Digital image picture frame with self-adaptive control of brightness level
View Patent ↗The picture frame comprises: a decorative frame ( 18 ), support or hanging means ( 22, 24 ), a display screen ( 12 ), a driver circuit ( 46, 48 ) for driving the screen, and a processor ( 32 ). It further includes wireless interface means ( 34 ), in particular of the Bluetooth type, for interfacing with a remote appliance such as a mobile telephone in order to receive therefrom digital image data blocks, each corresponding to an image for storing in a memory ( 40 ) and for displaying on the display screen. In the event of a change in the state of a change of a screen orientation sensor ( 50 ), the processor applies pivot processing to the image data so as to restore the initial orientation of the displayed image. The picture frame also includes self-adaptive means for controlling its brightness level and suitable for detecting and storing successive changes of state in a sensor and for extrapolating from said changes an automatic control relationship for controlling the brightness level of the screen.
1. A method for automatically controlling the on/off switching of a display screen of a picture frame for digital photographic images, wherein the picture frame comprises:
a display screen suitable for displaying an image in the form of a matrix of pixels;
a driver circuit for driving said display screen;
processor means suitable for delivering image data to the driver circuit for display on said display screen;
memory means for storing image data blocks and co-operating with said processor means;
means for lighting said display screen; and
means for automatically controlling the brightness level of said screen, including a sensor for sensing an ambient lighting level;
wherein said method comprises:
a) determining at regular intervals successive mean values of said ambient lighting level;
b) determining a mean minimum value and a mean maximal value from said successive mean values over a pre-determined time period;
c) deriving from said mean minimum value and said mean maximal value a darkness-to-light transition threshold and a light-to-darkness transition threshold;
d) comparing the current ambient lighting level to said darkness-to-light and light-to-darkness transition thresholds;
e) switching on said display screen upon crossing of said darkness-to-light transition threshold and switching off said display screen upon crossing of said light-to-darkness transition threshold.
2. The method as in claim 1 , further comprising, following step a), performing a calibration stage when the frame is switched on for the first time or after the frame has been off for a period, said calibration stage comprising:
determining a dynamic range in lighting level between a mean minimum and a mean maximum of the lighting level;
comparing said dynamic range to a predetermined threshold;
if said dynamic range is greater that said predetermined threshold, confirming automatic control of the on/off switching of the display screen;
if said dynamic range is not greater that said predetermined threshold, deactivating said automatic control.
3. The method as in claim 1 , wherein said mean minimum value and mean maximal value are determined over a 30-minute time period.
4. The method as in claim 3 , further comprising a deglitching operation including replacing over each new daily period the three largest and the three smallest values of the 30-minute mean value by the three largest and the three smallest values of the day.
5. The method as in claim 1 , wherein said mean minimum value is the mean of the ten largest values of a 30-minute mean of said ambient lighting level, and said mean maximal value is the mean of the ten smallest values of said 30-minute mean of said ambient lighting level.
6. The method as in claim 1 , wherein said darkness-to-light transition threshold is different and higher than said light-to-darkness transition threshold, whereby minimizing the risk of oscillating between two states.
7. The method as in claim 6 , wherein the difference between said darkness-to-light and light-to-darkness transition thresholds is:
TDL−TLD =( NL MAX− NL MIN)*0.04
TDL being the darkness-to-light transition threshold,
TLD being the light-to-darkness transition threshold,
NLMIN being the mean minimum value, and
NLMAX being the mean maximum value.
8. The method as in claim 7 wherein said darkness-to-light and light-to-darkness transition thresholds are computed according to the following relationships:
TDL=NL MIN+( NL MAX− NL MIN)*0.06
TLD=NL MIN+( NL MAX− NL MIN)*0.02.
9. The method as in claim 1 , wherein said switching on of the display screen is performed only upon crossing of said darkness-to-light transition threshold for a minimum predetermined period of time and switching off of the display screen is performed only upon crossing of said light-to-darkness transition thresholds for the minimum predetermined time period.
10. The method as in claim 1 , wherein said current ambient lighting level to be compared to said darkness-to-light and light-to-darkness transition thresholds is evaluated from successive mean values that are calculated continuously.
11. The method as in claim 10 , wherein said successive mean values are calculated either over a first time period or over a second, different time period, selectively as a function of short-term variations in the lighting level.
12. The method as in claim 11 , wherein said first time period is a 2-second period and said second time period is a 20-second period.
13. The method as in claim 1 , further comprising:
detecting a manipulation of a button of the picture frame by a user, and
ignoring lighting level measurements taken during a period preceding and following said manipulation.