What is Interlaced and Progressive?

Interlaced and Progressive are both methods of expressing moving images on the display device. The interlaced method is that each frame is divided into two fields and displayed alternately. The progressive scan method is to display all the images in each frame. The usual scanning method of LCD TV display screen is from left to right and top to bottom, scanning a fixed number of frames per second.

What is Interlaced Scan?

Interlaced scanning means that each frame is divided into two fields. Each field contains all the odd or even scan lines in a frame. Usually, the odd lines are scanned first to get the first field, and then the even lines are scanned to get the second field. Due to the persistence of vision effect, the human eyes will see smooth motion instead of flickering half-frame images. But at this time, there will be flickers that are hardly noticed which makes the eyes easy to fatigue. This kind of flicker is especially easy to notice when the content of the screen is horizontal stripes.

The drawback of interlaced video is that in fast motion, it may be blurred as only half of the image is captured at a time, movement along the frame causes motion artifacts. Particularly when the movement is rapid, causing different positions of the fields. For instance, from a moving car, we can notice motion artifacts if filmed by interlaced. Nowadays, higher power graphics cards have good quality deinterlacing as a built-in feature.

Because the implementation cost is low and the effect is good, it is widely adopted by TV stations as TV broadcast signals, and we are used to watching it. Interlaced scan has ruled for nearly half a century, and this inertia has been extended to the field of computer displays.

What is Progressive Scan?

Progressive scan displays the entire scan frame each time. If the frame rate of progressive scan is the same as the field rate of interlaced scan, the human eyes will see a smoother image than interlaced scan, with less flicker than interlaced scan.

Each frame of image is sequentially scanned line by line by the electron beam. This scanning method is called progressive scanning. Scanning each frame of image through two fields is called interlaced scanning. In these two fields scanning, the first field (odd field) only scans odd lines, scans 1, 3, 5... lines in turn, and the second field (even field) Only scan even rows, scan 2, 4, 6... rows in sequence. In the standard display mode of TV, i means interlaced scanning, and p means progressive scanning.

Compared with interlaced TV, the content of progressive scan TV is clearer. Of course, this refers to progressive in the true sense. If the signal source is still an interlaced signal (such as a TV signal), then a frequency multiplier converter is needed. The actual effect is equivalent to simulating progressively in an interlaced way, parity of the same content copy line, the picture looks dense, but the real details of the picture have not increased. From the point of view of picture quality, this kind of progressive is called false progressive. Therefore, to achieve the best effect with progressive TV, a progressive signal source is required, such as a progressive DVD player, computer display card or digital high-definition signal.

Differences between Interlaced vs Progressive Scan

Interlaced scanning technology plays a great role in the case of insufficient transmission signal bandwidth. The main difference between the display effect of progressive scan and interlaced scan is the stability. The interline flicker of interlaced scan is more obvious. Progressive scan overcomes the shortcomings of interlaced scan, and the picture is smooth and natural without flicker.

Interlaced or Progressive: Which one is Better?

Let’s discuss two instances- two films, one recorded progressively and one recorded interlaced. Now, if the progressive one is played by a traditional broadcasting system which uses interlaced encoding, the system will play them reasonably well. It will not be even noticed that the image is interlaced. But when the interlaced video is played on a screen that uses progressive scanning, problems will arise. Since half the data was not there, the system tries creating progressive images from half ‘stills’ resulting in the missing lines becoming visible. It is evident from here that progressive scan is better than interlaced scan since:

· It provides a more vivid and realistic display, which is appealing.

· With the emergence of modern displays such as LCDs and LEDs, this display technology is permanent.

· Though interlaced scanning is being used in the broadcasting industry till now, continuous technological advancements and falling prices of the associated electronic devices indicate that systems based on progressive scanning will most certainly dethrone those based on interlaced scanning in the near future.

The terms, interlaced and progressive video is the raster scan techniques. The progressive scan is newer technology and interlaced scan is older but widely used. Moreover, making and scanning of progressive scan video is costlier in comparing to interlaced scan however its images and videos qualities are clearer.