Question for Alan Roberts on HD LCD's

13 replies [Last post]
Mick jenner
Offline
Joined: Dec 8 2000

Hi Alan,

Could you have a look at this Dell TVhttp://www1.euro.dell.com/content/products/productdetails.aspx/lcd_w3202mc?c=uk&cs=ukdhs1&l=en&s=dhs

I want to know if it is suitable to get good quaility playback direct from the Z1 and how well it compares with other HD LCD's.

I am looking at it as a replacemnt main family Tv and also maybe to demonstate HD.

Many thanks in advance

Mick

Alan Roberts
Alan Roberts's picture
Offline
Joined: May 3 1999

Resolution's 1366x768. HDTV's 1920x1080 or 1280x720, so horizontally it's almost up to the FX1/Z1, but's fine vertically (since the FX1/Z1 delivers vertical resolution only up to about 720, same as for the 720p variant). When Sky start transmitting HD, they'll be sending a mixture of the standards, but on this display you won't notice much difference between 1080 and 720. Given that the viewing distance has to be about 3x pic height for optimal experience of HD, you'll be a bit close, so the actual viewing distance (probably around 5xpic height) will offset that.

So, as a domestic tv set, it looks fine; as a display for showing off HD, it's a bit marginal, you'd need something bigger and with more pixels.

Hope that helps.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

Mick jenner
Offline
Joined: Dec 8 2000

Many thans for that Alan.

I expect this might put you on the spot, but do you have any recomendations as to a 32in lcd TV.

reagards

Mick

Alan Roberts
Alan Roberts's picture
Offline
Joined: May 3 1999

That's ok, but I reckon it's about as good as it needs to be. The problem comes only mwhen you start to use displays in ways they aren't designed for. Domestic viewing is generally from around 3.5 metres (surveys have established this), and the acuity limit of the himan eye is generally accepted to be 1 minute of arc (1/60 degree, my limit is 0.7 minute). So you can now work out how far away tghe display has to be before the pixels just merge (i.e. when the pixel size is the same as your acuity limit). The maths is easy:

Because the angle is always going to be small, we can use simplifications.

We need to find the angle that an item of size S subtends at the eye distance D, COS(angle)=S/D, so angle=ARCCOS(S/D), and if we work in radians instaed of degrees, that becomes angle=S/D. Now S is the size of the pixel on the panel; in a 32" display the height is 32/SQRT(1+16/9)^2)=15.89 inches, so one pixel is 15.89/768=0.0204 inches high. Now we can see that if it subtends an angle of 1 minute of arc or more, 1 minute of arc is 2PI/360/60=0.000291 radians, so the distance at which it's just discernable is 0.0204/0.000291=70.22 inches, so if you watch this 32" panel from further away than 70 inches (say 6 feet), you won't see the pixels so it's fine. It's ,only mwhen you get closer that you can see them, and then the panel's structure gets in the way of the picture, so you need more pixel. Since typical viewing distance is around 3 metres (9.5 feet), it'll be fine for normal viewing, but if you want to show off the HDTV, you should be closer (at 3x pic height=3x15.89=47 inches, call it 4 feet, and at that distance, the pixels are too big, you can see them.

So, armed with all this, you can work out how many pixels the display needs to have for optimal viewing, you work out where you're going to view from, and the pixel count you need (limited by the 1920x1080 of HDTV), and the numbers will drop out of the eq1uations.

Hope that helps.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

Mick jenner
Offline
Joined: Dec 8 2000

Mant thanks again,

I knew I had ask the right man,

I now just need to inwardly digest your very comprehensive replies and a now make a well informed decision.

regards

Mick

Mick jenner
Offline
Joined: Dec 8 2000

Sorry to be a pest Alan but could you tell if the below is as good as the Dell ignoring the demonstration aspect just home use and in particular connected direct to the Z1 or HVR-M1

http://www.comparestoreprices.co.uk/lcd-tvs/sony-kdls32a12.asp

Many thanks

Mick

Alan Roberts
Alan Roberts's picture
Offline
Joined: May 3 1999

Yep, that's exacty the same resolution. Both these are fine for domestic viewing where you're not going to get too critical by getting too close. No comment on contrast though, you really need a display to deliver about 1000:1 or you'll see the black level as a visible grey, the best HDTV crt I ever measured delivered 3000:1 and most domestic tv sets will (surprisingly, at least I was surprised) actually do around 1000:1.

Hope that helps.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

Mick jenner
Offline
Joined: Dec 8 2000

Ta Alan, most helpful the Sony it is going to be.

Regards

Mick

JMCP
Offline
Joined: Nov 21 2000

Mick,

you sure about this telly, the specs are a bit confusing, HD Ready but it states in the specs
HDMI connection No
DVI connection No
HDCP enabled No

Is it possible it is only HD Ready as it can take a component input ?

Cheers John

Mick jenner
Offline
Joined: Dec 8 2000
JMCP wrote:
Mick,

you sure about this telly, the specs are a bit confusing, HD Ready but it states in the specs
HDMI connection No
DVI connection No
HDCP enabled No

Is it possible it is only HD Ready as it can take a component input ?

Cheers John

Now you are worrying me. I will do some further checks

Mick jenner
Offline
Joined: Dec 8 2000

I have now done some further checks on the sony site and on their spec's definately states HD READY also lists a HDMI connector,no mention of DVI connector or if HDCP enabled.

JMCP
Offline
Joined: Nov 21 2000

Mick,

thats good, if it has an HDMI connection then I am sure it will have HDCP. The reason I posted is that the previous website you provided the link to, had contradictory information in it for the HDMI connection. Enjoy your new telly and hopefully you will give us a wee review of it once you've had it for a bit.

Cheers John

Alan Roberts
Alan Roberts's picture
Offline
Joined: May 3 1999

Thanks for that, I'd not looked at that part, but it's important if the display's going to be used for HDTV broadcast. Sky's first generation HD boxes will have component outputs, just to pacify all those who've already got panels without DVI or HDMI, but the second generation boxes (and I suspect they'll be the ones with hard drives etc, first generation I guess will be simple ones) will most definitely not have component outputs.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

Mick jenner
Offline
Joined: Dec 8 2000

Thanks everyone, its coming on Monday and I will update you all.

Regards and a happy New Year to you all

Mick