PDA

View Full Version : pixels vs. zoom help



GaryPSU
09-25-2007, 11:38 AM
How much benefit do extra pixels provide when cropping with software? If I were to buy a 12 mp camera vs. 8 mp, how much would the extra pixels make up for a smaller optical zoom? Could I crop an image from a 12 mp 4x zoom camera and have the print look equivalent to an 8 mp that was taken at a 6X optical zoom? Thanks.

SpecialK
09-25-2007, 07:34 PM
"X zoom factor" is meaningless. "Focal length" is what is important. Some rough math...

8MP = 2320 x 3480 +/- pixels
12MP = 2840 x 4220 +/- pixels

So, you have 4220 - 3480 = 740 pixels in extra length of the image, or approximately 21% (740/3480).

So, without any enlargement or cropping, you can make a 10" print with the 8 MP camera, or a 12" print from the 12 MP camera.

Bynx
09-25-2007, 08:54 PM
I have a 7.1 megapixel camera. It produces each picture 42 inches by 32 inches at 72 dpi. So to get to 300 dpi for printing you have to reduce the 42 x 32. Is this the same with other lower or higher pixel cameras? Does a 4 megapixel camera output a smaller set size at 72 dpi? In effect you cant make as good a quality of enlargement. Does a 12 megapixel camera produce a larger size at 72 dpi and allows a larger enlargement than a 7 megapixel? In essence the larger the megapixel camera the larger the enlargement at 300 dpi.

GaryPSU
09-26-2007, 04:26 AM
"X zoom factor" is meaningless. "Focal length" is what is important. Some rough math...

8MP = 2320 x 3480 +/- pixels
12MP = 2840 x 4220 +/- pixels

So, you have 4220 - 3480 = 740 pixels in extra length of the image, or approximately 21% (740/3480).

So, without any enlargement or cropping, you can make a 10" print with the 8 MP camera, or a 12" print from the 12 MP camera.

I think that I understand what you are saying. It's not the just size of the print that concerns me. Basically, what I want to know is: If, using software, I crop the center of a 4220 x 2840 image to 3480 x 2320, isn't that equivalent to having had more zoom, but fewer megapixels, when the picture was taken? If so, how much more zoom. I'm trying to weigh the benefit of four extra mp.

David Metsky
09-26-2007, 08:04 AM
I think that I understand what you are saying. It's not the just size of the print that concerns me. Basically, what I want to know is: If, using software, I crop the center of a 4220 x 2840 image to 3480 x 2320, isn't that equivalent to having had more zoom, but fewer megapixels, when the picture was taken? If so, how much more zoom. I'm trying to weigh the benefit of four extra mp.
You can't just ask "how much more zoom" because things don't work like that. 3x zoom usually means something like a 35mm to 105mm lens, but not always. Once you have the image captured, zoom is meaningless.

In very general terms, moving from 8MP to 12MP gets you 21% larger image size, which on an average 4X zoom P&S might be the equivalent of a 5X zoom. It's not much, optical zoom will always beat out more MP. Plus, your 12MP camera is likely to be noisier then the 8MP one.

If you want zoom, buy zoom. MP are not a good substitute.

David Metsky
09-26-2007, 08:11 AM
I think that I understand what you are saying. It's not the just size of the print that concerns me. Basically, what I want to know is: If, using software, I crop the center of a 4220 x 2840 image to 3480 x 2320, isn't that equivalent to having had more zoom, but fewer megapixels, when the picture was taken? If so, how much more zoom. I'm trying to weigh the benefit of four extra mp.

Pixels are important; ignore the DPI information for now. If you take a 12MP image and crop it to 3480x2320 you have an 8MP image. You do get the equivalent of 21% closer to the subject, but that's not very much in the grand scheme of things. You can't measure how much more zoom (4x, etc) unless you know the specifics of the camera and what focal length was used. But the important thing to take away is that it isn't much. As I said in the other post, if you want zoom, buy zoom.

GaryPSU
09-26-2007, 11:19 AM
Pixels are important; ignore the DPI information for now. If you take a 12MP image and crop it to 3480x2320 you have an 8MP image. You do get the equivalent of 21% closer to the subject, but that's not very much in the grand scheme of things. You can't measure how much more zoom (4x, etc) unless you know the specifics of the camera and what focal length was used. But the important thing to take away is that it isn't much. As I said in the other post, if you want zoom, buy zoom.

Thanks for the reply, David. I get it now. It appears that the "zoom benefit" is nominal when going from 8mp tp 12mp. The camera that I want to buy must fit in a pocket, so I'll have to trade zoom for size. I'm trying to decide between the Canon SD870is (which I've "handled") and the Canon 950is - which I haven't seen yet. I really like the 3" LCD on the 870. Any opinion on these two?

John_Reed
09-26-2007, 12:10 PM
I think that I understand what you are saying. It's not the just size of the print that concerns me. Basically, what I want to know is: If, using software, I crop the center of a 4220 x 2840 image to 3480 x 2320, isn't that equivalent to having had more zoom, but fewer megapixels, when the picture was taken? If so, how much more zoom. I'm trying to weigh the benefit of four extra mp.The "X" factor of the zoom isn't important, but the maximum effective focal length IS important. If your hypothetical "6X" camera reaches out to 200mm and your "3X" camera to 100mm effective, then let's see what you get for comparison.

Let's say you shoot an image at full zoom with the "lesser" MP camera, and there's an object that stretches from the left edge to the right edge, thus it's 3480 pixels wide, captured on your camera's 8MP sensor. Now, zoom the other camera out to its full zoom, 100mm, and shoot the same shot. Because of the difference in focal lengths, the second image will capture your distant object at only half the width (ratio of 100mm/200mm). So, instead of taking up 100% of 3480 pixels in the first camera, it's going to take up 1/2 of 4220 pixels in the second camera. So what came out 3480 pixels wide on the smaller sensor only comes out 2110 pixels wide on the larger sensor.

Like the man said, the bottom line is, optical zoom will always nose out more megapixels if you're trying to capture distant objects. If wideangle is your thing, and you zoom rarely, you'll be better off with the larger sensor (MP-count large anyway). But don't make the mistake of thinking you can make up for the lack of zoom just by cropping.

David Metsky
09-26-2007, 01:08 PM
I'm trying to decide between the Canon SD870is (which I've "handled") and the Canon 950is - which I haven't seen yet. I really like the 3" LCD on the 870. Any opinion on these two?
I just bought an SD800 because I wanted an optical viewfinder that the 870 lacks.

The 870 has a wide angle lens, going from 28 to 105. The 950 lens goes from 35 to 133mm. If you want zoom, why would you buy a camera who's main selling point is the wide angle lens? Not all 4x are the same, you have to look at the focal lengths.

-dave-

GaryPSU
09-26-2007, 02:04 PM
I just bought an SD800 because I wanted an optical viewfinder that the 870 lacks.

The 870 has a wide angle lens, going from 28 to 105. The 950 lens goes from 35 to 133mm. If you want zoom, why would you buy a camera who's main selling point is the wide angle lens? Not all 4x are the same, you have to look at the focal lengths.

-dave-

I understand, and appreciate all of the responses. I have an old Olympus digital camera, and rarely, if ever, have used the optical viewfinder. I really like the large LCD on the 870, but I'll probably wait to see the 950 with its greater (133mm) zoom and 12mp. The specs show that the sensor is larger to accomodate the extra 4mp, so I assume that the image quality shouldn't suffer (noise). Speed between shots is not a factor, and SD memory is cheap, so the larger file size doesn't bother me either. Anything else that I should consider?

Razr
09-26-2007, 07:08 PM
How much benefit do extra pixels provide when cropping with software? If I were to buy a 12 mp camera vs. 8 mp, how much would the extra pixels make up for a smaller optical zoom? Could I crop an image from a 12 mp 4x zoom camera and have the print look equivalent to an 8 mp that was taken at a 6X optical zoom? Thanks.Look at the PANASONIC DMC-FZ50. It does precisely what you want to do, but it does it in the camera, not software

John_Reed
09-26-2007, 09:26 PM
Look at the PANASONIC DMC-FZ50. It does precisely what you want to do, but it does it in the camera, not softwareHe seemed to be asking the age-old question: "Gee, why can't I take a low-zoom 12MP camera and get the same results by cropping that I would get with a higher-zoom 8MP camera?"

The FZ50 does use a crop for its EZ modes, but they're all based on the same sensor, in fact at the wideangle end, minimum zoom, ALL lesser resolution EZ images take their pixels from the FULL 10MP sensor, which are appropriately downsampled after capture to create the required image size at the minimum focal length.