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Illuminance compensation method and equipment in picture shoot

A technology of image capture and ambient temperature, applied in image communication, printing equipment, cameras, etc., can solve the problem of not considering the change of junction temperature

Inactive Publication Date: 2004-12-29
HEWLETT PACKARD CO
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

Another disadvantage of this method is that it does not account for changes in junction temperature during image capture

Method used

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  • Illuminance compensation method and equipment in picture shoot
  • Illuminance compensation method and equipment in picture shoot
  • Illuminance compensation method and equipment in picture shoot

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Embodiment Construction

[0016] FIG. 1 is a block diagram of a photographic exposure system 100 . A central processing unit (CPU) 110 sends an illumination control signal 116 to the LED driver 112 and the LED model 102 . LED driver 112 is connected to LED array 114 . LED array 114 provides illumination for capturing images. The shooting exposure system also has an ambient temperature sensor 106 . The output value of the ambient temperature sensor 106 is read by the A / D converter 104 and transmitted to the CPU 110. The non-volatile memory 102 is connected to the CPU 110 and stores calibration values ​​and long-term time-varying information. The counting timer 104 is also connected to the CPU 110 and records the on and off times of the LEDs.

[0017] The light output of an LED can be calculated using the experimentally derived figure of merit T with the help of the following equation 0 to describe:

[0018] LOP ( T j ...

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Abstract

The junction temperature of an LED is determined. This result is used to determine an initial brightness value of the LED. The initial brightness value is derated by a long-term degradation amount that is determined using a stored indication of the lifetime total on time. The derated brightness value is used to determine an exposure for a capture system. The junction temperature is determined by measuring the ambient temperature and then keeping a running junction temperature determined from the on and off times.

Description

technical field [0001] The present invention relates generally to precise control of exposure and, more particularly, to modeling the light output of LEDs to maintain constant exposure as the light output of the LED array varies with the temperature and age of the component. Change. Background technique [0002] High-quality image capture such as grayscale and color imaging requires precision light sources. Considering their size, price, performance, and other qualities, various light-emitting diodes (LEDs) can be selected as light sources for capturing images. Unfortunately, the light output of LEDs varies with junction temperature and age. Since LEDs heat up when energized, one of the factors that determines the junction temperature of an LED, and therefore its light output, is the amount of time the LED is energized and the duty cycle. One way to compensate for at least some of this variation is to use optical calibration tape. Light calibration strips can be used wit...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): G03B27/54G03B7/00G03B7/22H01L33/00H01L33/08H04N1/00H04N1/04H05B33/00H05B37/02
CPCH04N1/00002
Inventor P·A·博尔格K·福里斯特
Owner HEWLETT PACKARD CO