Image signal processing apparatus, image signal processing method and camera using the image signal processing apparatus

• US 7,750,955 B2
• Filed: 08/29/2005
• Issued: 07/06/2010
• Est. Priority Date: 08/31/2004
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Shirai, Takahiro, Yoshida, Daisuke
• Primary Examiner(s): Ometz; David L
• Assistant Examiner(s): Spinks; Antoinette T
• Application Number:
  US11/212,636
• Publication Number:
  US 20060044424A1
• Time in Patent Office: 1,772 Days
• Field of Search: 348/243, 348/241, 348/251, 382266-275
• US Class Current: 348/243
• CPC Class Codes: H04N 25/677 for reducing the column or line fixed pattern noise

Abstract

When clamping a signal from a solid state image sensor, float of an optical black pixel output due to incoming of infrared light avoids a malfunction of a clamp from occurring. When clamping a signal from the solid state image sensor, the difference between the optical black pixel output and a clamp target level is output as a difference output, the difference output is compared with a comparison level to integrate the number of times larger than the comparison level every horizontal line. When the number of times is equal to or more than a certain rate (⅔) from the number of optical black pixels on the horizontal line, an optical black float state is determined and clamping operation is performed in accordance with a held value immediately before.

Claims

1. An image signal processing apparatus for subjecting to processing an image signal from a solid state image sensor having a plurality of effective pixels and a plurality of light shielded pixels, comprising:

averaging means for calculating and outputting average values of signals from the light shielded pixels and holding the calculated average values;

adding means for providing an output signal level obtained by superimposing a set threshold value, for determining whether a signal from the light shielded pixel is at an abnormal level or not, on the average values held by the averaging means;

comparing means for comparing the level of the signal from the adding means with levels of the signal from the light shielded pixels; and

clamping means for adjusting signals from the light shielded pixels to a predetermined level in accordance with the average value calculated by the averaging means,

wherein signals from the light shielded pixels or the average values held by the averaging means are selectively supplied to the averaging means in accordance with a comparison result by the comparing means, and

wherein, when the difference between the average value held by the averaging means and the level of signals from the light shielded pixels is larger than the set threshold value as determined by a comparison by the comparing means, the average value previously held by the averaging means is supplied to the averaging means instead of the signals from the light shielded pixels, and the signals from the light shielded pixels are provided to the average means instead of the average value previously held by the averaging means when the difference between the average value held by the averaging means and the level of signals from the light shielded pixels is smaller than the set threshold value as a result of comparison by the comparing means.

2. The image signal processing apparatus according to claim 1, wherein

the averaging means includes average value calculating means for calculating and outputting the average value of signals from the light shielded pixels and average storing means for storing the average value calculated by the average value calculating means.

3. The image signal processing apparatus according to claim 1, wherein

the clamping means adjusts signals from the light shielded pixels to a predetermined level in accordance with the difference between the average value calculated by the averaging means and a predetermined clamp setting level.

4. The image signal processing apparatus according to claim 1, wherein the apparatus is incorporated in a camera that includes:

a lens for imaging an optical image on a solid state image sensor; and

a diaphragm for changing the light quantity passing through the lens.

5. An image signal processing method for subjecting to processing an image signal from a solid state image sensor having a plurality of effective pixels and a plurality of light shielded pixels, comprising:

an averaging step of calculating and outputting average values of signals from the light shielded pixels and holding the calculated average values;

an adding step for superimposing a set threshold value, for determining whether a signal from the light shielded pixel is at an abnormal level or not, on the average values held in the averaging step, and for outputting a signal of a level based on a result of the adding step;

a comparing step of comparing the level of the signal outputted in the adding step with the level of signals from the light shielded pixels; and

a clamping step of adjusting signals from the light shielded pixels to a predetermined level in accordance with the average value calculated in the averaging step,

wherein the average values held in the averaging step are then selectively supplied in the averaging step, instead of signals from the light shielded pixels used for the averaging step, in accordance with a comparison result in the comparing step, and

wherein, when the difference between the average value held by the averaging step and the level of signals from the light shielded pixels is larger than the set threshold value as compared by the comparing step, the average value previously held by the averaging step is supplied to the averaging step instead of the signals from the light shielded pixels, and the signals from the light shielded pixels are provided to the average step instead of the average value previously held by the averaging step when the difference between the average value held by the averaging step and the level of signals from the light shielded pixels is smaller than the set threshold value as a result of comparison by the comparing step.