Component Video, Y / C, Composite and RGB SIGNAL
Returning to the previous article we review the process of capturing the video signal.
The study's primary image capture device that we have, the human eye, is derived from technology used in man-made artifacts to take pictures. These devices, cameras, acting in the image of the human eye. At least to some extent.
We will not go to detail the process by which you can capture and focus light through optical images, as does the human eye, but they point out, roughly, how it behaves to different wavelengths that make up " color "image.
. Photoreceptor cells that are in the eye are sensitive to different wavelengths of the electromagnetic spectrum. y ultra- violetas , no son visibles por el ojo humano. Only collect the spectrum of visible radiation, obviously belonging to the colors of the rainbow, being outside, the radiation that are beyond the colors located at the margins of that rainbow, ie, infra-red and ultra-violet are not visible to the human eye.
These photoreceptor cells called rods and cones, the cones being primarily responsible for color perception. According to studies, there would be three types of cones, each sensitive to different wave logitud, namely the corresponding to the colors red (red), GREEN (green) and BLUE (blue).
That is, the eye would be an RGB device that is capable of reproducing all the basic colors of additive combinanión these three unique colors.
Now we will see whence comes the selection of these three colors as a basis for capturing images, but as we know, at first the television technology was only able to reproduce black and white images, ie luminance only collected. Gradually it developed the technology to reproduce also the color, but it was essential to make it compatible with the previous black and white TV.
Thus, the luminance signal and record the black and white TV was joined by the chrominance signal, thereby providing color information. This is the basis of the first type of video signal that we will discuss: the signal COMPONENTS.
SIGNAL COMPONENTS
Pick up the luma and chroma separately. This was done to make it compatible with the receivers of black and white TV at the time. Use the RGB tristimulus model of the human eye.
This signal is often represented as YUV, but the correct way to represent it is Y 'CBCR. es su traducción digital que es la que nos ocupa en este caso) When analog is called YPbPr (Y 'is its translation CBCR digital is at hand in this case)
Y '= represents the luma, the grayscale image. It uses the wavelength corresponding to green to form this signal. Color was chosen because the human eye's photoreceptor cells are more sensitive to such radiation. The apostrophe (') reminds us that this signal is not linear but logarithmic, which requires gamma correction (a complex issue to be discussed in later articles.
CBCR = represents the chrominance (C), the color information. The colors red (R) and blue (B) are removed mathematically (BY, RY) and ride in the signal, apart and separate from the luminance. Although a way to compress the RGB wavelengths, is a high quality signal used at the professional level.
From here, they developed other signs of inferior quality, but also efficient domestic players or electronic devices cheaper. Are the signs of S-VIDEO and composite signals.
S-VIDEO SIGNAL OY / C
COMPOSITE-COMPOSITE VIDEO SIGNAL
At this signal, characteristic of almost all home video devices, the lumancia and chroma are multiplexed together. Together but are modulated at different frequencies, so the quality is much lower than the previous ones, due to interference between the signals and the loss involved include the three components in the same bandwidth.
Apart from these three video signals there is a third type that is considered superior to them all. This is pure RGB signal.
RGB
As we have seen the beginning of this article, the eye is an RGB device, therefore, a signal that mimics their behavior may more reliably reproduce the colors and their Corresponding luminance value. This signal exists, but it is commonly used to capture video, but to reproduce colors in computer systems. It is the type of signal used computer monitors, projectors and is generally reproduces color as the graphics card of your computer.
) de manera qu In Europe, the RGB signal is implemented in the SCART connector (SCART famous) so qu
and it is often found in computer outside the home players and most of the TVs, while in countries outside the European Union is not commonly used, replacing the signal for Y / C.
In the RGB system, there is no need to add a luma signal as grayscale and black and white pure form with the combination of all three colors equally.
CAPTURING THE VIDEO SIGNAL
When we start working to identify the various signals to give our camera or VTR as well as the entries we have in our video capture. We always select the best quality, presumably because our camera will record the signal at least in that format.
Apart from the analog jacks we have seen, they can go on different types of digital interfaces such as FireWire, SDI, HDMI, DVI ... that discussed in detail in later articles.
We must analyze what the video signal is the best and what is the correct interface will to introduce a signal loss on our editing system.
