screen

• US 8,144,107 B2
• Filed: 02/03/2006
• Issued: 03/27/2012
• Est. Priority Date: 02/16/2005
• Status: Active Grant

• Current Assignee: Sim2 Multimedia Spa (Finsim SRL)
• Original Assignee: Sim2 Multimedia Spa (Finsim SRL)
• Inventors: Toffoli, Domenico, Raffin, Mario
• Primary Examiner(s): Mengistu, Amare
• Assistant Examiner(s): Bolotin, Dmitriy
• Application Number:
  US11/795,706
• Publication Number:
  US 20080191996A1
• Time in Patent Office: 2,244 Days
• Field of Search: 345/84, 345/87, 345/89, 345/102, 345211-214
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2320/066 for control of contrast
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336

Abstract

The invention relates to a method and/or apparatus to improve the visual perception of an image displayed on a liquid crystal (LCD) panel, said method comprising steps for generating an adjusting signal (P_E,i+1) of a rear-lighting lamp of said panel depending on an target power value (P_T) and for generating a control signal (C_E,i+1) of the image contrast depending on said adjusting signal (P_E,i+1) of the rear-lighting lamp so as to increase/decrease the contrast of the displayed image when said adjusting signal (P_E,i+1) of the rear-lighting lamp decreases/increases.

Claims

1. Method for improving the visual perception of an image displayed on a liquid crystal screen, said method comprising at least steps for:

generating an effective adjusting signal (P_E,i+1) of a rear-lighting lamp depending on the value of a target power value (P_T) of said rear-lighting lamp; and

generating an effective image contrast control signal (C_E,i+1) depending on said effective adjusting signal of the rear-lighting lamp, so as to, increase, respectively decrease, the contrast of the image displayed on said screen as said effective adjusting signal (P_E,i+1) of the rear-lighting lamp decreases, respectively increases;

wherein said target power value (P_T) of said rear-lighting lamp is calculated as a function of the average of the mean luminances (S_i/2^N) of a predetermined plurality of previous image frames if the distance (d_i) between the mean luminance (y_i) of a current image frame (H) and the average of the mean luminances (S_i/2^N) of said predetermined plurality of previous image frames is less or equal to a threshold value (t_L), otherwise said target power value (P_T) of said rear-lighting lamp is calculated as a function of the mean luminance (y_i) of said current image frame (H) and the mean luminance of said predetermined plurality of previous image frames is initialized to the mean luminance (y_i) of the current image frame (H).

2. Method according to claim 1, wherein said target power value (P_T) is defined according to a table obtained empirically through observation of a plurality of scenes having different brightness.

3. Method according to claim 1, wherein said threshold value (t_L) allows to discriminate the scenic contents of a plurality of image frames (H).

4. Method according to claim 1, wherein said effective signals for adjusting the rear-lighting lamp (P_E,i+1) and for controlling the contrast (C_E,i+1) are generated at predetermined time intervals.

5. Method according to claim 4, wherein said time intervals are of 200 ms.

6. Method according to claim 1, wherein said effective contrast control signal (C_E,i+1) is made up of a first addend (C_ut,i), adjustably determined by an user, and a second variable addend depending on said effective power signal (P_E,i+1) for adjusting the rear-lighting lamp.

7. Method according to claim 6, wherein said second variable addend is given by the formula

k_c×

[1−

P_T,i/100]

wherein the constant k_c is determined by imposing that the light emitted by said liquid crystal screen at a given level of grey remains constant as the effective adjusting signal (P_E,i+1) of the rear-lighting lamp and the contrast control signal (C_E,i+1) change, thereby recovering the brightness lost when reducing the power of said rear-lighting lamp.

8. Apparatus for improving the visual perception of an image displayed on a liquid crystal screen, comprising:

circuit means (17) for generating an effective adjusting signal (P_E,i+1) of a rear-lighting lamp depending on the value of a target power value (P_T) of said rear-lighting lamp;

said circuit means (17) for generating an effective image contrast control signal (C_E,i+1) depending on said effective adjusting signal (P_E,i+1) of the rear-lighting lamp, so as to increase, respectively decrease, the contrast of the image displayed on said screen as said effective adjusting signal (P_E,i+1) of the rear-lighting lamp decreases, respectively increases;

wherein said apparatus further comprises;

calculation means (5, 7, 9, 11) for calculating the average of the mean luminances (y_i) of a predetermined plurality of previous image frames;

calculation means (4, 13, 15) for calculating the distance (d_i) between the mean luminance (y_i) of a current image frame (H) and said average of the mean luminance (S_i/2^N) of said predetermined plurality of previous image frames; and

circuit means (17) for calculating said target power value (P_T) of said rear-lighting lamp as a function of said average mean luminances (S_i/2^N) of said predetermined plurality of previous image frames if said distance (d_i) is less or equal to a threshold value (t_L) otherwise for calculating said target power value (P_T) of said rear-lighting lamp as a function of the mean luminance (y_i) of said current image frame (H) and for initializing the mean luminance of said predetermined plurality of previous image frames to the mean luminance (y_i) of the current image frame (H).

9. Apparatus according to claim 8, wherein said calculation means (4, 5, 7, 9, 11, 13, 15) and said circuit means (17) are implemented in a dedicated microprocessor of said apparatus.

10. Liquid crystal panel and/or screen comprising an apparatus according to one of claim 8 or 9.