What is Frame Size?

Updated: Oct 25, 2019

Today, I am going to talk about Frame Size, following Frame Rate. In "What is frame rate?", Frame defined as one still image. A word Size combined with Frame, so you can see that the word "Size" means the size of the video screen.

It commonly marks to as Horizontal pixels x Vertical pixels, also called to as Resolution. This term refers to how many pixels on the horizontal and vertical axis of the screen. And frame size classified as Analog and Digital depending on the TV scanning method. I will talk more in detail below.


#01. Analog

First, in the analog, it used the scanning method that arranges horizontal lines to vertically, and it is called either Height or Vertical standard; it generally expressed as 480P, 720P, 1080P or 480i, 720i, 1080i. These numbers represent the number of pixels on the vertical axis. In other words, 480P means a display has 480 pixels on the vertical axis.

#02. Digital

During the transition from analog to digital age became not significant for scanning methods because High-resolution standards such as 2K, 4K, and 8K, that based on either width or horizontal axis, are used. These numbers represent the numbers of pixels on the horizontal axis of a display. Like the above, 2K means the screen has about 2,000 pixels on the horizontal axis.


What is the Picture Element (PEL)?

Of course, as changes to the age of digital, there are new ways of presenting the resolution with certain standards, such as SD, HD, Full HD (FHD), and Ultra HD (UHD). In general, 480P referred to as SD, 720P as HD, 1080P as FHD, and 2K or above as UHD. Let’s talk about pixels little bit further, and I mentioned above that the display size is expressed with Number of pixels on the horizontal axis x Number of the vertical axis. Where "x" is a multiplication sign, not a simple notation.

For example, 1080P constitutes 1920 pixels on the horizontal axis, and 1080 pixels on the vertical axis and the multiplication of these two values ​​is the resolution. In other words, 1080P is calculated as 2,073,600 which is about 2 million pixels. So the 2 million pixels are called FHD.


Why is Frame Size based on the scanning method?

You need to know about Scanning to have a better understanding of how frame size is defined. Scanning is basically How to draw a screen? when displaying on a TV or a monitor. In other words, it is a method of creating a screen, and there are analog scanning and digital scanning. I focus on analog scanning.


For the analog scanning, it marked with "P" or "i." The P represents the Progressive scanning in which all the row draw vertically in sequential order, and the i represents the Interlaced scanning in which it describes the odd-numbered rows first, and the even-numbered rows later.


#01. Field

Since the interlaced scanning not commonly used recently, we are more used to the progressive notation such as 720P and 1080P. The interlaced scanning is a method commonly used in the past when image transmission technologies not developed, and when the vertical length is 1080 pixels, it creates 1080 vertical rows based on these pixels. These vertical rows are called Field.


#02. Scanning

As mentioned before, the progressive scanning is to fill out this field from up to bottom in sequential order while the interlaced scanning is to fill out this field by one-half of rows first and the other half in the next. At this time, the field is drawn from left to right at breakneck speed regardless of a scanning method. It is called Left-field, and the opposite is called Right-field.


Therefore, in the past TV broadcasting system, it was essential to indicate whether the image transmits from the station is P/i, and Left/Right. But now we are in the more advanced digital age. So I think this information or history is not so important, so you just need to understand that "Oh, people used these methods in the past!"



Today, I have selected about this topic to explain the scanning method of the progressive and the interlaced as I promised last time. So I hope this post helps.


Thank you!


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