Method and system in digital imaging for adjusting exposure and a corresponding device

• US 20070009253A1
• Filed: 06/14/2004
• Published: 01/11/2007
• Est. Priority Date: 06/30/2003
• Status: Active Grant

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Nikkanen, Jarno, Kalevo, Ossi
• Granted Patent: US 7,474,847 B2
• Time in Patent Office: Days
• US Class Current: 396/234
• CPC Class Codes: G03B 7/097 for control of both exposure time and aperture
• CPC Class Codes: H04N 23/71 Circuitry for evaluating the brightness variation

Abstract

The invention relates to a method in digital imaging for adjusting exposure, in which one or more exposure parameters (ET, AG) of a camera device are adjusted in connection with imaging. In the method, a histogram formed from a raw image frame (12) is analysed, from which one or more special values (R_high, R_low) are specified and which compared with a target level (H_tgt, L_tgt) set for them, and, if a special value (R_high, R_low) differs from the target level (H_tgt, L_tgt), the exposure parameters (ET, AG) are adjusted to achieve the target level (H_tgt, L_tgt).

Claims

1. A method in digital imaging for adjusting exposure, in which one or more exposure parameters of a camera device are adjusted in connection with the imaging and in which method

(i) a raw image frame corresponding to exposure parameters is captured from a camera sensor,

(ii) a histogram is formed from the raw image frame,

(iii) at least one characteristic value, for example, a mean value W specified in a set manner, is specified from the histogram,

(iv) the characteristic value is compared with a target level set for it,

(v) if the said characteristic value differs from the target level set for it according to a set criterion, the exposure parameters are adjusted in order to reach the target level and/or,

(vi) a return is made to stage,

characterized in that, in the method, in stage, in addition to the possibly specified mean value, one or more special values, specified in a set manner, are specified from the histogram as the said characteristic values, for which a target level, specified in a set manner, is also set, and in which for at least one characteristic value a such an offset is also specified, corrected by means of which the characteristic value, is guided towards the target level set for it, and as a result of the guiding of which one or more of the other characteristic values are guided towards the target levels set for it, and on the basis of the characteristic values and of the offsets specified for them, the said exposure parameters are then adjusted.

2. A method according to claim 1, characterized in that preferably upper and lower limits are set in the histogram for the target levels which specify the target interval for the target levels.

3. A method according to claim 1, characterized in that the target intervals are specified according to the dynamic characteristics of the camera sensor.

4. A method according to any of claim 1, characterized in that the said special values of the histogram, specified from the raw image frame are specified according to its pixel portions/distribution.

5. A method according to any of claim 1, characterized in that, in the method

a first offset is specified for the first special value, by means of which it is guided to the target interval set for it,

the mean value is estimated, which follows from the said guiding, and is compared with the target interval set for it,

if the estimated mean value is not guided to the target interval a second offset, such that the mean value is guided to the target interval set for it, is specified additionally for the first special value,

the exposure parameters are specified on the basis of the said special value and the offsets specified for it.

6. A method according to claim 1, characterized in that, in addition, prior to the adjustment of the exposure parameters

an examination is made as to whether the saturation condition set as a result of the guiding made for the said first special value is met and

if it is met, then a such an offset OFF3′

is specified for the said second special value, by means of which

the second special value is guided to the target interval set for it and which

offset OFF3′

meets the saturations criteria set for the target interval, and after which

the said exposure parameters are specified on the basis of the second special value and of the offset specified for it.

7. A method according to claim 6, characterized in that, in addition, prior to the adjustment of the exposure parameters

an examination is made as to whether the saturation condition set as a result of the guiding of the said first special value is met and

if the condition is not met, a such an offset, by means of which it is guided to upper limit of the target interval set for it is specified for the first special value, and after which

the said exposure parameters are specified on the basis of the first special value and of the offset specified for it.

8. A method according to claim 1, characterized in that, when the histogram is formed from the raw image frame, only part of the data is recorded, such as, for example, 1/10- 9/10, preferably ⅛

.

9. A method according to claim 8, characterized in that the brightness value of the brightest pixel from a set manner selected pixel neighbourhoods is recorded from the raw image frame into the histogram.

10. A method according to claim 1, characterized in that the said first special value is specified in such a way that 95-99.9% of the pixels of the histogram have a brightness value that is preferably darker than the special value.

11. A method according to claim 1, characterized in that the target levels and the target intervals are set dynamically.

12. A method according to claim 11, characterized in that the target levels and the target intervals of the special values are modified according to the ambient light level.

13. A method according to claim 12, characterized in that the ambient light level is estimated on the basis of the previous exposure parameters.

14. A system in a digital imaging chain, in which the system includes a camera sensor and modular portions arranged in connection with it for processing the image data and in which, in connection with the camera sensor, there is a portion adjusting the exposure parameters, and which system is arranged to

(i) capture a raw image frame corresponding to exposure parameters from the camera sensor,

(ii) form a histogram from the raw image frame,

(iii) specify at least one characteristic value, for example, a mean value specified in a set manner, from the histogram,

(iv) compare the characteristic value with a target level set for it,

(v) if the said characteristic value differs from the target level set for it according to a set criterion, adjust the exposure parameters in order to reach the target level and/or,

(vi) continue from stage (i),

characterized in that, in addition to the possibly specified mean value, there are arranged to be specified from the histogram, as the said characteristic values, one or more special values, specified in a set manner, for which a target level, specified in a set manner, is also arranged to be set, and in which, for at least one characteristic value a such an offset is arranged to be defined, corrected by which the characteristic value is arranged to be guided towards the target level set for it and as a result of which guiding one or more of the other characteristic values is/are arranged to be guided towards the target values set for it, and, on the basis of the characteristic values of which and of the offsets specified for them the said exposure parameters are then arranged to be adjusted.

15. A digital imaging device, which comprises a camera sensor and modular portions arranged in connection with it for processing the image data and in which, in connection with the camera sensor, there is a portion adjusting the exposure parameters, and which imaging device is arranged to

(i) capture a raw image frame corresponding to exposure parameters from the camera sensor,

(ii) form a histogram from the raw image frame,

(iii) specify at least one characteristic value, for example, a mean value specified in a set manner, from the histogram,

(iv) compare the characteristic value with a target level set for it,

(v) if the said characteristic value differs from the target level set for it according to a set criterion, adjust the exposure parameters in order to reach the target level and/or,

(vi) continue from stage (i),

characterized in that, in addition to the possibly specified mean value, there are arranged to be specified from the histogram, as the said characteristic values, one or more special values, specified in a set manner, for which a target level, specified in a set manner, is also arranged to be set, and in which, for at least one characteristic value a such an offset is arranged to be defined, corrected by which the characteristic value is arranged to be guided towards the target level set for it and as a result of which guiding one or more of the other characteristic values is/are arranged to be guided towards the target values set for it, and, on the basis of the characteristic values of which and of the offsets specified for them the said exposure parameters are then arranged to be adjusted.