Pixel count & image dimension - are they proportional?

Papaji

Wanted to ask that if an 8.1MP digital camera captures images in the following 5 dimensions:

(1) 3264 x 2448 (2) 2592 x 1944
(3) 2048 x 1536 (4) 1600 x 1200
(5) 640 x 480....

...is it that only the largest image (3264 x 2448 dimensional image in this case) an 8.1MP file? Are the smaller dimension images such as the 1600 x 1200 or 640 x 480 lower on pixel count?

I ask this as I am wanting to upgrade from a 3MP cam to an 8MP one.. but since most of the images I store on my hard-disk, I resize first to a decent 1600 x 1200 size... which could mean - for what I am suspecting here - that I am, in doing so,reducing the pixel-count as well..

I'm not sure if am being able to get my query across.. so here's another way that I'll attempt to ask it..

..there's an image that has been captured by a 10MP plus DSLR and there's another image that has been captured by a 4MP point-n-shoot digi-cam... now if we downsize both pics to say 600 x 400.. does their Pixel-count then drop to the same level?

I'm confused, plz help!

Yogesh Sarkar

In a nutshell, Yes!

That is why one should always look at the quality of the image produced by a camera, rather than relying upon pixel count to make purchase decisions.

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Papaji

..no but if I take an image from a 10MP DSLR and reduce it to a 600 x 400 pixel-size image, for display purposes.. a lot of the original data in the form of pixels is lost, i suppose, for a 600x400 sized image cannot contain all of the 10 mega-pixels.. My question is - which pixels go..? and which remain..? or is it that 4 pixels gets compressed to take up space equavalent to 1 pixel on the screen..this though seems to be the least likely..

somebody plz explain!

mairangi_vice

Hi Papaji,

For your original question, the dimensions of the image ie 600x400 are in pixels, so this image would have 600*400=240,000 pixels, and so on. The MP rating of the camera is the biggest photo that can be taken

The second question is a bit more complicated, and the exact answer depends on what software you are using to edit the images.
When you scale an image down the software groups the pixels together, the size of the group depending on the level of scale change you want. Then the pixels are either averaged (or some other similar statistical approach) to find a representative colour value, or some pixel itself is chosen to be representative (eg the center one in the grouping). A pixel with this chosen colour value is then added in place of the group.

Hope this helps.

Papaji

..going by this, one shouldn't go in for an camera-upgrade just for an increased mega-pixel count.. if one intends to set the camera to shoot in small-size.. or, if one is going to downsize the images shot in bigger sizes..right?

..another thing.. is the pixel size constant.. or can a pixel be compressed or blown up to occupy less or more dimensional-space respectively?

..wikipedia says that it variates (or maybe I'm unable to read it correctly) depending upon the resolution that's set on the monitor..

Screen Res: 1024x768, Diagonal Size: 19", Pixel size: 0.377mm
Screen Res: 800x600, Diagonal Size: 17", Pixel size: 0.4318mm
Screen Res: 640x480, Diagonal Size: 15", Pixel size: 0.4763mm

..now had they- in the above 3 observations- kept one of the factors constant (either the screen res. of the diagonal size.) it would have been easier for me to grasp ..as of now, I need someone to explain it to me..

Hi Yogesh,

what defines picture quality? my question to you

One, the size of the sensor, I've read...
..lenses, another..

..a Canon S5 IS, is what I was thinking of buying. I presently use a Kodak 3.1MP... do I even need an upgrade..?

man, u've gotta guide me

Yogesh Sarkar

Size, quality and sensitivity of the sensor, optics i.e. lenses, amount and quality of post processing done in camera, color space used and a lot more. I don’t think I am qualified/experienced enough to be speaking on this subject, but here is an interesting article that I recommend to all my friends who believe expensive cameras take better photographs, http://www.kenrockwell.com/tech/notcamera.htm

Edit: here is another article that you might find interesting, The Megapixel Myth

mairangi_vice

Right.

The image can be displayed in any number of ways on your computer. If you have an image that is 600x400 and your computer monitor has a resolution of 600x400 also, then 1 image pixel= 1 pixel on your monitor. If your monitor had 1200x800, and the image was displayed full screen, then each image pixel would be displayed using 4 pixels (2x2) of your monitor.

If you stacked up 240,000 monitors 600 wide and 400 high, and displayed your image, then each individual monitor would act as 1 pixel, and display 1 colour. Of course you would have to stand a long way away to view it.

Papaji

Yogesh - thanks..I'll read the links, but I take time to read..so this'll have to wait..

right now, over to Vice

Vice - things have started to make sense..or atleast I'm now turning hopeful

Q: Is there absolutely no variation, whether of colour or shade, within a pixel?

Q: So, as per you, the size of a pixel is defined.. when we blow-up or reduce a pic, the number of pixels get multiplied or divided to resize the image according to display; the size of individual pixels remains unaffected. Right?

Q: Any good point & shoot camera that you could recommend for me?
Actually the 3.1 MP camera isn't totally mine I have to share it with everyone in the family..and there've been times when I have had to make-do without it.. anything you could recommend?

mairangi_vice

Thats right, 1 pixel = 1 colour.

On your computer monitor, the screen is made of a certain number of pixels. Each one is effectively a tiny, multi-coloured light, if you look at your screen with a magnifying glass you can see them. This is 1 pixel on your screen. Obviously the physical size of these 'lights' cant change, so the screen pixel size is fixed. But several of these 'lights' can light up to represent a single picture pixel. Resizing, zooming and displaying all affect how the screen displays the image.

I think though that you would do well to ignore everything that has been said above. If all you want is a camera to take some pictures and share them with your family, then almost any camera with more than 3MP will be fine. All major camera makers have been making digital cameras for years now, and they are mass produced and of generically high quality. Unless you want to go into professional type photography, it really doesnt matter as long as you buy from a reputable brand - Sony, Canon, etc.

My last camera was a 3MP Sony cybershot and it was fine, until someone got it wet. So my new camera was purchased solely because it is water resistant, I didnt even bother with technical specs because they are all the same.

Nick-H

I have two five-megapixel cameras.

One is in a mobile phone (I wanted to have a camera in my pocket all the time, so bought the first expensive phone I've everb had), and the other is my Cannon S2 IS.

Whereas the phone camera takes pretty good pictures, compared to many that I've seen from phones, it's quality is now-where near that of the Cannon.

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Papaji

thanks very many to all 3 of u but before I go... Why does a 600x400 pic taken by a 6MP camera appear to be sharper in contrast to a 600x400 pic taken by a 3MP camera.. I mean, are we absolutely sure that both pics have 600*400=240000pixels(.24MP)???

also, there is a setting on some digi-cams which lets us select between an ultra fine, a fine or a normal quality of image to be shot.. now, how could that work, if the pixel size is to remain static? plz

mairangi_vice

The pic from the 6MP camera might have better contrast because as the pixels are averaged when the image is resized, the larger pic will have more values to average giving a better representaion.

The different quality settings are to do with how the camera encodes the image. A low quality image will use less information per pixel, but will take up less space in your camera memory.

Yogesh Sarkar

Maybe because the sensor, optics and software of the 6mp cam are better than that of the 3mp cam. If you were to compare photographs of the 6mp D40 (dslr) with a 10mp consumer cam, you will notice that d40’s photograph is much sharper because d40 manages to capture details much more precisely.

Because majority of the cameras store photographs in jpg format, which is a lossy compression method i.e. information is lost when you compress the raw image but size is reduced significantly. Usually less compression you use, the better and sharper the photographs would be.

Papaji

this makes sense.. so if I use a more refined camera to take smaller-dimensioned images (roughly 3MPd) they'd be sharper looking than what comes out of my fairly old 3MP point-n-shoot.. that answers me thanks


..I get it..so that is why if we change to the fine or ultra fine mode, lesser number of images (of the same pixel-count) can be saved to the memory card.

You've been of help