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Old August 26th, 2007, 08:30 PM   #1
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Why footage look so much worse on computer?

Curious, shot some footage (HD 1080 on Sony hc3), and plugged into the TV is plays perfect and looks great. But clips captured via Final Cut Express, played from quicktime on G5, have this sort of jumply look, that stalls a bit, and the color unlike the TV (or lcd), is flat and darker.

I'm played back from both an external Lacie and the internal Mac drive, is this the issue on speed problem? not sure why looks so terrible on computer as compared to TV or lcd.

Mac OS 10.4.10, G5 , 2GB ram, dual 1.8
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Old August 27th, 2007, 12:20 AM   #2
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From http://www.hitequest.com/Kiss/TV.htm:


Interlaced vs progressive

I don't think we should start from the very begginning, explaining how a TV works by firing a stream of electrons onto a phosphor coated screen. Just remind you, that according to the American TV standard, called NTSC, the image is made of 525 scan lines (625 in European PAL standard).Every frame has an interlaced refresh rate of 30Hz (25Hz for PAL). The interlacing is an ingenious method, invented in 1927, of breaking every image into 2 fields: first - contains only odd lines, the second field - only even lines of the image. The interlacing allowes the picture refresh rate to be doubled to reduce annoying flicker, without increasing the bandwidth required for broadcasting. The computer has video memory to assemble an entire picture and send it to the screen progressively with higher frequency. It doesn't need to be compartible with TV. This avoids the need for interlacing and results in a more stable screen image.

Resolution

Rather than dividing the screen into scan lines, a computer image is divided into dots or pixels. What kind of resolution is your monitor set for? Say it is 1024x768 pixels. How to compare it with a TV resolution? From 525 lines only 480 are visible, the rest are used for synchronization. So the vertical size of a TV image is 480 pixels. Knowing that the standard lenght/width ratio of TV screen is 4/3, the vertical size will be 640 pixels. This resolution is probably OK for 14" monitor, but on 27" monitor each pixel will have 4 time larger area!
However, don't forget about the distance you watch your TV from! A TV was not meant to be seen as close as a computer monitor.Your eyes are also part of the equation. It means that the difference in image quality between an HDTV (high-definition-television) and a regular analog TV can only be appreciated on big screens. For smaller screens the difference between a high-definition and an analog TV is hardly seen.
An HDTV monitor can display at least 720 image-carrying horizontal-scan lines in progressive mode, and at least 1080 lines in interlaced mode.

TV interface

Composite Video - also called CVBS (colour video baseband signal), contains luminance, chrominance and sync information in one signal. Look for "Video out" RCA plug on the back of your VCR.

S-Video - stands for separated video: luminance and chrominance signals are transferred separately, resulting in the greater image quality. The special S-video connector also carries left-and-right audio signals for stereo.

Component Video (YCbCr) - video signal is devided into 3 parts: Y - luminance signal (for compartibility with old monochrome TVs), Cb=0.564(B-Y), Cr=0.713(R-Y). Instead of transferring 3 chrominance signals (R,G,B ) it is easier to use just their difference (save bandwidth). Since Y is a combination of 3 major color signals, taken in the right proportion ( Y=0.587G+0.299R+0.114B), the third color component can be extracted from Y,Cb and Cr information. This method also provides high quality and eliminates cross-luminance and cross-color effects. The component video requires 3 RCA connectors.

RGB - are the 3 analog inputs for a regular CRT computer monitor. Hsync and Vsync are transferred separately.

DVI - digital video interface to transmit formatted graphics data to flat-panel displays. R,G,B signals are transferred in the digital format (8bit per signal) and accompanied by clock and control signals. Hsync and Vsync are sent over Blue channel during the inactive data portion or blanking periods.


References:
1.Harve Benoit, Digital TV,1997
2.B.Grob, Television and Video systems
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Old August 27th, 2007, 01:07 AM   #3
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Quote:
Instead of transferring 3 chrominance signals (R,G,B ) it is easier to use just their difference (save bandwidth).
This is bizarre terminology. RGB signals are not chrominance signals.
Cb and Cr (in Y'CbCr; or Pb and Pr in Y'PbPr) are generally referred to as chroma.

Y'PbPr is the correct term for analog component video, which is what is carried over 3 RCA cables.

There are other inaccuracies but I don't think there's much point in explaining why the article is wrong ("Knowing that the standard lenght/width ratio of TV screen is 4/3, the vertical size will be 640 pixels.").

Quote:
But clips captured via Final Cut Express, played from quicktime on G5, have this sort of jumply look, that stalls a bit, and the color unlike the TV (or lcd), is flat and darker.
Possible reasons:
A- Some TVs mess with the image to make it look "better". It might have modes with names like "vivid" that do this.
B- Quicktime might be applying inappropriate color management (due to programming bugs).
C- Many monitors tend to produce different colors. Consumer monitors are all over the map.
D- Your computer image is being affect by LUTs, video overlays, or inappropriate calibration.

2- Kevin, please respect other dvinfo members and don't cross post:
http://www.dvinfo.net/conf/showthread.php?t=101883

Last edited by Glenn Chan; August 27th, 2007 at 01:48 AM.
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