Circuit arrangement for indicating ambient light conditions of a video pickup and video display device

Users of video telephones or multimedia terminals cannot determine whether ambient light conditions during a transmission to another terminal are always of good quality. Provision is made for an indication regarding the ambient light conditions during a telephone call, and control thereof. By means of a circuit arrangement including a photocell (F) to detect incident light, a signal (II) is formed, which corresponds to the ambient light conditions. The signal (II) is displayed together with a video signal (I), or is used for control purposes.

TECHNICAL FIELD 
The invention concerns a circuit arrangement for indicating the ambient 
light conditions of a video pickup and video display device. The invention 
further concerns a circuit arrangement for controlling the ambient light 
conditions of a video pickup and a video display device. 
BACKGROUND OF THE INVENTION 
For example, video telephones that contain a self-image control, as well as 
the possibility of adjusting color, brightness and contrast, are known 
from the state of the art. The color, brightness and contrast adjusting 
possibilities serve to control the video received by another user. In 
addition, these video telephones offer a so-called picture-in-picture 
function. To understand the function of the self-image control it must be 
understood that the self-image is displayed at the start of a telephone 
call. The quality of the self-transmitted image can be controlled at the 
start of the telephone call, but only as to whether the transmitted 
picture window is well placed, or whether e.g. only a partial area is 
being transmitted. (Video Telephone XITEL "Many a sight becomes the most 
cherished moment"; from: Prospect; in: Telecom; February 1994). 
SUMMARY OF THE INVENTION 
It is the task of the invention to provide a circuit arrangement that 
enables the user of a video pickup and video display device to determine 
at any time whether the quality of the image he is transmitting to another 
video pickup and video display device is of good quality, for its possible 
correction. 
This is accomplished by a circuit arrangement for indicating ambient light 
conditions of a first video pickup and video display device, comprising at 
least one photocell having an electric output corresponding to incident 
light, an amplifier circuit, connected thereto for generating a signal 
proportional to the incident light, and a means which receives a video 
signal from a second video pickup and video display device and mixes said 
video signal with the proportional signal, the mixed signal being fed to 
the first video display device, which reproduces the video signal and 
provides an indication of the signal proportional to the incident light. 
It is further accomplished by circuit arrangement for controlling a first 
video pickup and video display device in accordance with ambient light 
conditions, comprising at least one photocell having an electric output 
corresponding to incident light, an amplifier circuit connected thereto 
for generating a signal proportional to the incident light, and a gain 
controller which receives the proportional signal, is connected to the 
first video pickup device, and controls the first video pickup device in 
accordance with the ambient light conditions. 
Advantages of the invention are that a high video quality can be attained 
at any time by the receiving user of a video pickup and video display 
device, and does not depend on the purely subjective impression of a user. 
This high video quality does not depend on the room conditions and the 
time of day during which a transmission takes place. Another advantage is 
that the image received from another video pickup and video display device 
does not require fading down in order to perform a new self-image control, 
or to derive the video quality from a much smaller image with 
picture-in-picture technology.

BEST MODE FOR CARRYING OUT THE INVENTION 
The following explains in detail a circuit arrangement for indicating 
ambient light conditions by means of a configuration example and FIG. 1. 
A circuit arrangement UA of a first video pickup and video display device 
M1, C1 for indicating ambient light conditions, comprises at least one 
photocell F. This photocell F serves to detect incident light. The 
photocell F is connected to an amplifier circuit V. This amplifier circuit 
V generates a signal II which is proportional to the incident light. This 
signal II is sent to a means A. This means A also receives a video signal 
I transmitted by a second video pickup and video display device M2, C2. 
The transmitted video signal I is mixed with the proportional signal II in 
the means A. 
The thus mixed signal III is transmitted to the video display device M1 for 
display. The video signal is reproduced in this video display device M1 
and the signal which is proportional to the incident light is indicated. 
The form of the indication can be selected as an analog display or a 
digital display. Another possibility is to provide a bar-chart display. 
The subject of the indication is directly proportional to the illumination 
level. 
The photocell F, which detects incident light, is preferably installed in 
the direction of the video pickup device C1. A possible video pickup 
device C1 is a commercial camera for example, or a camera such as is used 
for video telephony. A possible video display device M1 is a monitor for 
example, such as is known for video telephony or for multimedia terminals. 
The video signal detected by the video pickup device C1, therefore the 
camera, is transmitted to the second video pickup and video display device 
M2, C2 via a gain controller VR. This takes place e.g. by using a 
telecommunications network, e.g. a broad-band network. 
Another possible indication is for the means A to evaluate the signal II 
which is proportional to the incident light by means of threshold 
evaluation, so that the indication on the video display device M1 shows 
directly whether or not the ambient light conditions are sufficient. This 
can be configured to visually indicate a difference between too dark and 
too light. 
In the following, a further configuration example is explained in more 
detail by means of FIG. 2. 
A circuit arrangement UA for adjusting ambient light conditions in a first 
video pickup and video display device M1, C1 comprises at least one 
photocell F. The photocell F serves to detect incident light. This 
incident light is preferably detected in the direction of the video pickup 
device C1. An example of a video pickup device C1 is a commercial camera 
for instance, and an example of a video display device M1 is a monitor of 
a video telephone or a multimedia device. The photocell F is connected to 
an amplifier circuit V. The amplifier circuit V generates a signal II 
which is proportional to the incident light. The proportional signal II is 
sent to a gain controller VR. The gain controller VR is directly connected 
to a first picture by a first video pickup device C1. For example, a 
threshold evaluation takes place in the gain controller VR, which 
indicates whether the ambient light conditions are satisfactory or 
unsatisfactory. In case the ambient light conditions are unsatisfactory, a 
direct adjustment of the first video pickup device takes place. 
In a further example, the signal II can be directly applied to the video 
pickup device C1 (this is shown by the dotted line in FIG. 2). Video 
signals coming from the second video pickup and video display device M2, 
C2 are sent to a means A, which is directly connected to the video display 
device M1. In this way, video signals coming from the second video pickup 
and video display device M2, C2 are displayed on the monitor. 
A special form of a video pickup and video display device is e.g. a monitor 
with a semitransparent mirror, behind which a camera is located. A special 
advantage of this integrated solution is to locate at least one photocell 
F behind the semitransparent mirror. This in particular is advantageous, 
because a part of the illumination level, or the ambient illumination 
level, is absorbed by the semitransparent mirror. 
A further advantageous configuration is to arrange several photocells F to 
cover the entire image field of the camera. This is particularly necessary 
when a large image field must be covered. To that effect, a number of 
photocells F are distributed over a certain area. The amplifier circuit V, 
which is connected to the number of photocells, forms the signal II by 
averaging the values of the light detected by the photocells. 
The circuit arrangements presented herein find special application in the 
indication and control of video telephones, or multimedia terminals as 
well. In the office or in the home, video telephones and multimedia 
terminals, which are relatively large in size, are located in a fixed 
place. If the ambient light conditions change, e.g. due to clouds in the 
environment during a telephone call, these circuit arrangements are able 
to indicate or control this to ensure that a high quality video is 
transmitted at any time.