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1080i HD - is it converted to 25 or 50 frames p/s? |
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#26 |
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no, it gives you 50 fields per second.
A crt dipslays the fields alternatively. It's just downscaled to 625. |
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#27 |
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Without any electronic jiggery pokery 1080i gives you 25fps from UK Digital transmissions just as 576i does.
average frame rate achieved=50 If I play back an iplayer HD clip (downloaded with get_iplayer before this was blocked), I get average frame rate achieved=25 |
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#28 |
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A field is transmitted in 1/50 sec, two combined make a single 1/25 sec frame.
A crt scans odd and even lines in 1/50 sec for each alternate field. Persistance of the screen phosphors build the appearance of a single frame. It's downscaled to 720 x 576 the same format as a uhf analogue TV picture PAL at 25fps. On a crt The fields are displayed sequentially and convey the motion between them. As yousay it's only the "appearance" of a single frame. |
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#29 |
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They are not combined into a frame on a crt as your explanation (and mine in the previous post) describes.
The fields are displayed sequentially and convey themotion between them. Read up how it really works http://en.wikipedia.org/wiki/PAL A progressive display simply scans line 1 then 2 then 3 etc but there are very few crt TV's that can display a progressive signal and those that can require a component input. |
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#30 |
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Quote:
Absolute rubbish
1 field every 1/50 sec != 1 full frame every 1/25 sec. |
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#31 |
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erm no, I'm saying the deinterlacing techniques used in modern TVs doesn't reduce the picture to 25 fps. If it did you lose the temporal resolution of 50i video sources.
That's why the small (IMO) reduction in spatial resolution of 720p makes it better than 1080i, it can transmit a genuine 50 frames a second. Full resolution, spatial (at 720) and temporal (at 50): no compromises (if you are happy with the jump from 576 to 720).. |
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#32 |
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Absolute rubbish, a crt has two scanning coils one generates the horizontal raster with a left to right scan and a rapid flyback to scan the next line which is the next but one using the vertical scan coils. After the complete field is scanned to the screen the vertical scan flybacks to to line 2 and fills in the blanks in the same way. In the PAL system each alternate line scanned is reversed in phase (PAL is phase alternate line). No CRT of any age can generate 50 frames/second
Read up how it really works http://en.wikipedia.org/wiki/PAL A progressive display simply scans line 1 then 2 then 3 etc but there are very few crt TV's that can display a progressive signal and those that can require a component input. Since there are two fields in every frame, a television (CRT) actually updates the display at 60 fields per second (or 50 fields per second for PAL/SECAM video). Each field is displayed 1/60th of a second after the preceding field (or 1/50th of a second for PAL/SECAM video). " |
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#33 |
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It does and you do (or you lose spatial resolution).
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#34 |
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LCD and Plasma build up the image in memeory (from whatever source) and then 'blast' the picture to the screen effectively in a single action, it's not built up progressively, and there's no reason (or advantage) to do so.
You actually think a Full HD LCD display has 6,220,800 separate wires to the display along with circuitry that is capable of altering the voltage on every one of those wires instantaneously |
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#35 |
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Each field is displayed 1/60th of a second after the preceding field (or 1/50th of a second for PAL/SECAM video). [/b] "[/i]
The persistance of the phosphur on a CRT is designed specifically for the correct decay period to achieve this. LCD/Plasma duplicate it by combining both fields in a single frame and displaying them as one frame. |
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#36 |
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[quote=d'@ve;41168168]It does and you do (or you lose spatial resolution).
QUOTE] It depends on how the deinterlacing is performed. |
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#37 |
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Here's a full analysis of a BBC-HD 1080i transmission
General ID : 802 Complete name : E:\BBC HD Preview_20100501_1403.ts Format : BDAV Format/Info : BluRay Video File size : 69.7 MiB Duration : 54s 512ms Overall bit rate : 10.7 Mbps Video ID : 5500 (0x157C) Menu ID : 6940 (0x1B1C) Format : AVC Format/Info : Advanced Video Codec Format profile : High@L4.0 Format settings, CABAC : Yes Format settings, ReFrames : 4 frames Duration : 54s 512ms Bit rate : 9 643 Kbps Width : 1 440 pixels Height : 1 080 pixels Display aspect ratio : 16/9 Frame rate : 25.000 fps Resolution : 24 bits Colorimetry : 4:2:0 Scan type : Interlaced Scan order : Top Field First Bits/(Pixel*Frame) : 0.248 Stream size : 62.7 MiB (90%) Audio #1 ID : 5501 (0x157D) Menu ID : 6940 (0x1B1C) Format : AC-3 Format/Info : Audio Coding 3 Duration : 54s 528ms Bit rate mode : Constant Bit rate : 384 Kbps Channel(s) : 6 channels Channel positions : Front: L C R, Surround: L R, LFE Sampling rate : 48.0 KHz Video delay : -1s 129ms Stream size : 2.50 MiB (4%) Language : English Audio #2 ID : 5502 (0x157E) Menu ID : 6940 (0x1B1C) Format : MPEG Audio Format version : Version 1 Format profile : Layer 2 Duration : 54s 480ms Bit rate mode : Constant Bit rate : 256 Kbps Channel(s) : 2 channels Sampling rate : 48.0 KHz Resolution : 16 bits Video delay : -1s 49ms Stream size : 1.66 MiB (2%) Language : nar Text ID : 5504 (0x1580) Menu ID : 6940 (0x1B1C) Format : DVB Subtitles Language : English Menu ID : 258 (0x102) Menu ID : 6940 (0x1B1C) Format : AVC / AC-3 / MPEG Audio / DVB Subtitles List : 5500 (0x157C) (AVC) / 5501 (0x157D) (AC-3, eng) / 5502 (0x157E) (MPEG Audio, NAR) / 5504 (0x1580) (DVB Subtitles, eng) Language : / eng / NAR / eng |
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#38 |
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Quote:
Quote:
It does and you do (or you lose spatial resolution).
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#39 |
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To be more accurate, the second field is displayed while the previous one is still showing - giving 25 frames per second from the 50 fields.
The persistance of the phosphur on a CRT is designed specifically for the correct decay period to achieve this. LCD/Plasma duplicate it by combining both fields in a single frame and displaying them as one frame. OK, so if the fields are displayed at the same time why is interlaced always used for sport due to it's better motion portrayal? If you combine (weave) two interlaced fields together and display them as one progressive frame at the same time on a plasma/lcd, you lose the temporal resolution advantage of 50i. I can assure you the tenns or the football I am watching does not have the motion judder of a 25psf drama or film source. |
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#40 |
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I can assure you the tenns or the football I am watching does not have the judder motion of a 25psf drama.
And don't forget, you can only compare motion judder on live sports with UK drama recorded at 25 fps - US drama recorded at 30 fps will usually have dreadful judder when converted for UK TV. |
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#41 |
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LOL, thanks for the laugh, I've not seen a post quite as comical as that for quite a while on these boards.
You actually think a Full HD LCD display has 6,220,800 separate wires to the display along with circuitry that is capable of altering the voltage on every one of those wires instantaneously Now who's laughing |
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#42 |
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Here's a full analysis of a BBC-HD 1080i transmission
Width : 1 440 pixels Height : 1 080 pixels Display aspect ratio : 16/9 Frame rate : 25.000 fps |
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#43 |
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"In the second type of recorded video, called interlaced video, each field represents a unique instance in time. More specifically, each field of video represents a point in time 1/60th (1/50th) of a second later than the preceding field."
OK, so if the fields are displayed at the same time why is interlaced always used for sport due to it's better motion portrayal? If you combine (weave) two interlaced fields together and display them as one progressive frame at the same time on a plasma/lcd, you lose the temporal resolution advantage of 50i. I can assure you the tenns or the football I am watching does not have the motion judder of a 25psf drama. Most would say that the best picture you can currently get is a 1920 x 1080 progressive picture displayed at it's native 24 frames/second from a bluray player. It has virtually unlimited bitrate capability. The motion artefacts you describe are nothing to do with the frame rate but created by an inadequate bitrate causing visible artefacts when the mpeg compressed signal is decoded. Mpeg works by sending 1 full frame and series of partial frames with difference info. THe encoder rebuilds the video by adding the difference info to the full frame (I frame) an inadequate sample rate produces very visible artefacts. Some channels have woefull bitrates giving rubbish pictures. |
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#44 |
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HD TV allows two transmission standards 1080i (up to 1920 horizontal res and 1080 vertical delivered interlaced at 25 frames/sec and 720P which is better for fast action, this reduces the resolution to 1280 to 720 and increases the frame rate to 50fps. 720P as the P indicates is progressive, 50fps is possible within similar bandwidth restrictions as 1080i because there is less pixels to transmit. 720P is better for motion because there is no time difference of 1/50 sec between alternate rows of pixels which gives interlaced a slightly jagged look. No broadcaster afaik uses 720P apart from video on demand like BBCi player
None of the above answers my questions above:- OK, so if the fields are displayed at the same time why is interlaced always used for sport due to it's better motion portrayal? If you look through the BBCHD commissioning requirements it says to use 50i not 25 psf for sport because "sport requires smooth motion". As I said the 50i advantages for motion portrayal are not lost after deinterlacing on my plasma. How would that be the case if the two 50i fields were simply combined into one 25frame\sec? |
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#45 |
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No broadcaster afaik uses 720P apart from video on demand like BBCi player
I just tested an NTSC DVD of 480i TV content- surprise, surprise the "average framerate rendered" is 59.94 not 29.97! This suggests that progressive displays do indeed in some way show interlaced content at either 50 or 60 fps, but probably not as smoothly as 720p/50/60 does. |
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#46 |
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We aren't talking about 720 50p.
None of the above answers my questions above:- OK, so if the fields are displayed at the same time why is interlaced always used for sport due to it's better motion portrayal? If you look through the BBCHD commissioning requirements it says to use 50i not 25 psf for sport because "sport requires smooth motion". As I said the 50i advantages for motion portrayal are not lost after deinterlacing on my plasma. How would that be the case if the two 50i fields were simply combined into one 25frame\sec? Just one of a million posts on the net http://www.zdistrict.com/2007/01/10/720p-vs-1080i/ |
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#47 |
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1080i is the only system used by any UK broadcaster not just for sport, the only alternative is 720P50. If you read my posting i said apart from electronic jiggery pokery.
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#48 |
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Given that LCDs and Plasmas are progressive, by their nature they cannot show interlaced video, so they must deinterlace the content (or the STB box does it)- what I am unclear of is whether they deinterlace to 25 frames or 50 frames per second- if it is only 25 why do they not just transmit at 1080p 25?
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#49 |
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1080i is the only system used by any UK broadcaster not just for sport, the only alternative is 720P50. If you read my posting i said apart from electronic jiggery pokery. It's entirely possible that the TV processes every other field to attempt to remove motion jaggies in exactly the same way that a 100Hz TV doubles the frame rate to 50fps.
Just one of a million posts on the net http://www.zdistrict.com/2007/01/10/720p-vs-1080i/ My question to you is if the sport (for example) produced at 50i because it has smoother motion, is simply deinterlaced into one frame 25 fps, why wouldn't it's motion suddenly suffer from the judder that afflicts film/25 psf? Can you see it's temporal resolution would be lost? That really doesn't appear to be the case on my non-frame interpolating plasma. It depends how the picture is de-interlaced. |
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#50 |
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And Sky, Virgin, Freesat etc. Only broadcast in 720p.
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