Confused over Megapixels.

[shaduf]

I have a Panasonic FZ5 which is nominally 5Mps.
However, when I set it to Widescreen Mode or HDTV as they call it, it drops to 2 Mps.

I also own a Panasonic FX8 (which my wife uses) and that is a 5Mp camera but that drops to 3.5Mp or 2Mp depending on which picture size I go for when I want to do 16:9 Widescreen.

Having taken pictures for years at a ratio of 4:3 I think it is now time to standardise on widescreen but I'm not happy about the drop in pixel count.

My next camera (very soon) will probably be the TZ3 and although that's a 7Mp camera it only drops to 6Mp when taking widescreen. That's much more acceptable but I can't help thinking I'm missing something?

Why is there such a drop on the earlier cameras?

Can you enlighten me please.

Shaduf

[Liquid101]

I suspect it has less to dowith aspect ratio, and more to do with native resolutions.

If you display a high resolution image on a TV with a lower native resolution it creates all kinds jaggy lines etc. caused by interlacing. Modern cameras probably output using progressive scan and can support higher resolutions without this effect.

This is based on my limited schoolboy knowledge of such things

[martin greaves]

I think that there are a number of different factors here.



First with the FZ5, the HDTV mode was probably designed to exactly match the resolution of a a 1080 hi-def TV, 1920*1080pixels=2MPs.



On later cameras the change in resolution between modes depends on the aspect ratio of the sensor. If you start from a standard 4:3 sensor and then convert to 16:9 you effectively lose 25% of the overall resolution (or ~12% going to 3:2). For example with a 5MPs 4:3 sensor the resolution is ~2580*1936pixels, this becomes ~2580*1452 for 16:9 or ~2580*1720 for 3:2 taken with the same sensor- the horizontal resolution of the sensor is the limit in both cases.

However if you start from a 3:2 sensor and then convert to 16:9 you effectively lose ~15% of the overall resolution (or ~12% going to 4:3). e.g. 3:2 5MPs sensor the standard resolution is ~2738*1825 - this becomes ~2738*1539 for 16:9 (limited by horizontal resolution) or ~2433*1825 for 4:3 (limited by horizontal resolution). Looking at the specs for the TZ3 the sensor seems close to 3:2 so the drop in resolution in going to 16:9 is ~15%

[shaduf]

Martin,
Thanks for your very detailed explanation. I'm not sure if I fully understand it but nothing seems to take away the fact that the new TZ3 takes widescreen pictures at a significantly greater resolution (6.0mp) than my older FZ5.
On that basis it should be a lot better.
The comparative picture sizes are 1920 x 1080 on the FZ5 and 3328 x 1872 on the TZ3.

Thanks again.
Shaduf

[martin greaves]

An easier way to think of it is to think of you sensor as a TV.

If you have a 4:3 TV and show a 16:9 picture on it yet big black bars at the top and bottom of the picture. Conversely if you have a 16:9 TV and show a 4:3 paicture you get big black bars at the side of the picture.

On a camera these black bars are parts of your sensor that don't get used to take a picture, and this is where the megapixels are lost.

If you were to have a 3:2 TV (if one existed!) and show a 16:9 picture you would still get black bars at the top and bottom, but they would be smaller than showing a 16:9 picture on a 4:3 TV - this equates to losing less megapixels on a camera. You also however get black bars at the sides when showing a 4:3 image, this means megapixels are lost when taking a 4:3 picture.

Hope this makes sense.

[shaduf]

Yes thank you Martin.