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Difference Between Interlaced and Progressive Scan
Both interlaced and progressive scan are types of raster scanning techniques extensively used in analog video systems. The basic difference between interlaced scan and progressive scan is that the interlaced scan employs the scanning of even and odd marked lines of a picture which are displayed consecutively as two isolated fields that are superimposed to show one frame on the screen, while the progressive scan employs a single sweep over the whole picture at a time.
In this article, we will discuss the important differences between interlaced and progressive scan. Let's start with some basics of interlaced scan and progressive scan individually.
What is Interlaced Scan?
Interlaced scanning is a raster scanning technique in which the scanning of a picture is performed by partitioning a single frame into two parts. These parts are termed as fields. Each field consists of half of the lines exists in the frame, and is called as 2:1 interlace. The time interval between two fields which is equal to half of the frame interval is known as field interval. As per the MPEG standards, the two fields are called "top field" and "bottom field". The top field is one that includes the first line and the following alternate lines, whereas the bottom field is one that has the second set of alternate lines.
The major disadvantage of interlaced scanning is "combing" which degrades the video quality. The combing effect produces zig-zag artifacts in the interlaced video or image. Interlaced scan was used in the early days, as it required less bandwidth.
What is Progressive Scan?
Progressive scanning is a scanning technique in which the scanning of a picture is performed in single pass sequentially. The working mechanism of the progressive scan uses an electron beam that continuously scans the image area from top to bottom. Progressive scanning is relatively more efficient than interlaced scanning, as it scans the image frame by frame. Also, there is no combing effect present in case of progressive scanning. Therefore, the video produced by progressive scanning is of high quality. For this reason, progressive scanning is promoted more over interlaced scanning.
Progressive scan has the ability to capture and show the image of fast moving objects clearly. Another important advantage of progressive scan is that the speed of playing a video is faster which is approximately double of that in the case of interlaced scan.
Difference between Interlaced Scan and Progressive Scan
The following table highlights the important differences between interlaced scan and progressive scan −
| Interlaced Scan | Progressive Scan |
|---|---|
| In interlaced scan, the scanning takes place by dividing one frame. | In progressive scan, scanning takes place frame by frame. |
| It is less efficient in comparison to progressive scan. | It is more efficient in comparison to interlaced scan. |
| The displaying video speed is less in comparison to progressive scan. | The video being displayed is quicker in comparison to interlaced scan. |
| It shows combing effect. | No combing effect is present in progressive scan. |
| The video quality is not great. | The video quality is better in progressive scan. |
| It is not promoted as much as progressive scan. | It is promoted more in comparison to interlaced scan. |
Conclusion
The most significant difference that you should note here is that interlaced scan performs scanning of a frame by dividing it into two fields, whereas progressive scan performs scanning of the whole frame in a single pass.
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