NTSC, PAL, vs SECAM
During the early days of TV, a number of standards came about that governs how the information is to be transmitted from the studio, to the homes of the viewers. Three eventually came out; NTSC, PAL, and SECAM. There are a number of differences between NTSC, PAL, and SECAM. Let’s start off with the refresh rates. NTSC uses a refresh rate of 60Hz while PAL and SECAM both use a refresh rate of 50Hz. The refresh rate is the number of times the image on the screen changes to simulate the illusion of motion. NTSC thus has more fluid motion because of the 10 more frames per second.
Consequently, NTSC only uses 525 with only 486 of them visible. The rest are used as control mechanisms for synchronization and vertical retrace. PAL and SECAM both have a higher resolution by using 100 more lines per frame. Out of the 625 lines of PAL and SECAM, 576 are visible and the rest are used for control as well.
The biggest drawback of NTSC is its inability to correct the colors on-screen automatically. Thus, it needs a tint control that a user needs to adjust manually. Seeing the problem, the makers of PAL and SECAM used phase reversal in order to automatically correct the color and eliminate the need for a tint control.
It is not only PAL and SECAM that has similarities because PAL simply tried to improve on NTSC while SECAM changed some of the approaches used by NTSC; one of these is the use of QAM. QAM stands for Quadrature Amplitude Modulation and it is the technique that is used both by NTSC and PAL in modulating the chrominance. SECAM didn’t use QAM, opting instead to use Frequency Modulation or FM. This gives SECAM superior signal over longer distances but increased crosstalk between the luminance and chrominance.
Another area where SECAM is different from both PAL and NTSC is in the transmission of blue and red. With NTSC and PAL, both the blue and red are broadcast concurrently. With SECAM, they are sent alternately. The alternate manner of sending colors in SECAM eliminates the color artifacts that are present in NTSC and PAL but halves the color resolution.
Summary:
1.NTSC uses a refresh rate of 60Hz while PAL and SECAM use 50Hz
2.NTSC has 525 lines while PAL and SECAM use 625 lines
3.NTSC requires a tint control while PAL and SECAM doesn’t
4.NTSC and PAL use QAM while SECAM uses FM
5.NTSC and PAL sends the red and blue colors together while SECAM sends them alternately