how are pictures and video converted to electric signals?

Answer 1

Divide the question.
Pictures are converted to electric signals by scanning the picture. Each spot on the picture is examined and the light being reflected is divided by filters to 3 sensors which produce Red-Blue-Green (usually) info. This info is digitized and passed on in some organized manner which the receiver or reader has to understand. Some methods encode the details of every spot and make very big files. Others (such and .gif or .jpg) compress the size by reporting that (for example) "22 dots of green follow" which can be done in about 3 bytes instead of 66.
Since video in normally picked up by either scanning with an electron beam or picking up the bits off a CCD chip, and there are fewer standards for video transmission, the same process goes on, except that for each video format there is an exact number of spots (pixels) per row and an exact number of rows per image.

Answer 2

The picture make an image on a mask from we get analog signal, which is then converted into digital signal

Answer 3

The audio of the video is converted through the microphone.
The pictures are converted in different methods:
any color can be splited to Red, Green and Blue, so each point on the picture can be represented as RGB in analog systems the high of the pulse can present a color or each color in RGB can be presented as a different pulse. in digital systems each color is set as of binary sequence.

Answer 4

An ADC (Analogue to Digital Converter) does that. It converts the analogue, or real world representation of pictures, videos to digital representation. These digital symbols are nothing but electric pulses inside the computer system.