Colorimetric and Resolution requirements of cameras

Colorimetric and Resolution requirements of cameras

Colorimetric and Resolution requirements of cameras

Alan Roberts

ADDENDUM 18 rev.1 : Assessment of, and settings for, Panasonic

HVX200

Data for this section is taken from short examinations of two production models of the Panasonic HVX200 camcorder. This is a HDTV camcorder, physically very similar to the standard-definition DVX100, with 3

” ccds, the manual gives no clue as to the sensor resolutions. The two models under test ran only at 60 Hz

(actually 59.94) or 50Hz. It records HDTV using the DVCProHD algorithm onto P2 flash cards (1080i,

1080psf, 720p), SDTV using any of the DVCPro50 or DVCPro or DV algorithms onto P2 cards (480i,

480psf, 480psfa* or 576i, 576psf, 576psfa), and SDTV onto miniDV. It can also shoot “off-speed” when recording 720p onto P2 cards, but only at spot speeds, it is not continuously variable as is the Varicam AJ-

HDC27F.

The camera is relatively light and has an integral lens and viewfinder, with side lcd panel, and seems aimed at the high-end consumer/professional market rather than full broadcast, which would normally demand interchangeable lenses. It is the first tapeless camcorder for HDTV. It has a photographic speed of about

640ASA.

It has the usual internal menus for setting the performance, not as complex as in the 720-line Varicam or the

1080-line HDX400, but enough to control most of the important features. It is not suited to multi-camera operation. It has analogue-only video outputs (components at both HD and SD via a multi-pin connector) and digits via IEEE1394 Firewire and USB. This alone puts the camera in the consumer/semi-pro market, rather than broadcast, which would normally expect either HDSDI or BNC connectors for analogue.

The same assessment procedure was used as for other HD cameras, partly attempting to get a good “filmlook”, and the settings reflect that. It is useful to think of the camera, when used in this way, to be mimicking a film camera and telecine, with “best light” transfer to tape, with about 10 stops of tonal range.

Assuming that a grading operation will be used in post-production, the settings attempt to give the colourist the same range of options as with film. The recommended settings allow about 1.3 stops of over-exposure and one of under-exposure relative to normal operation. This is not as good as can be achieved in 2”/3 cameras, and arises from the difference in pixel size (the pixels here are much smaller, so sensitivity is maintained at the expense of highlight handling and video noise).

This revision corrects some minor typographical errors, none of which have any effect on picture or sound quality.

1

Colorimetric and Resolution requirements of cameras

Alan Roberts

ADDENDUM 18 rev.1 : Assessment of, and settings for, Panasonic

HVX200

The assessment of this camcorder was aimed mostly at discovering what it could do, rather than deriving a preferred setting, results are given in Section 2. The controls are not as flexible as for full “broadcast” cameras, so it may or may not be possible to derive a specific “film-look” for it. However, there is sufficient flexibility to achieve much of what is desirable in “film-look” settings. Photographic “speed” is about

640ASA.

Many of the menu items have little or no effect on image quality. Those that have significant effect are highlighted. The full set of menu items is given for completeness. In boxes with a range of numeric settings, e.g. -99~99, the values indicate the range, and zero means no alteration to factory setting, not zero effect, and no scales are given. For each item, the factory setting is given if it is known, and the range offered by the camera under test. “BBC” settings are in the last column, where appropriate. The following table shows the menu settings when the camera is in “Camera” mode, these affect picture performance; other menus are included for completeness. Values that are underlined are the factory default settings. The menus share some features with the Varicam, in that Scene Files store a great deal of information, permitting widely different settings to be stored.

BBC-preferred values are given for SD operation, for 1080 interlaced and psf, and for 720 film and sport

(where sport covers all uses that are not intended to look like film). Items that have an important affect on picture appearance are highlighted. Some items are valid only for tape- or P2-operation, all items are flagged.

It is unfortunate that the colour bars that the camera generates are only 100/0/75/0 (i.e. EBU) rather than the much more useful SMPTE bars that are ubiquitous in HDTV.

This revision corrects some minor typographical errors, none of which have any effect on picture or sound quality.

This is not intended as a replacement for reading the manual.

1

Menus and Settings

CAMERA MENU

SCENE FILE

CAMERA SETUP

SW MODE

AUTO SW

RECORDING SETUP

AV IN/OUT SETUP

DISPLAY SETUP

CARD FUNCTIONS

OTHER FUNCTIONS

OPTION MENU

MCR/VCR MENU

RECORDING SETUP

PLAYBACK FUNCTIONS

AV IN/OUT SETUP

DISPLAY SETUP

OTHER FUNCTIONS

OPTION MENU

Camera operational controls, needs lab work to get the best from these

Basic camera setup controls

Configuration of switches

Control of camera automatic features

Tape and P2 card controls

Configure audio/video connections

Viewfinder and LCD panel settinmgs

P2 flash card controls

Sundries that don’t fit anywhere else

Control of IEEE1394 (Firewire) connection

Timecode, IEEE1394, User bits audio, etc

Audio matters

Analogue connection and IEEE1394 settings

Viewfinder and LCD panel settings

Sundries that don’t fit anywhere else

Control of IEEE1394 (Firewire) connection

2

DUBBING MODE MENU

RECORDING SETUP

DUBBING SETUP

Timecode, IEEE1394, User bits audio, etc

Format, pulldown etc

CAMERA MENU

SCENE FILE (1-6) mode range comments BBC

Operation type (P2, tape) Camera Video/Film

Also sets SynchroScan indicator to time or angle

Frame rate (P2) Camera

60 12, 18, 20, 22, 24, 26,

30, 32, 36, 48, 60

50 12, 18, 20, 23, 25, 27,

30, 32, 37, 48, 50

Shooting speeds for 720p only

Synchro scan (P2,tape)

Detail level (P2,tape)

V Detail level (P2,tape)

Detail coring (P2,tape)

Chroma level (P2,tape)

Chroma phase (P2,tape)

Color temp (P2,tape)

Master Ped (P2,tape)

A. Iris level (P2,tape)

News gamma (P2,tape)

Gamma (P2,tape)

Knee (P2,tape)

Matrix (P2,tape)

Skin tone detail (P2,tape)

V Detail freq (P2,tape)

Name edit (P2,tape)

Camera

Camera

Camera

Camera

Camera

Camera

Camera

Camera

Camera

Camera

Camera

Camera

Camera

Camera

Camera

Camera

Save/init (P2,tape) Camera

CAMERA SETUP mode

1/n~1/249.8

-7~+7

-7~+7 n=frame rate, or degrees for FILMCAM, will not set longer than 1/field or frame

Horizontal and vertical edge detail

0 (1080i)

-2 (1080p)

+2 (720sport)

Vertical edge detail

-4 (720film)

0 (SD)

-2 (1080i)

-4 (1080p)

+3 (720sport)

0 (720film)

-2 (SD)

-2~+7

-7~+7

-7~+7

-7~+7

-15~+15

-4~+4

On/Off

HDnorm, Low,

SDnorm, High,

B.press, Cine-likeD,

Master black lift

Auto iris gain

Adds some extra knee to cope with highlights

HDnorm= ITU709, Low=high contrast

(skin press), SDnorm=DVX100,

High=black stretch, B.press crushes,

Cine-lineV CineV=more contrast than CineD

Auto, Low, Mid, High Reaches ~ 250%, knee at 80%,90%, 100%

60 Norm, Enriched, Fluo,

Cine-like

50 Norm1, Norm2, Fluo,

Cine-like

Not specifically tested

On, Off

Thin, Mid, Thck

Save, Initial

Noise limiting for detail

Saturation

Hue

Fine white balance offset

Reduces skin detail

Thin and Mid may cause twitter

Names the selected scene file

Save changes, or factory reset

range comments

+4

0

0

Off

HDnorm

(HD),

High (SD)

90%

Norm/

Norm1

Off

Thin

BBC

Aspect conv (P2,tape)

Setup (P2)

Setup (tape)

Mid gain (P2,tape)

High gain (P2,tape)

ATW (P2,tape)

Handle zoom (P2,tape)

Iris dial (P2,tape)

SW MODE

Camera

Camera 60

Camera

Normal, Letter box,

Squeeze

0%, 7.5%

Camera 60

Camera 60

0%, 7.5%

0, 3, 6, 9, 12dB

Camera 60 0, 3, 6, 9, 12dB

Camera 60 Ach, Bch, Prst, Off

60 L/Off/H, L/M/H,

L/OFF/M

Camera 60 Down open, Up open

mode range

Recording format for 480-line

Composite black level for NTSC output

Composite black level for NTSC output

12dB gain is fairly noisy and visibly soft, probably not acceptable

Assign AutoTrackWhite to gain switch

Set zoom speed switch settings,

Reverses iris control (when Manual)

comments

3dB

6dB

BBC

3

User 1,2,3 (P2,tape) Camera

RecCheck, Spotlight,

Backlight, Blackfade,

Whitefade, ATW,

ATWon/off,

Gain18dB,

FocusRing,

IndexMemoP2,

SlotSelP2,

ShotMarkP2

Assign user switches.

18dB works only with 60Hz formats, and not with slow shutter.

P2 options label shots, change slots etc.

Default:1=Whitefade, 2=Backlight,

3=Index/Memo

AUTO SW

A.Iris (P2,tape)

AGC (P2,tape)

ATW (P2,tape)

AF (P2,tape)

RECORDING

SETUP

Rec format (P2)

Rec format (tape)

480i rec mode (P2)

576i rec mode (P2)

Rec function (P2)

One-shot time (P2)

Interval time (P2)

Prerec mode (P2)

Rec speed (tape)

Audio rec (tape)

Mic alc (P2/tape)

Mic gain 1 (P2/tape)

Mic gain 2 (P2/tape)

25M rec ch sel (P2)

1394 TC regen (P2/tape)

TC mode (P2/tape)

TCG (P2/tape)

First rec TC (tape)

TC preset (P2/tape)

mode

Camera

Camera

Camera

Camera

mode range

On, Off

6dB, 12dB, Off

On, Off

On, Off

comments

Auto iris

Set auto gain maximum

AutoTrackWhite

AutoFocus, disables Focus/Push Auto

range comments

Camera

Camera

Camera

60

50

60

50

60

50

1080i/60i, 1080i/30p, 1080i/24p,

1080i/24pa

1

, 720p/60, 720p/30, 720p/24,

720p/30pn

2

, 720p/24pn, 480i/60i, 480i/30p,

480i/24p, 480i,24pa

1080i/50i, 1080i/250, 720p/50p, 720p/250,

720p/25pn, 576i/50i, 576i,25p

480o/60i, 480i/30p, 480i/24p, 480i/24pa

576i/50i, 576i/250

DVCPro50, DVCPro,

DV

Recording format for

P2 card, this terminology is nonstandard, but the meaning is clear.

Tape recording format

Tape compression system

Camera

Camera

Camera

Camera

Normal, Interval, One shot, Loop

1F, 2F, 4F, 8F, 16F,

1s

2F,4F,8F,16F, 1s, 2s,

5s, 10s, 30s, 1m, 5m,

10m

On, Off

Camera/

Vcr/Dub

Camera,

Vcr

Camera

SP, LP

32k12bit, 48k/16bit

On, Off

-50dB, -60dB

-50dB, -60dB

2ch, 4ch

On, Off

Camera

Camera

Camera

Mcr/Vcr

Camera/

Mcr/Vcr

/ Dub

Camera/

Mcr/Vcr

/ Dub

Camera/

Vcr/

Dub

Camera/

Mcr/Vcr

/ Dub

60 DF, NDF

Free run, Rec run

Regen, Preset

Non-standard recording functions

Frames or time to record

Frames/seconds/minutes

Memory cache for prerecording

Tape speed

The usual

Auto level control

External mic level control

External mic level control

DV/DVCPro25 sound channels

On=TC from 1394, Off=other controls

Only relevant in the 59.94Hz variant, 24p uses NDF

TC runs free or only when tape runs

Select TC used at start, Regen reads tape and continues

Set initial TC, when recording 24p, set frame to multiple of 5 for it to make sense

BBC

BBC

________________________________________________________________________________________________

1

psfa is the slightly improved variant of the 2:3 pulldown process used to derived 60 fields from 24 frames.

Conventionally, 2 fields are made from one frame, then 3 fields from the next; this results in video frames grouped in sequences of 5, only two of which contains only information from one source frame, the others contain information from 2 source frames. In this variant, the pulldown sequence is 2:3:3:2, such that only 1 video frame in a group of 5 contains information from 2 source frames. This solves many problem in production and distribution, while somewhat attenuating the uneven progress of motion caused by the 2:3 process.

2

pn mode records only new frames, for over/undercranking, i.e. there is no frame repetition.

4

1394 UB regen (P2/tape)

UB mode (P2/tape)

UB preset (P2/tape)

1394 In preset (P2/tape)

PLAYBACK

FUNCTIONS

32k audio (tape)

Audio out (P2)

Audio out (tape)

PLAYBACK

FUNCTIONS

Mcr/Vcr

Camera/

Mcr/Vcr

/ Dub

Camera/

Mcr/Vcr

/ Dub

Mcr/Vcr

mode

Vcr

Mcr.Vcr

mode 60

On, Off

User, Time, Date,

TCG, FrmRate

On, Off

range

ST1, ST2, Mix

Ch1Ch2, Ch1, Ch2,

Ch3Ch4, Ch3, Ch4

range

Format sel (P2)

Pulldown sel (tape)

Setup (tape)

Dub

Dub

60

60

DUBBING SETUP mode 50

Format sel (P2)

Dub

Dub

Pulldown sel

Setup

Dub

Dub

AV IN/OUT

SETUP mode

Cmpnt out sel (P2)

HP mode (P2,tape)

A.dub input (tape)

Zebra detect 2 (P2,tape)

Camera/

Mcr

Camera

Vcr

1394 out (tape) Vcr

DISPLAY SETUP mode

Zebra detect 1 (P2,tape) Camera

Camera

60

60

Marker (P2,tape)

Safety zone (P2,tape)

Video out OSD (P2,tape)

Date/Time (P2,tape)

Level meter (P2,tape)

Zoom, focus (P2,tape)

Card/Tape, Batt (P2,tape)

Other display (P2,tape)

Camera data (P2,tape)

LCD backlight (P2,tape)

LCD set (P2,tape)

Camera

Camera

Camera

Camera/

Mcr/Vcr

Camera/

Mcr/Vcr

Camera

Camera/

Mcr/Vcr

Camera/

Mcr/Vcr

Mcr/Vcr

Camera/

Mcr/Vcr

Camera/

Mcr/Vcr

60

50

1080i/60i, 1080i/30p,

1080i/24p,

1080i/24pa, 720p/60p,

720p/30p, 720p/24p,

720p30pn, 720p/24pn

24p, 24pa

0%, 7.5%

range

1080i/50i, 1080i/25p,

720p/50p, 720p/25p,

720p/25pn

24p, 24pa

0%, 7.5%

range

720p, 1080i, 480i

Live, Recording

Mic, A.In

On, Off

range

50%~105% by 5%

50%~105% by 5%,

Off

On, Off

Off, 90%, 4:3

On, Off

Off, Time, Date,

Time&Date

On, Off

Off, Number, mm/feet, mm/mm

On, Off

Off, Partial, All

On, Off

High, Normal

Source of UserBits

FrameRate uses a code, refer to manual

Set info, select User in UB mode

Sync TCG to 1394 when TCSet pressed

comments

Route stereo 1/2 or 3/4 to output when 32k

Channels 3 and 4 available only on P2 recording

comments

Clip format for dub playback

23 or 2332 pulldown to 60

Composite setup for NTSC

comments

Clip format for dub playback

2:3 or 2:3:3:2 pulldown

comments

720p converts only to 1080i

Headphone feed, use Live for off-speed

Take sound from mics or audio I/O

On feeds analogue inputs to 1394, adc

comments

Default 80%, left-leaning zebra

Default 100%, right-leaning zebra

Press Zebra button to display markers

Screen info to video output, beware, it goes to 1394 as well

What to show on screen

Audio levels on screen

Show real distances (maybe☺)

Remaining capacity

Display info depth

Show camera settings on playback

Brightness

Panel, set brightness, contrast, colour

BBC

BBC

BBC

BBC

BBC

5

EVF set (P2,tape)

Self shoot (P2,tape)

EVF mode (P2,tape)

Display aspect (P2,tape)

EVF color (P2,tape)

CARD

FUNCTIONS

Scene file (P2)

User file (P2)

SD card format

OTHER

FUNCTIONS

Remote (P2,tape)

1394 control (P2,tape)

1394 cmd sel (P2,tape)

End search (tape)

PC mode (P2)

Rec lamp (P2,tape)

Access led (P2)

Beep sound (P2,tape)

Clock set (P2,tape)

Time zone (P2,tape)

Power Save (P2,tape)

Language (P2,tape)

User file (P2,tape)

Hour meter

OPTION MENU

1394 status (P2,tape)

1394 config (P2)

Camera/

Mcr/Vcr

Camera

Camera/

Mcr/Vcr

Camera/

Mcr/Vcr

Camera/

Mcr/Vcr

mode

Normal, Mirror

On, Auto

Auto, 4:3

On, Off

V/F, set brightness, contrast, colour

For when panel is forward-facing

Auto switches off V/F when panel is open

Widescreen always appears letterboxed

For black/white V/F

Camera

Camera

Camera

mode range

Read, Write

Read, Write

comments

Save up to 4 scene files to P2 card

Save up to 4 file settings (not Scene) to SD card

range comments

Camera/

Mcr,Vcr

Vcr1, Vcr2, Off Remote control access

Camera Off, Ext, Both Chain

Backup via 1394, Ext controls remote deck with Start/Stop, Chain uses remote deck as extra recorder

Camera/

Vcr

Camera/

Mcr

RecP, Stop

Blank, Rec End

Camera/

Mcr

USB device, 1394 device, 1394 host

Camera Off, Front, Rear, Both

Camera/

Mcr

On, Off

Camera On, Off

Set remote deck to stop or pause

Search for unrecorded slot or last recording

1394 host controls external deck for backup

Card access indicator

Camera/

Mcr/Vcr

Camera/

Mcr/Vcr

Camera

Camera/

Mcr/Vcr

Camera/

Mcr,Vcr

-12~+13

On, Off

English, Japanese

Load, Save, Initial

Warns of card/tape full, no tape, condensation, problem

Set clock and calendar. Really, honest, that’s what it does

Time zone offset from GMT, for foreigners

Disables 5-minute inactive shut-down

Menu language, use with care

Power down/up to activate change

Camera/

Vcr

Shows head hours (5 digits per hour)

Press Disp/Mode Chk button and Menu, then Menu to cancel

mode range comments

Camera/

Mcr/Vcr

P2: Format, rate, 50/60, channels, speed, status, video, audio

Tape: Format, rate, 50/60, channels, speed, mode, Rx, Tx

Camera/

Mcr

Dflt, 1~255 1394 extended menus

BBC

BBC

BBC

6

2

Measurement results

The HVX200 has no built-in test signal generator. This alone sets it apart from most professional and broadcast cameras. Thus all measurements had to be made the hard way, using optical test cards and an awful lot of data processing. Only the 50Hz version was measured in detail, serial number C6TC0015-R.

2.1

Transfer characteristic (gamma-correction)

Measurements were made to determine the equations of two of the gamma-correction curves, which also revealed the nominal exposure range of the camera. A Macbeth (Fig.1) chart was evenly illuminated, and recordings made at the full range of exposures.

The bottom row of colour patches on the chart forms a grey scale, and the optical density of each patch is given in the specifications of the card, thus it was possible to obtain a large number of measurement points to form a point-wise plot of the gammacorrection curves. Since the iris control is continuous, it was not possible to set exposure precisely for each exposure, nevertheless, judicious adjustments in the data processing has provided a reasonable data set from which to estimate the gammacorrection curves.

1.1

1

Fig. 2 shows data points for the Hdnorm curve (supposed to be the ITU.709 curve) with

Knee

set to Mid (which is supposed to break at 90% voltage). It is relatively easy to fit a curve to these points, but it is not easy to be accurate since there is clearly some inconsistency in the data, caused by video noise, slightly uneven illumination, lens vignetting when fully open, imprecise setting of the iris, and so on.

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

0 0.2

0.4

0.6

0.8

1 1.2

1.4

1.6

Figure 1, Macbeth chart

1.8

2 2.2

2.4

Figure 2, HDnorm gamma, Knee=Mid

The ITU.709 curve, the standard for all HDTV cameras is:

V

= 4 .

5

L

for L<0.018, else

V

= 1 .

0099

L

^ 0 .

45 − 0 .

099

The found equations for the Hdnorm curve are:

V

= 4 .

5

L

for L<0.03, else

V

= 1 .

05

L

^ 0 .

5 − 0 .

05

This is a reasonable match to ITU709, but is not perfect. The Knee causes the curve to break at signal levels of 80% (Low), 90% (Mid), 100% (High) and then extend to and exposure limit of 2.5 (250%) before clipping occurs at about 107%.

The contrast range for these settings is derived from the equations. The maximum exposure the camera can handle is 250%, while the minimum exposure that is visible in the output can be defined as that which causes the signal voltage to be 2% of the coding range (the video level of the super-black bar in SMPTE colour bars, used for setting display black level). If the noise is low, then a lower point can be taken, 1% would be the normal minimum considered relevant. For the Hdnorm curve, these ratios are approximately 550:1 (9.1 stops) and 1100:1 (10.1 stops), not bad for a camera in this category. Measurements of the High (Black

Stretched) gamma-correction curve were surprising, the found equations are:

V

= 5

L

for L<0.02, else

V

= 1 .

25

L

^ 0 .

33 − 0 .

25

7

However, the numbers in this equation are a little extreme, so in a second search a rather better match to the data was found by fitting the BBC 0.4 law to it:

V

= 5

L

for L<0.02262, else

V

=

( (

L

− 0 .

037703

) (

1 − 0 .

037703

) )

^ 0 .

4

Both these curves fit the data well, but the BBC curve (which was designed for SDTV use) seems more natural, and is presumably intended to be so. This gamma-correction curve generally produces more accurate colour rendering. Fig. 3 shows the colour accuracy of the camera using the Hdnorm curve; each colour is shown as a blob where it should be and a cross where the camera produces it. There are significant saturation and hue errors, most significantly in skin tones.

The user should generally choose one of these two curves for working in HDTV, Hdnorm produces more vivid colouring while High is more accurate. For normal use, Knee can be set to Auto, but when the production will be going to a colour grading operation, Knee should be set either to Mid or Low, depending on the type of programme (Mid for programmes where skin tone is prevalent, Low for natural-history).

The other variants of the gamma curve were not investigated, the descriptions given in the manual

Figure 3, chromaticity of HDnorm curve

seem to be sufficiently accurate and explicit for the user to make an intelligent choice.

2.2

Resolution and Detail

The HVX200 is interesting in that the sensors are not native-sized for HDTV. The 3 ccds are each

960 by 540 pixels; it would be more usual to find sensors, in a 1080-line camera, having 1080 lines rather than only 540. Panasonic chose to use these lower-resolution sensors in order to increase sensitivity (since the pixels are bigger, the same 5µm square dimension as is found in ⅔” format

HDTV cameras. The camera delivers HDTV resolutions by physically offsetting the G sensor from

R and B by a half-pixel both horizontally and vertically. It is normal to offset just horizontally, when the delivered horizontal resolution is apparently about 50% higher than would be dictated by the pixel count alone. This quincunx offset increases both horizontal and vertical resolution, just how well can only be judged by measurement. This particularly relevant since the camera delivers signals at 1080, 720 and SDTV (both 576 and 480 lines in the two variants).

A zone plate test chart was used, calibrated for 1920x1080 HDTV. It contains 6 identical circular patterns, each being a phase space of the spatial-frequencies which such a camera should resolve.

Analysis was made of one zone to investigate the frequency responses and the presence of aliases.

2.2.1

Detail enhancement

However, a broad pulse (also on the zone plate test chart) was used for establishing reasonable detail settings, since the function of the detail enhancement is to sharpen edges rather than establish flat frequency responses. Fig.4 shows the effect of setting Detail Level to 0 and –2, there was no setting at which the overshoots were absent, and insufficient other controls to alter the

8

Figure 4, 1080-line pulse response

way the enhancement works. Judging by eye, setting level –2 seemed reasonable.

2.2.2

Resolution (1080-line)

Fig.5 shows a quarter of one circular zone plate, with zerofrequency at bottom left. The right-hand extreme is 1920 lines/picture width, the top extreme is 1080 lines/picture height. The alias patterns are clear, and indicate that the camera does not deliver full resolution at 1080, either horizontally or vertically. However, it is reasonably well behaved, in that there do not appear to be significant aliases centred on other frequencies, as would be expected if the interpolation process from the 960x540 of the ccds were compromised in any way. The precision-offset of the sensors in cameras is normally only horizontal, which delivers approximately 50% more horizontal resolution than the pixel-count, but with sensors in quincunx arrangement both horizontal and vertical resolutions are increased, but how well and by how much is debatable.

The strength of the existing aliases mean that it is difficult to measure the frequency responses accurately, since the higher frequencies are mixed with aliases. Nevertheless, it was possible to extract sufficient data using a software analysis program, to derive both horizontal and vertical frequency responses, and these reveal some interesting information.

Figs.6 and 7 show the horizontal and vertical responses for

1080i/25p (usually known as 1080psf/25, film style). It is difficult to decide how to present the amplitudes at greater than

960 horizontal and 540 vertical. It is clear that aliases

(unwanted) are present, but so is content at baseband

(wanted) frequencies. Since the recording format has a horizontal limit of 1440, not 1920, horizontal frequency content above 1440 must be only alias, there can be no baseband content.

In both figures, the green curve shows the response when both Detail Level and Vertical Detail are set to 0, the default value. Clearly, the designers have realised that it is more dangerous to have excess vertical detail over horizontal, but both curves seem excessively boosted at low/mid frequencies; it is in these low/mid frequencies that detail must be well controlled in order to generate a decent “film-look”, neither of these curves will do. To show how difficult it is to interpret the available measurements, Fig.8 shows the sequence of sample levels in a horizontal scan.

The settings given in Section 1 are not ideal; they are subjectively a reasonable compromise, but overall performance of the camera is not a good match to other

HDTV cameras in this respect.

Figure 5, quarter zone plate,

1080psf/25, detail=-2, v.detail=-4

Figure 6 and 7, horizontal and vertical responses, 1080psf

Figure 8, horizontal waveform

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2.2.3

Resolution (576-line)

Again, interpretation of data is difficult, but the subjective appearance of resolution is reasonable.

Fig.9 shows the horizontal frequency response. The bandwidth is well filled to the 720-pixel limit

(perhaps too well filled), but there are significant aliases between 720 and 1440, and the frequencies between 1440 and 1920 show strongly because they are twice-folded.

Evidently the Detail controls apply only detailboosting (some HDTV cameras have detail controls that allow detail reduction as well as boosting). For

SDTV use boosting is largely unnecessary, so a very low setting is reasonable, in Fig.9 the Detail setting level is 0, and is clearly too much. Judging by eye, a setting level of –2 is the maximum that should be used, and –4 looks better although the picture then starts to look soft because the boosting is done at too

Figure 9, horizontal response

low a frequency even in the Thin setting. The settings in the table produce pictures that look sharp at the expense of some visible boundary enhancement.

The same does not hold for the vertical response,

Fig.10, the response falls nicely to zero between 288 and 576, resulting in a moderate amount of interline twitter. The complete lack of vertical aliases at higher frequencies is good evidence that the camera can be used to shoot SDTV pictures, provided Detail is set sufficiently low.

Figure 10, vertical response

2.2.4

Resolution (720-line)

At the time of testing, it was not possible to analyse single frames of P2 recording, however the visual appearance was a good intermediate between 1080 and 576. The Detail settings in the table are visually appropriate for film- and sport-style shooting, where the film version uses minimal boosting although there is no setting that gets satisfactorily close to a real film-look. The sport version is appropriate for news, sports, any genre other than film-look.

2.3

Noise

No calibrated noise meter was available during the measurement procedure, and the camera specification does not mention noise. Again, software analysis of frames gives some indication of performance. Measuring the signal-to-noise ratio is just one colour patch of the Macbeth chart (the white patch when slightly under-exposed, 0db Gain) gives a figure of 44dB. Although it is highly dangerous to use such a small number of samples for analysis, the error is known to be less than

2dB, thus noise is between 42dB and 46dB. This agrees with subjective evaluation, and explains the high value set for Detail Coring. At +12dB, the noise is plainly visible; even with Detail

Coring

set to +4, the noise level was sufficiently high to cause detail enhancement to switch off, resulting in visibly softened pictures. This explains the Gain settings of +3dB and +6dB.

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