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background image

Temporal

Compression

Æ

Interframe

Æ

Can

use

other

frames

as

references

Æ

A

Frame

tends

to

be

similar

to

the

frame

preceding

it

Æ

So

TC

encodes

only

the

changes

in

one

frame

to

another

Æ

With

the

exception

of

key

frames

FRAME

TYPES

AND

COMPRESSION

*

A

keyframe

=

a

complete

image

compressed

using

intraframe

compression

Æ

not

based

on

any

other

frames…always

the

first

frame

Æ

important

for

random

points

as

they

the

only

frames

that

can

be

decoded

all

by

themselves

Æ

most

authoring

codecs,

like

Motion

JPEG

and

DV

use

only

keyframes

–

makes

editing

easier

*

Delta

frame

=

compressed

using

interframe

compression

+

contains

only

portions

of

the

adjacent

frame

that

are

different

Æ

For

typical

content,

a

delta

frame

might

be

only

10

‐

20%

the

size

of

the

same

frame

at

the

same

quality

as

a

keyframe

Æ

2

main

types:

P

‐

frames

(predictive

–

based

on

previous

frame)

&

B

‐

frames

(bi

‐

directional

–

based

on

previous

and

subsequent

frames)

Note:

Codecs

vary

in

how

well

they

encode

complex

frame

transitions.

For

example,

fades

up

and

down

are

very

difficult

for

some

codecs,

but

some

newer

codecs

have

code

built

in

to

handle

fades.

COLOUR

MODES

‐

Way

codecs

describe

colour

=

important

Æ

3

basic

types

of

colour

in

today’s

codecs:

«
...
24
25
26
27
28
...
»

Содержание XL1 3CCD

Страница 1: ... the lens which best suits your situation The wide angle lens is best used for establishing shots while the normal lens will be used most of the time The Canon XL1 has a Super Range Optical Image Stabiliser which is an advancement on previous stabilisers This can be done by sliding the small switch on the left of the camera and is useful for shots where there may be vibration It is however useful ...

Страница 2: ...ight situations as it allows you to have better control over the colour and light Flash photography you can attach a separate flash for flash photography but I don t think we have these Zebra Pattern This highlights contrasts allowing you to see where there s any over exposure or bad reflections so you can change them It is displayed literally with a zebra stripe pattern Four Channel Digital Audio...

Страница 3: ...situations where you may only have one tape the long play setting can increase your tape capacity by one third This does however lower the resolution A F Auto Focus if you re in manual this will auto focus for you N D Filter Neutral Density Filter this automatically chops down how much light the iris accepts through the lens it decides itself when it needs to be used the sun light will flash to te...

Страница 4: ...e greater the shutter speed the more distinct the frames are for playback Manipulating the shutter is useful for manipulating the depth of field Depth of field used properly marks the difference between amateur videomakers and professionals dB the ratio of units of noise which is measured in Dbs By using this you can make your scene lighter darker than the limit this is useful at night like pumpin...

Страница 5: ...lets in more light while a higher number lets in less light Æ In terms of DOF As you go higher you maintain DOF Smaller numbers allow more things to be in focus Higher numbers allow greater DOF meaning the main object is in focus and the others aren t Summary Æ Wide Iris Shallow DOF Æ Small Iris Greater DOF Tip Be careful of playing with the iris in daylight you can t push up the iris too much whe...

Страница 6: ... manipulate your picture What it s for To get the maximum amount of light coming through in difficult lighting situations Essentially playing with the shutter is a manipulation of the frame rate How it works The higher the shutter speed the choppier the image and the lower the shutter speed the smoother the image Æ in both of these scenarios having the shutter speed too high or too low can result ...

Страница 7: ...reversed with the forehead being more prominent the opposite effect would be achieved 2 Medium In this shot there s more space at the bottom than at the top of the frame This type of shot generally validates the subject more If this shot was reversed with less space at the bottom and more at the top then the opposite effect would be achieved the subject would look weaker and more subservient Be ca...

Страница 8: ... be broken up into three shots Æ this provides your editor with shots to work with still move still Tip Cover up any zooms you may need to do with pans A good cameraman will practice until the zoom is virtually imperceptible underneath the pan ...

Страница 9: ...nalogue or digital VIDEO AUDIO CONTROL Kettle Plugs These can be either mini or full size Identification These are your standard kettle looking cables so called because that s what they were originally used for Usage Kettle plugs are control cables which carry the power to control specific devices BNC Cable Identification This is the cable with the round head the metal prong in the centre plastic ...

Страница 10: ...rd with the computer fitting bit on one end and the USB cord looking bit on the other There are three types of Firewire cables namely 4to 6 4 to 4 and 6 to 6 these numbers refer to the size of the end bits we use 4 to 6 aka small to big There are two speeds namely 400 and 800 We use 400 800 is for more modern machines or Macs and this is the same speed as a USB 2 port Usage For video and audio use...

Страница 11: ...f the silver point indicates a stereo jack Additional info about the BNC cable an extra piece of hardware can be used with this cable to split the signal This is known as the BNC T piece It is a T shaped device that you plug into the end of the BNC cable and it takes the video signal and sends it to more than one device useful if you want to broadcast on multiple monitors The only drawback with th...

Страница 12: ...und 1 XLR Identification This is the male to female cable which has three prongs on one side and three holes on the other Usage It operates on three channels which are common left and right Features Therefore this cable can take stereo 2 Jack also get mini jack and mini mini jack Identification This is a jack and has the jack looking silver prong attached to a cable Usage The females are plugs and...

Страница 13: ... A rifle mic is directional and so named because of its shape A rifle mic is best used in situations where there is background noise and one wants to focus on one specific sound To get optimum sound it is good to use the rifle mic in conjunction with the shure mixer in the following way camera Shure mixer Rifle mic A green cable runs between the camera and the shure mixer and a yellow cable runs b...

Страница 14: ... for getting good sound For callabration press the tone button on the shure mixer and once you hear the tone set the master dial to 4 Switch Audio 1 on the camera to maual in order to change the frequency Set the level on the camera to 12 It will be highlighted in a box on the dial Switch the tone switch off once it is set Making the Mic Stereo In order to check that the sound is working with bout...

Страница 15: ...o the number of times per second the wave goes through a cycle The more cycles per second the higher the frequency Æ The amplitude goes from soft to loud and refers to the swing of the curve The further the curve swings above or below the centre line the louder the signal together frequency amplitude make up the sine wave The average ear processes 20 20Hz to 20 000 cycles per second Æ the waveleng...

Страница 16: ...So whatever the bit system is multiply by 6 to get its range e g a CD 16 bit so it s 96dB DIGITAL FEATURES Copying a signal degrades it but not in digital reproduction Digital has no wow or flutter because the buffer circuit smooths out speed variations A D converter Æ in this conversion process the quality is affected by 2 variables 1 Sample rate the higher the sample rate the better this gives y...

Страница 17: ...and 2 Æ For sound checks PROCEDURE Audio input 2 channel recording Stereo 2 using mini jacks Mic supplied sound source ext mic plugged into mini jacks Tip ATT AttentuatorÆ useful for loud environments reduces noise for more natural sound Audio 1 Input for 2 channel recording Stereo 1 using RCA jacks Sound source VCR CD Audio Input for 4 channel recording Stereo 1 and 2 simultaneous Using RCA jacks...

Страница 18: ...rativised Æ More neutral colour temperature Examples include magazine covers TIP White umbrella technique this scatters the rays of light and is good if you ve only got one light 2 Standard Three point interview Æ Not very stylised Æ Often used for documentaries Æ Good for giving the correct depth and features of subject Æ Uses three points of light as follows ...

Страница 19: ...Back Æ the back light gives depth and this can be altered by angling it higher Key Fill subject Æ the key light is the strongest light and sits at about a 45 degree angle ...

Страница 20: ...with their ridiculous power not the best option for shooting in a rural school or the like Redheads These are less powerful more versatile lights which you would take into the field Gels the coloured plastic papers which you put over a light to change its tone Scrim the clear gel paper which you put over a light Gobo a shortening of go between this is a medium between the light and the subject whi...

Страница 21: ...specially the paler ones we found it useful to try out a yellow gel to make the shot look more natural This was especially helpful in our night shot placed on the fill light When lighting shots to mimic night time it is useful to use blue gels to give the effect of moonlight One has to play around to get it right but we ended up using a number of blue gels to create a darker blue colour THE CAMERA...

Страница 22: ...owing data rates and storage requirements for different DV media types BITSTREAM TYPE DATA RATE TIME ON 1 700MB CD ROM Uncompressed high definition 1920 x 1080 29 97 fps 745750 7 5 seconds Uncompressed standard definition 720 x 486 29 97 fps 167794 33 seconds DV25 miniDV DVCAM DVCPRO 25000 3 min 44 seconds Typical DVD 5000 18 min 40 seconds VideoCD 1167 80 minutes Broadband web video 100 2000 3 ho...

Страница 23: ...d a type of compression may be used in multiple formats But most standard video formats include requirements that specify compression types and data rates DVD FORMATS Extremely popular format With technological developments DVD capacities are increasing A DVD that plays in a DVD player a DVD Video One that plays in a computer DVD ROM specifically computer formatted disc Hybrid DVD Video DVD ROM di...

Страница 24: ...e devices have small screens and slow processors even compared to a laptop computer but the ability to play video back on extremely small and lightweight devices can have great value Most compressed video formats can be played on some mobile devices including Adobe Flash Video MPEG 4 Microsoft Windows Media and RealMedia Dedicated mobile formats like Kinoma are also available There are no universa...

Страница 25: ...ing end decoding the compressed data so that it can be presented to the viewer It s important that the pair be matched because the decoder decompressor needs to understand the encoder s compressor s summary of the data TYPES OF COMPRESSION Video codecs can use spatial compression temporal compression or a combination of both Spatial Compression Æ Intraframe Æ Affects only a single frame at a time ...

Страница 26: ...tion JPEG and DV use only keyframes makes editing easier Delta frame compressed using interframe compression contains only portions of the adjacent frame that are different Æ For typical content a delta frame might be only 10 20 the size of the same frame at the same quality as a keyframe Æ 2 main types P frames predictive based on previous frame B frames bi directional based on previous and subse...

Страница 27: ... critical luma information at full resolution and use less resolution for the chroma information Æ Greatly reduces data rate and processing requirements You can convert RGB to and from Y CbCr adequately but there are always some colors that are available in one mode but not the other and there can be rounding errors as part of the conversion By working in tools that support 16 bit per channel RGB ...

Страница 28: ...ccuracy per channel than 8 bpc color when converting to or from 16 bit per channel RGB in After Effects 6 16 and 32 bpc Æ Some high end applications use 16 bpc or 32 bpc colour to preserve more colour detail Æ especially useful when you have a multi step authoring process need to apply visual effects to your images or when you convert from and then back to Y CbCr COLOUR SAMPLING Color sampling rec...

Страница 29: ... its own sample however it can result in visible chroma artifacts in areas of high saturation yUV 9 This format has one chroma sample per 4 x 4 block of pixels Æ results in noticeably degraded quality so it isn t used in modern codecs Audio Compression The most fundamental factor in audio is sampling rate which is measured in Hertz Hz or cycles per second Audio CDs use 44100 Hz or 44 1 kilohertz K...

Страница 30: ...riginally multimedia audio used 8 bit sampling measurement of volume from 0 255 for each sample Æ produces fairly poor quality audio 16 bit sampling Æ current standard for audio distribution Most modern codecs and all audio CDs use 16 bit sampling as well 20 bit sampling Æ used for professional audio recording to provide a better dynamic range than 16 bits 24 bit sampling Æ rapidly becoming the st...

Страница 31: ...s are required to reach a particular quality level Æ When improving compression efficiency you can choose to lower the data rate while keeping the quality the same increase the quality while keeping the data rate the same or pick a point in between Æ Typically the higher the data rate the smaller the quality differences Authoring video for future compression One key to high quality compression is ...

Страница 32: ...e higher quality output for progressive scan monitors 2 Camera motion Camera motion changes every pixel of every frame Lack of camera motion is the simplest of course But modern codecs can encode camera motion such as that created using dollies quite well Tilts and pans are more difficult Depending on the codec rotating the camera a Dutch can be trivial or extremely costly in compression efficienc...

Страница 33: ...speed introduces motion blur that helps compression you can use the virtual shutter in rendering applications For effects that support motion blur render them with a shutter speed that matches that of the source 3 Anti aliasing This rendering technique softens the edges of rendered elements letting a pixel at the edge of an area be an intermediate value Smoothing out transitions among parts of the...

Страница 34: ... image data Ranges greatly in quality but is inherently susceptible to visual interference from electronic noise and suffers attenuation or the loss of signal power and quality over long cable runs usually 300 meters or more Equipment that supports analog signals is generally more affordable Because computers only use digital data the analog source must be converted to a digital copy to be capture...

Страница 35: ...y 100 feet or less Some types of professional and broadcast equipment use two BNC cables one for luma and one for chroma to carry S Video signals This setup provides a connection that can be run farther and that can be locked into place to prevent the cable from falling out and losing the signal Component analog Also known as YUV Y for luminance U for one chroma channel and V for the other chroma ...

Страница 36: ...nector is common to high end headphones and is standard on most home stereo equipment Similar but smaller is the eighth inch connector that is standard for portable audio devices and computer sound cards Balanced audio This type of connection consists of two wires which serve to balance the signal and a shield A balanced connection is far less susceptible to interference so it is possible to maint...

Страница 37: ...duce a DV signal that is almost as good as component analog video at the same DV data rate because of better recording technology The DV format includes a series of computer style 1s and 0s and no analog The data on the computer is exactly the same data as on the tape so the result is a perfect copy Many nonlinear video editing applications like Adobe Premiere Pro can read and edit this format nat...

Страница 38: ...g connection cables Digital video carries an embedded digital audio signal with the digital video signal The most common professional grade digital audio format is Audio Engineering Society European Broadcasting Union AES EBU A stereo channel of AES EBU can be transmitted over single BNC or single XLR connection cables Choosing the right capture codec When you capture content you must choose an ap...

Страница 39: ...ple volume encoding to multiple output formats it is useful to export an intermediate file from the timeline and use the exported file for further processing Æ Exporting to file A file you export for later processing is called an intermediate file Reason for this to provide high quality in the most useful format without introducing any compression artifacts Æ Choosing whether to preprocess or to a...

Страница 40: ... format Æ Choosing a codec for exporting When you export an intermediate file pick a codec and a data rate that doesn t introduce compression artifacts When you are not preprocessing it s typical to use the source codec or Motion JPEG When you use Motion JPEG use it in single field when you export as progressive scan or interlaced when you export as interlaced For AVI files on Windows the Huffyuv ...

Страница 41: ...xactly 24 frames per second fps progressive scan which doesn t convert to the 59 94 fps of NTSC or the 50 fps of PAL Converting from film to PAL is easy The video is sped up 4 to 25 fps and converted into progressive PAL NTSC is a little more complex to perform The film is first slowed down to 23 976 fps and then it is converted to the 59 94 fps by using 3 2 pulldown The first frame of film become...

Страница 42: ... SVCD and with different shapes for MPEG 2 for SVCD Conversely most web video formats use square pixels which makes it easier to do the math The key to getting aspect ratio correction right when you convert to square pixel sources from nonsquare pixel sources is to make sure that the output frame size matches the source aspect ratio Noise reduction Removing noise especially grain from an image mak...

Страница 43: ...t optimum results for the project It s most important to understand the goals that the compressed video is meant to achieve Æ Choosing a data rate mode Data rate modes include average limited the most common type of data rate limitation In this mode you specify the average data rate and the codec tries to make sure that the file ends up at the requested average The codec varies the rate up or down...

Страница 44: ...nk of the file has a data rate at or below the target data rate Most streaming encoded files use both average limited and buffer limited encoding Buffer limited encoding is often called constant bit rate or CBR Quality limited encoding different from the other methods because it doesn t specify a data rate Instead it specifies a quality target and each frame uses as many or as few bits needed to r...

Страница 45: ... third Because there are fewer pixels pixel quality becomes more important Most codecs and formats require the height and width of a video to be divisible by two and give best compression efficiency when height and width are divisible by 16 Æ Specifying aspect ratio An important facet of frame size is aspect ratio Most web and CD ROM formats use square pixels and many formats only support square p...

Страница 46: ... would normally allocate to a given frame aren t sufficient to hit the target quality it raises the data rate for the frame to the minimum required for quality then drops one or more frames that follow to keep the average data rate on target Æ Whether this process is appropriate depends on the content Æ Various factors come into play here Keyframe rate Sample rate Channels Delivery methods for vid...

Страница 47: ...time streaming However progressive download can t provide reliable real time performance the whole buffering thing Progressive download is the easiest cheapest and most forgiving type of web video to author and deploy Æ Real time streaming Offers the traditional experience of seeing the video after only a few seconds of buffering but it risks image glitches poor quality and limiting the data rate ...

Страница 48: ...ion that requires you to provide multiple versions of the content or exclude some platforms The most commonly deployed players are Windows media Player 6 4 Windows and Windows nt Windows media Player 9 and later Windows Windows media Player 9 for mac os X 10 1 and later Windows media Player mobile Windows media Player for Pocket PC 2002 WMP for Pocket PC 2000 Windows media video codecs Æ Windows M...

Страница 49: ...ata rate from which audio data rate is subtracted to leave video data rate However some tools don t use this method You can use realmedia for streaming delivery Æ Unlike Windows Media it can mix and match codecs in different streams All streams must share the same frame size which can limit scalability You can use realmedia for progressive download Æ While RealMedia is mainly considered a streamin...

Страница 50: ...ats a RealAudio codec is defined by a combination of a codec data rate sample rate and channels Instead of picking a codec and other parameters the user picks an inclusive combination Another twist with the RealMedia audio support is that many tools require audio codecs to be specified for video and music content for both video and audio files and audio only files The user picks the one based on t...

Страница 51: ...pport multiple formats provide the rate in Kbits Quicktime can be used for real time streaming progressive download and disc based delivery Quicktime video codecs Given the long heritage of QuickTime for flexibility and support for third party codec vendors the range of codecs supported in QuickTime is broader than in the other formats However the best codecs are often not provided for free Below ...

Страница 52: ... you set the data rate if controllable in the Options dialog box The following are QuickTime audio codecs MPEG 4 QDesign music 2 QDesign music 2 Pro Qualcomm PureVoice IMA MP3 None 24 and 32 bit integer Floating point Exporting One has the following exporting options MPEG 1 format DVD and mPeG 2 formats MPEG 4 format AVI format ...

Страница 53: ...re introduced with Windows Media 7 wmv Æ A Windows Media Video file wmv is an asf file that contains video wma Æ A Windows Media Audio le wma is the same as an asf file but it only contains audio asx Æ An asx file is a metafile for Windows Media Streaming The asx file goes on the web server and points to the media on the streaming server The asx file format itself hasn t changed but with the adven...

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