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Old Feb 16, 2009, 3:28 AM   #1
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Been discussing lately megapixels and the myth surrounding them when it comes to buying cameras. I soon wondered if the rules apply or change when it comes to video and camcorders. So the quesiont is: What do megapixels have to do with video?

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Old Feb 16, 2009, 11:59 AM   #2
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Well, it depends. In the case of a hybrid, they will still advertise the megapixels for the still-camera aspect of the device. And you are correct, most of it is marketing buzz. Not only are the number of megapixels by no means a way to tell the quality of the picture you will get, but many of the low end manufacturers continue to lie about their specs by giving the consumer "interpolated" numbers.

But I rarely see megapixels mentioned when it comes to actual video. Usually you will see a resolution listed such as VGA, D1, 720p, 1080p, etc.. those type of figures. And occasionaly on the really low end stuff you'll see them list in numbers like 640x480 or 320x240. And the really, really low end stuff often won't list anything at all and just let the consumer guess.

However, it is still worth pointing out that there are no guarantees that a camera boasting 720p will definately give you better quality than one that does VGA resolution. Depends on the sensor type, the light performance, the lens, type of zoom, frame rate, compression, and most importantly of all - what you are going to do with the camera.
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Old Feb 16, 2009, 5:11 PM   #3
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Good question, adabo.

Up until recently(before the HD era) video resolutions(standard def) would top around 720x540=345,600 pixels. As you can see video resolutions were(still is used) well below a megapixel and therefore the term megapĂ*xels were never used with calculating video resolutions. Now with HD video it's a different story. Well we still don't use the term megapixel defining HD video, eventhough full HD is 1920x1080=2,073,600 pixels=2.1 megapixels. The RED ONE camera has an amazing video resolution of 4520x2540=11,480,800 pixels=11.5 megapixels. Maybe in the near future when we have higher high def resolution video, we will begin to use the term megapixels to define video resolution like still-photographs.
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Old Feb 17, 2009, 12:19 AM   #4
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Interesting reply's adric and adalfa. I was actually biased before posting. I didn't want to influence the thread with the first negative post. Having said that, I agree with both of you.

Side question: Why does my camera's specifications say "Image sensor 5 mega-pixel CMOS" and right under that "Still image 3MP, 5MP, 8MP"? I don't understand how you can get 8 out of 5.
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Old Feb 17, 2009, 9:48 AM   #5
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adabo wrote:
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Side question: Why does my camera's specifications say "Image sensor 5 mega-pixel CMOS" and right under that "Still image 3MP, 5MP, 8MP"? I don't understand how you can get 8 out of 5.
That's just a lame gimmick:G. Quite many of low cost hybrid cameras of today are based on a 5MP CMOS sensor. Ambarella and Micro are making newer generation chips but still not used yet. So we are stuck with the 5MP for now. Now 5MP isn't much compared to say a 14.7MP compact digicam and many regular consumers only look at how much MP a camera has and not chip size, image quality etc. So in order to "attract" consumers, low cost manufacturers use "interpolation" to increase image size. Like you would upsize/interpolate an image in Photoshop, here it's done with software in the camera. I'm thinking what a low cost hybrid camera engineer would say: "Why put in an 8MP CMOS sensor, when it's waay cheaper to just interpolate image size":G. I've seen low cost hybrids with a 5MP CMOS sensor which has image sizes up to 16MP:blahinterpolated of course).
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Old Feb 17, 2009, 10:34 AM   #6
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Loopholes! I'm amazed, and disappointed at the same time. :?
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Old Mar 7, 2009, 9:36 AM   #7
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Having an number of pixels that evenly divides into video pixels is also good, and stops you losing resolution. However, having an uneven number of pixels helps reduce fly screening effect of flashing pixels from the gaps in between them (the overlapping pixel falling in between them), but to preserve resolution I would recommend at least two pixels + uneven for every video pixels (minimising the resolution loss from the uneven pixel).

The other issue is that the different resolutions are different sizes and have some divisions in common (often requiring higher res to match in with each video resolution). So, 1080p and 720p have 2160p in common (8mp SHD). But the higher the resolution the smaller your pixel pad for a given sensor size, and the lower your latitude and worse the noise in low light etc. There is sensor technology where this is not a concern, but as far as I know Samsung has the license for that, but is not used in camcorders. As far as it is, I would avoid HD sensors of less than 1/2.5 until the technology comes through (1/3 maybe acceptable).

There are other issues in interpolation, cheap sensors may use a complimentary color mask, rather then the Mosaic or newer better masks, leading to color problems. Poorly illuminated sub pixels can introduce noise and error into pixels color. Many sensors perform down interpolation to video in sensor, and the cheap ones introduce errors by doing it wrong, as we have seen over the years with jagged details in pictures where instead of interpolating a slanted edge/line the edge travels in odd patterns. There may also be other concerns with interpolation errors, I can't remember.

So mega pixels are important for video too.

Sensors 2560 pixels across (like many of them) are probably not optimal for 1080p unless they crop it to 1920. At least 3840 pixels across is probably more optimal for video and stills.
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