Difference between Interlaced and Progressive Scan

Interlaced and progressive scans are raster scanning methods that are both widely employed in analogue video systems. The primary distinction between these scans is that the interlaced scan uses scanning of even and odd marked lines of an image, which are shown sequentially as two separate fields superimposed to display one frame on the screen. In contrast, the progressive scan uses a single sweep over the entire picture at a time.

In this article, you will learn about the difference between an Interlaced and Progressive scan. But before discussing the differences, you must know about Interlaced and progressive scans with their advantages and disadvantages.

What is Interlaced Scanning?

Interlaced scanning is a raster scanning method in which a picture is scanned by dividing a single frame into two fields. These components are known as fields. Each field is called a 2:1 interlace because it comprises half of the lines in the frame. The field interval is the time period between two fields that is equal to half of the frame interval. The two fields are referred to as "top field" and "bottom field" in MPEG specifications. The top field contains the first line and the alternate lines that follow. On the other hand, the bottom field contains the second set of alternate lines.

The main drawback of interlaced scanning is "combing", which reduces video quality. In interlaced videos or images, the combing effect creates zig-zag artefacts. The interlaced scan was popular in the beginning since it used less bandwidth.

Interlaced scanning was popular in the beginning because it uses less bandwidth, which improves temporal resolution and minimizes flickering. Previously, the channels were disseminated via televisions that used data hurled over the airways or coax cable. Interlaced videos save bandwidth by only delivering half of a complete frame at a time, which was useful for boosting refresh rate and providing smoother action on older TV sets.

Advantages and Disadvantages of Interlaced Scan

There are various advantages and disadvantages of an Interlaced scan. Some main advantages and disadvantages of an Interlaced scan are as follows:

Advantages

1. It reduces the cost and complexity of generating and broadcasting content due to bandwidth reduction.
2. The bandwidth demand is reduced by a factor of 2 because just half of the frame is transmitted at a time.
3. It has double the frame rate and refresh rate of progressive scan at a fixed bandwidth.
4. As the interlaced scan is the industry standard, TV manufacturers may develop their OS more easily.

Disadvantages

1. The interline scanning parity cycle results in visible and cleanly arranged line structure lines in the image. The line structure lines become increasingly visible as the screen size increases, affecting the embodiment of image information and the complete picture effect.
2. When viewing a huge light-colored background picture, the field frequency is comparable to the flicker-sensitive frequency of human eyes, and the flicker will be seen.
3. If the item is moving quickly sufficiently to be in other places in the time it brings for both the even and odd lines to be drawn on the screen, an unpleasant motion artefact will appear when viewing very high-speed motion sequences.
4. The parity cycle of interlacing scan causes prominent flicker between scan lines, which is especially noticeable while viewing text.
5. It may purposely introduce blur to correct the motion artefact.

What is Progressive Scan?

Progressive scanning is a scanning method in which a picture is scanned in a single pass successively. It employs an electron beam that constantly scans the image region from top to bottom. It is more effective than interlaced scanning because progressive scanning scans the picture frame by frame. In addition, progressive scanning has no combing effect. As a result, the video generated by progressive scanning is of large quality. As a result, progressive scanning is preferred over interlaced scanning.

The progressive scans may clearly record and display images of fast-moving objects. Another major benefit of progressive scan is that the playing speed of a video is nearly doubles that of the interlaced scan.

Advantages and Disadvantages of Progressive Scan

There are various advantages and disadvantages of the Progressive Scan. Some main advantages and disadvantages of Progressive Scan are as follows:

Advantages

1. The progressive scan uses less bandwidth, which makes it a better option for current HDTVs. As a result, progressive scan has a greater video resolution than interlaced scan.
2. The progressive scan may provide higher-quality images with less noise and distortion by presenting each frame as a whole.
3. It decreases flicker and artefacts because it sends the entire frame at once.
4. Reduced flicker also implies less strain on the eyes after extended use.

Disadvantages

1. It necessitates additional bandwidth, increasing the overall cost and complexity of the system.
2. The interlaced scan is the best way to present live video. It is because progressive scans cannot be "scanned" in real-time.
3. Progressive scan is more vulnerable to visual tearing and other video defects due to the enormous number of frames in a video.

Key differences between Interlaced Scan and Progressive Scan

There are various key differences between the Interlaced Scan and Progressive Scan. Some of the key differences between Interlaced Scan and Progressive Scan are as follows:

1. Interlaced scanning machines divide the entire frame into two parts, with each field having alternate lines that are merged at the time of displaying it. In contrast, progressive scanning machines scan the entire frame at once, from top to bottom.
2. In progressive scans, the speed of presenting a video is nearly double that of the interlaced scan. In contrast, the speed of presenting a video in an interlaced scan is slower than in a progressive scan.
3. Progressive scan is more efficient than interlaced scan because it can collect and display fast-moving objects more clearly. In contrast, the interlaced scan is less efficient than the progressive scan.
4. Interlaced scanning is less popular than progressive scanning. In contrast, Progressive scan is more widely used than interlaced scan.
5. The quality of the progressive scan is strongly supported by the fact that video in 720p (progressive) is smoother than video in 1080i (interlaced). That's why a progressive scan is more preferred for displaying athletic events.

Head-to-head comparison between Interlaced Scan and Progressive Scan

Here, you will learn the head-to-head comparisons between the Interlaced Scan and Progressive Scan. The main differences between Interlaced Scan and Progressive Scan are as follows:

Conclusion

The raster scan methods include interlaced and progressive scans, with progressive being a more recent development and interlaced being an older but still used technique. Progressive video scanning and production are more expensive than interlaced, but the results are sharper. The most important distinction to make here is that progressive scan performs scanning of the whole frame in a single pass. In contrast, an interlaced scan is scanned by splitting a single frame into two fields.