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Burning Software:Archive for February, 2011
Why Is My Video Striped? Scanning Systems and Preview Problems.
When we spoke about HD video, we explained what shorthands for HD videos like 1080p, 1080i and 720p mean.
The letters p and i are used to designate the scanning system: progressive scanning (p) or interlaced scanning (i).
We promised to discuss the scanning systems and related problems later.
So, let’s start.
Scanning systems
A scanning system type characterizes the way the image is being redrawn when refreshing picture.
There are two different scanning systems – progressive scanning and interlaced scanning.
Progressive scanning redraws an image frame (all of its lines) when refreshing each picture.
Interlaced scanning system implies that each frame is divided into two half-frames (or fields). One field contains all the odd lines of the image, the other contains all the even lines of the image. Thus, during the first image refresh operation the system draws odd numbered lines, and then draws the remaining even numbered lines during the second refreshing.
This technique allows to double a frame rate of a video signal without consuming extra bandwidth. Interlaced scanning was initially designed for TV broadcasting so that the refresh rate of a screen fits the power frequency.
Watching an interlaced video on a device that uses progressive scanning method causes a very unpleasant effect.
What is the combing effect? Why does it occur?
Interlace (or combing) effect occurs when an interlaced video is being played on a device that employs progressive scanning. Edges of moving objects have the form of a “comb”, the video is covered by horizontal stripes that distort the image (see Pic. 1).
The cause of this effect is that a progressive scanning combines two adjacent half-frames to draw the image. Lines of these two half-frames interleave, that is the first line from the first half-frame is drawn, then the second line from the second half-frame, the third line from the first half-frame, the fourth line from the second half-frame, and so on. The combined half-frames can contain different motion phases, so that the lines are shifted relative to each other, and the picture looks striped.
Where and when can I see the combing effect?
If you watch TV on your computer using a TV tuner, you have probably seen this effect (as computer monitors use progressive scanning system, while TV broadcasting standards imply interlaced scanning).
Many camcorders also shoot interlaced video, so you will see interlace stripes when watching it on your computer.
At last, you can face this problem when ripping DVD, since many DVDs are interlaced too.
You should remember that the combing artifacts are most visible on moving images.
How to get rid of combing artifacts?
To be played correctly by devices that use progressive scanning, an interlaced video is converted into a non-interlaced form. This process is called deinterlacing. The conversion can be performed both hardwarily (by devices, such as TV sets, DVD players and computer video cards) and softwarily (by the means of video conversion software).
For example, Need4 Video Converter allows applying deinterlacing to MPEG video files. Pic.1 gives an instance of software deinterlacing performed by Need4 Video Converter program.
February 24th, 2011
Posted in Informative | No Comments »
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The problem
Probably each of us has faced the challenge of missing or accidental deletion of files we value.
The most common causes for that can be:
- Accidentally pressing format or delete button on your camera, camcorder, iPod or smartphone;
- Memory card/flash card shows “unformatted/unallocated” drive when you connect it to your computer;
- Sudden disappearance of a file/folder from your iPod, camera, camcorder or smartphone.
The solution
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