Imaging apparatus

Claim 2

Imaging apparatus comprising means (2) for producing electrical image signals representing the brightness of pixels in a scene; means (6) for controlling the level of said signals; digital means (21,22,23) for detecting pixels in different brightness bands (a to j); and feedback means (22) responsive to said digital means for adjusting said level control means (6); characterised in that said digital means (21,22,23) is operable to determine if there is a difference between the number of said pixels in a high brightness band (a,b,c) and the number thereof in a low brightness band (h,i,j); and feedback means (26) is responsive to said difference for adjusting said level control means (6) at least to reduce said difference.

Claim 3

Apparatus according to claim 1, characterised in that said level control means (6) comprises an analogue DC offset circuit operable to apply an analogue DC offset to the electrical image signals.

Claim 4

Apparatus according to claim 1, characterised in that said high brightness band (h,i,j) is spaced from said low brightness band (a,b,c).

Claim 5

Apparatus according to claim 1, characterised in that said high brightness band is contiguous with said low brightness band.

Claim 6

Apparatus according to claim 1, characterised by gain adjusting means (4); means (22) for determining whether a predetermined proportion of the total number of pixels is within a predetermined intermediate brightness band (b to i or d to g); and further feedback means (22) controlling said gain adjusting means (4) in dependence thereon.

Claim 7

Apparatus according to claim 5, characterised in that said further feedback means (21) is operative to reduce the gain provided by said gain adjusting means (4) if there is less than a first predetermined proportion of the total number of pixels within a first relatively wide intermediate brightness band (b to i) and to increase the gain if there is more than a second predetermined proportion of the total number of pixels within a second relatively narrow intermediate brightness band (d to g).

Claim 8

Apparatus according to claim 6, characterised in that said first predetermined proportion is the same as said second predetermined proportion.

Claim 9

Apparatus according to claim 6, characterised in that said first predetermined proportion is less than said second predetermined proportion.

Claim 10

Apparatus according to any of claims 5 to 8, characterised in that said gain adjusting means (4) comprises an ananalogue gain control circuit.

Claim 11

Apparatus according to any preceding claim, characterised by integration means (12,14) for integrating a plurality of frames.

Claim 12

Apparatus according to claim 10, characterised in that said integration means (12,14) is operable to perform said integration to an increasing extent with increase in gain applied to said image signals.

Claim 13

Apparatus according to claim 11, characterised in that said integration means (12,14) is digital.

Claim 14

Apparatus according to claim 12, characterised in that said integration means (12,14) comprises a frame store (12) for storing data representing pixels in a complete frame.

Claim 15

Apparatus according to any of claim 12, including motion detector means (22) for discontinuing said integration in response to motion in said scene.

Claim 16

Apparatus according to claim 14, including means (22) for adjusting a motion detecting threshold in dependenance upon the gain applied to said image signals.

Claim 17

Imaging apparatus comprising means (21) for producing electrical image signals representing the brightness of pixels in a scene; gain adjusting means (4) for said electrical image signals; digital means (21,22,23) for detecting pixels in different brightness bands (a to i); and feedback means (22) responsive to said digital means (21,22,23) for adjusting said gain adjusting means (4); characterised in that said digital means (22) is operative to determine the number of said pixels in a first relatively wide intermediate brightness band (b to i) and in a second relatively narrow intermediate brightness band (d to g) and said feedback means (22) is operative to reduce the gain if there is less than a first predetermined proportion of the total number of pixels within said first band (b to i) and to increase the gain if there is more than a second predetermined proportion of the total number of pixels in the second band (d to g).

Claim 18

Imaging apparatus comprising means (21) for producing electrical image signals representing the brightness of pixels in a scene; gain adjusting means (4) for said electrical image signals; digital means (21,22,23) for detecting pixels in different brightness bands (a to i); and feedback means (22) responsive to said digital means (21,22,23) for adjusting said gain adjusting means (4); characterised in that said digital means (22) is operative to determine the number of said pixels in a first relatively wide intermediate brightness band (b to i) and in a second relatively narrow intermediate brightness band (d to g) and said feedback means (22) is operative to reduce the gain if there is less than a first predetermined proportion of the total number of pixels within said first band (b to i) and to increase the gain if there is more than a second predetermined proportion of the total number of pixels in the second band (d to g).

Claim 19

Imaging apparatus comprising: means (2) for producing electrical image signals representing the brightness of pixels in a scene, said signals being produced in a succession of frames; and gain adjusting means (4) for adjusting the gain applied to said electrical image signals; characterised by digital integration means (12,14) operable to integrate said image signals over a plurality of frames by adding the signals representing corresponding pixels in each frame of said plurality; and means (22) for increasing and decreasing the number of frames in said plurality with increase and decrease of said gain.

Claim 20

Imaging apparatus comprising: means (2) for producing electrical image signals representing the brightness of pixels in a scene, said signals being produced in a succession of frames; and gain adjusting means (4) for adjusting the gain applied to said electrical image signals; characterised by digital integration means (12,14) operable to integrate said image signals over a plurality of frames by adding the signals representing corresponding pixels in each frame of said plurality; and means (22) for increasing and decreasing the number of frames in said plurality with increase and decrease of said gain.

Claim 21

Imaging apparatus comprising means for producing electrical image signals representing the brightness of pixels in a scene; digital means (21,22,23) for calculating the proportion of the total number of pixels in the scene within an intermediate brightness band and to compare said calculated proportion with a predetermined proportion; and feedback means (22) for reducing or increasing gain applied to said electrical image signals according to whether said calculated proportion is less or more than said predetermined proportion.

Claim 22

Imaging apparatus comprising means for producing electrical image signals representing the brightness of pixels in a scene; digital means (21,22,23) for calculating the proportion of the total number of pixels in the scene within an intermediate brightness band and to compare said calculated proportion with a predetermined proportion; and feedback means (22) for reducing or increasing gain applied to said electrical image signals according to whether said calculated proportion is less or more than said predetermined proportion.