IMAGE SIGNAL PROCESSING APPARATUS, IMAGE SIGNAL PROCESSING METHOD AND CAMERA USING THE IMAGE SIGNAL PROCESSING APPARATUS

• US 20100231762A1
• Filed: 05/19/2010
• Published: 09/16/2010
• Est. Priority Date: 08/31/2004
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Shirai, Takahiro, Yoshida, Daisuke
• Granted Patent: US 8,223,228 B2
• Time in Patent Office: Days
• 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 applying processing to an image signal from a solid state image sensor having a plurality of effective pixels and a plurality of light shielded pixels, comprising:

an optical black level determining portion for comparing optical black output from the light shielded pixel with a predetermined clamp level and outputting as difference outputs a difference between the optical black output and the predetermined clamp level;

a holding portion for holding the difference output;

an adding and subtracting circuit for clamping image signal in accordance with the difference output;

a comparator for comparing the difference output of the pixel with a predetermined comparison level; and

a counter portion for counting the number of times when the difference outputs are larger than the comparison level;

wherein

when the number of times exceeds the predetermined number of comparison times, the already held difference output is output from the holding portion to the adding and subtracting circuit.

2. The image signal processing apparatus according to claim 1, wherein the counter portion performs counting every horizontal line of the pixels and outputs the already held difference outputs from the holding portion to the adding and subtracting circuit on a horizontal line exceeding the predetermined number of comparison times.

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

an A/D converting portion is included which A/D-converts an output of the adding and subtracting circuit and outputs it to the optical black level determining portion, and

a D/A converting portion is included which is the holding portion and D/A-converts and holds the difference outputs and outputs them to the adding and subtracting circuit.

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

an A/D converting portion is included which A/D-converts the image signals and outputs them to an optical black level determining portion and the adding and subtracting circuit

a register portion is included which is the holding portion and holds the difference outputs as offset values and outputs them to the adding and subtracting circuit.

5. The image signal processing apparatus according to claim 1, wherein the set number of comparison times is set to a value between ⅔

of the total number of optical black outputs on a horizontal line and the total number of the optical black output (both included).

6. The image signal processing apparatus according to claim 1, wherein the image signals are converted into digital signals, compared with the clamp level serving as set digital value, the different outputs serving as digital values are output and the difference output serving as the digital values are compared with a comparison level serving as a set digital value.

7. The image signal processing apparatus according to claim 1, wherein the comparison level has a magnitude between a magnitude equal to that of the random noise of an optical black output signal and a magnitude five times larger than the former magnitude.

8. A camera having the image signal processing apparatus of claim 1 and an optical system for imaging light to be output to the image signal processing apparatus to a solid state image sensor.

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

a step of comparing the optical black outputs from the light shielded pixels with a set clamp level;

a step of outputting differences between the optical black outputs and the set clamp level as difference outputs;

a step of set clamp level clamping image signals in accordance with the difference outputs;

a step of holding the difference outputs;

a step of comparing the difference output of the pixels with a set comparison level every horizontal line of the pixels; and

a step of clamping the image signals by the already-held difference outputs on the horizontal lines when the number of times when the difference outputs are larger than the comparison level exceeds the predetermined number of comparison times.

10. The image signal processing method according to claim 9, wherein the average value of the difference outputs compared with the set clamp level is calculated every the above horizontal line and compared with the set comparison level.

11-15. -15. (canceled)

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

intermediate value outputting means for extracting a median value of signals from the light shielded pixels and outputting it; and

clamping means for adjusting signals from the light shielded pixels to a predetermined level in accordance with a value output from the intermediate value outputting means, wherein

the intermediate value outputting means is provided with first intermediate-value outputting means for dividing signals from the n m (n and m are optional natural numbers) light shielded pixels into sets every n signals and extracting and outputting median values of the sets and second intermediate-value outputting means for forming m output values output from the first intermediate-value outputting means into one set and extracting and outputting median values from the output values

the clamping means adjusts signals from the light shielded pixels to a predetermined level in accordance with a value output from the second intermediate-value outputting means.

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

computing means for calculating and outputting the average value of signals excluding the maximum value and minimum value among signals 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 computing means.

18. An image signal processing apparatus having clamping means for performing clamping for adjusting signals from light shielded pixels of a solid state image sensor having a plurality of effective pixels and the light shielded pixels to a predetermined level, comprising:

averaging means for calculating and outputting the average value of signals from the light shielded pixels and holding the average value of signals from the light shielded pixels used for the last-time clamping; and

comparing means for comparing the average value held by the averaging means with the level of signals from the light shielded pixels;

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 a predetermined threshold value, the average value of signals from the light shielded pixels held by the averaging means and used for the last-time clamping is supplied to the averaging means instead of signals from the light shielded pixels.

19-20. -20. (canceled)