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Confusion over digital camera megapixels

by Lee Koo (ADMIN) CNET staff/forum admin / November 13, 2009 6:36 AM PST
Question:

Confusion over digital camera megapixels


Most manufacturers display the number of megapixels that their cameras have. What exactly is this number? Is it the number of pixels per square unit? If so what is this unit? In film cameras, the size on the film had a bearing on the quality of the final print, particularly enlargements and the larger formats were preferred by professionals who wanted to print large sized pictures. Is there an equivalence in digital cameras and do manufacturers display this? Under what name is this displayed? How much of this is good?

--Submitted by V.K. Subramanian

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Some answers --Submitted by kalel33
http://forums.cnet.com/5208-7593_102-0.html?messageID=3173999#3173999

Don't get sucked in the megapixel wars... --Submitted by stevehulk121
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Megapixel quality relates to sensor size --Submitted by muffindell
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Some answers

Megapixels are figured up by multiplying the horizontal resolution by the vertical resolution. This will give you the number of pixels in an image. Megapixels are one million pixels.

Sensor size doesn't have as much bearing on the final print, until you go really large and with a lot of megapixels. The larger the sensor, the shallower depth of field and the pixel density on the sensor is usually lower.

What you are able to print with what megapixel is not set in stone, but there are graphs that show what size of print you can make with different megapixels. Here's one for you.

http://www.lesjones.com/2008/07/15/megapixels-vs-print-size/

Now on the flip side, we have had quasi studies done to show that a 5MP and 13MP printed to 16x20 are indiscernible. Here was the article called, "Breaking the Myth of Megapixels".

http://www.nytimes.com/2007/02/08/technology/08pogue.html

Take the info how you like it, but for me, I don't need more than 8MP because I don't crop much at all.

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Size does NOT matter??
by MrGadgetman / November 14, 2009 9:29 AM PST
In reply to: Some answers

If I read your post right...

Sensor size doesn't have as much bearing on the final print, until you go really large and with a lot of megapixels. The larger the sensor, the shallower depth of field and the pixel density on the sensor is usually lower.

...then I am curious to know what you consider "really large with a lot of megapixels."? Because, from how I and the rest of us understand it, sensor size is important regardless of pixel count. The sensor size has about as much to do with depth of field as the memory card size. There are nothing but photo-quality advantages with a larger sensor. The only real drawbacks are expense, battery power consumption, manufacture, and camera body size ie weight. A 6MP D-SLR will take far better photos than say a 10 MP pocket thingie.

There is a reason why they put the bigger sensors in the bigger cameras. Other wise, what would be the point if it was all of no consequence.
The principles that effect a good photo are simple:
1. The more light through the lens, the better; aperture/lens size.
2. The larger the light capturing medium, the better; film or sensor
3. Composition; Exposure? Flash? Focus? Shutter speed?

Assuming you get the composition part spot on, you cannot deny the physics of it. You cannot refract down light but so much to fit on a small sensor without inheriting noise. More pixels on a sensor just means smaller pixels if the sensor surface area does not increase. So a small sensor and smaller photo receptors that fit on the small sensor to accomodate a high megapixel count does not equal quality to me. Sure, the picture will look fine on the camera's LCD or maybe even a thumbnail but when its time to print that bad boy..., all print sizes being equal the larger sensor will look better.

A larger sensor captures more light, so there is less noise because the software does not have to interpolate what didn't land on the sensor. This is valuable when it comes to photo editing like enhancemments to remove scars or blimishes, or when air brushing, etc. The less noise you start with the less you'll have at the end of the production.

Just my opinion though.

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Size does NOT matter???
by kalel33-20416052469708587370302374692233 / November 14, 2009 10:12 AM PST
In reply to: Size does NOT matter??

You read my posting right, but the original question had nothing to do with depth of field or high ISO/low noise. You made an argument about something that was never asked. I'd put up a Canon G11 print against many DSLRs at 10MP when printed at A4 size.

I shoot with a 30D and know the advantages of a larger sensor for DOF and high ISO, but that's not what this thread was about. It's about megapixels and print output. And, I did add in the DOF and pixel density of the larger sensors when I wrote it. I've printed 8x10s with my old Canon G2 that matched the quality of my 30D shots printed at 8x10, and that's a 4MP point and shoot compared to a 8MP DSLR. If were talking above A4 size prints then I would say a high MP Medium format camera is the best choice....but do you have $30,000?

Read the original question again and you'll understand my answer.

S

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Hmmm, I guess so.
by MrGadgetman / November 14, 2009 12:34 PM PST

Well, I guess I am confused then. You say I am arguing something that wasn't asked? Perhaps, but I could have sworn that you brought it up in the first place. It was your post that mentioned depth of field and noise, in relation to sensor size..., or I was responding to the wrong post? Did I copy and paste someone else's statement?

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You quoted me right
by kalel33-20416052469708587370302374692233 / November 14, 2009 1:00 PM PST
In reply to: Hmmm, I guess so.

but, I just added the DOF and pixel density as the reason why people choose large sensors, not because of making large prints.

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Depth of Field
by 9notes / November 20, 2009 11:01 AM PST
In reply to: You quoted me right

Just a side note folks. You've started talking about Depth of Field as a function of Sensor Size. Speaking as a professional Photographer in the days long before digital cameras were even dreamed of, I can tell you that the reason you get shallower DOF in cameras with larger sensors has far more to do with the lens than with the size of the sensor. One of you got part of it right when you mentioned that DSLRs with larger sensors had larger lenses with bigger apertures (allowing more light). Aperture opening is the primary determining factor in DOF. The larger the aperture (smaller f-stop) the shallower the depth of field. This is basic optical physics and has little or nothing to do with the size of the film or the size of the sensor. You can take that same DSLR with the big lens and shut down the aperture (think F-11 vs f-2.8) and you'll get dramatically increased DOF; again, regardless of the size of the sensor.

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Significance of Sensor Size
by Panmondiale / November 25, 2009 10:28 AM PST
In reply to: Depth of Field

First of all, thank you for explaining that Depth of Field (DOF) is a function of the lens, NOT the size of the sensor. Second, I'm surprised that no one has mentioned that pixel density is directly correlated to light sensitivity. In other words, the more densely packed the pixels are on the chip, the less sensitive it is to light; this is why the sensors with the highest number of pixels are on larger chips - the larger chip reduces pixel density, which improves light sensitivity (especially valuable in low-light situations, where the camera must activate it's on-board gain stage in order to boost the brightness of the image). The problem with gain stages, of course, is that they all have their own characteristic noise signature, which results in a "grainier" picture (but it's not grain as with film, it's noise!). In my experience, for most casual users a 5 - 7 MP pickup is plenty of resolution; I would offer the advice that a camera that is easy to use and has a good lens is a better value than a more expensive camera with more pixels that is either difficult to operate and/or has a mediocre lens. I sold Canon cameras for years, and I think that the price/performance value is among the best you can find. I also think they are one of the most intuitive cameras to use. I still use my Leica for "real" photography, but love my little Digital Elph for point-and-shoot snapshots of friends and family (and the occasional "art" shot when I'm not packing my Leica, 'cause the Canon will fit in my pocket and it's always with me and ready to go - hauling the Leica around like I do the Canon would be impossible!).

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G-man, you're right
by qprize / November 20, 2009 9:56 AM PST
In reply to: Size does NOT matter??

Ignore the rationalizations that follow. Size of sensor - especially in relation to pixels, is ULTRA important. For most people the larger pixels on a smaller sensor have become DETRIMENTAL to photos. On the standard "DX" sized sensor they've crowded too many pixels into too small a space. This creates electronic nois, (a sort of bleeding from pixels being too close, and it slows down the camera because it takes longer to assess and correct the image, and makes grainier pictures because more pixels need more light in the same conditions. Basically, for most people, who don't make 20" blowups, anything more than 6Mp is actually worse than 6, even on DSLRs and may even be worse than less than 6.

Good call Mrgadgetman.

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I think that's being questioned now
by kalel33-20416052469708587370302374692233 / November 20, 2009 10:13 AM PST
In reply to: G-man, you're right

The Canon 7D is now being considered the crop sensor high ISO/low noise champion, and it has more megapixels than any other crop sensor in history. It definitely makes a difference in small sensors, but DSLR sensors are able to do pixel binning and sharing information between pixels to get farther.

It's not as simple anymore of more MP will equate to grainy photos. I think we have hit and surpassed the MP limit in compact cameras, and now were seeing some cameras go backwards.

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This needs some correction
by hjfok / November 20, 2009 10:29 AM PST
In reply to: G-man, you're right

"Basically, for most people, who don't make 20" blowups, anything more than 6Mp is actually worse than 6, even on DSLRs and may even be worse than less than 6."

Actually if they don't blow up the photo, they will not likely see the noise. It is perhaps more appropriate to say that for people who don't make large blowups, they wasted their money to pay for the extra pixels. Sensor technology is pushing the max limit of pixel density. Obviously if one routinely makes large prints, one should get a bigger sensor camera with more pixel counts rather than a small compact with more pixel counts.

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Pixels
by gandhawk / November 20, 2009 11:46 PM PST

A 6 megapixel camera will take nice photos and you can blow them up to 8X10 with no loss of picture quality. The reson I like the 10 or larger megapixel is that I rare print a photo without croping. If you crop 20% of the photo taken on a 6 megapixel camera and and blow it up to 8X10 you will notice some loss of picture quality. That is why I go for the larger megapixel camera. I am not a professional photographer and do not know about noise and DOP issues that are discussed.

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Better To Use a Lower Pixel Camera for Internet Pictures
by jrj90620 / November 20, 2009 10:54 AM PST
In reply to: G-man, you're right

I found out that when my old Canon A60 2meg pixel camera failed and I went out and bought a highly touted Canon A590 8meg pixel that I could never get as good a picture when using to make pictures for Ebay postings.I don't need large size for internet postings.I got the A60 repaired and sold the A590 on Ebay.It seems that when Canon went from 2meg to 8 meg that they end up packing a lot more pixels on the same size sensor resulting in each pixel sensor being much smaller and therefore less light is picked up,resulting in a lot more noise in pictures.I'm keeping my great A60 for Ebay.

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Got that beat!...
by DerfX / November 20, 2009 8:06 PM PST

...Just kidding Wink But I have a weird one. I have this old Sony Cyber-shot 3.2MP that's works just incredible. Big downside, it's so old, it can't use today's mega-sized memory sticks. It's stuck with it's old original default size and you can only get about 80, (+/-10), fully high resolution max size/quality shots saved on each stick. And finding those sticks is becomming more difficult. Fortuntely, I have a couple so I can still go crazy when I'm on vacation and every one of them can be blown up to a beautiful 8X10.

It connects to the PC via the old original USB which isn't that fast, takes almost a minute to download a couple dozen pictures. The darn thing had so many negative reviews that I don't think they sold that many. But if you get your hands on a good one, you'll never need anything else!

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Resolution in terms of sensor pixels per square unit
by archeoptimist / November 21, 2009 10:16 AM PST
In reply to: Size does NOT matter??

160 years ago, a "camera" was a room with a pin-hole sized opening to the outside. (Try it.) If a light-sensitive surface is exposed to light coming through an opening),there is a complicated, but manageable, mathematical relationship between the size of the opening and the area of the sensing surface that determines how "sharp" a recorded image will be. For photographers who worked 160 years ago, the materials that reacted to exposure to light were not very sensitive. As a result, cameras had to be really big, and pictures of moving subjects could not be made. "Hold still and say "Cheese"." But for ultimate sensitivity and image sharpness, the lens would be as large as practical and the sensor surface would have the largest number of pixels in the smallest possible area.

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good answer
by Jephy / November 21, 2009 11:07 PM PST
In reply to: Size does NOT matter??

Helpful info from an enthusiast--or possible expert--who clearly understands the subject AND has communication skills! Unheard of!

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Typical Internet Experts
by bobh2009 / November 23, 2009 3:19 AM PST
In reply to: good answer

As usual the "experts" have grabbed the ball of irrelevance and run with it.

A person asks a relatively simple question and a few egomaniacs turn it into an argument about who knows the most about what wasn't asked.

It's a shame that a handful of people with nobody to talk to in real life have to dominate these rooms with their garbage attitudes.

Nuf, said. Thanks for ruining these sites.

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sensor size
by chuckkski / November 24, 2009 7:44 AM PST
In reply to: good answer

How does one find out the sensor size of a given digital camera when shopping??

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Using pictures on data projector
by stanley Armes / November 20, 2009 1:32 PM PST
In reply to: Some answers

I have a 5 pixel camera but the problem is that when I use the pics on a data projector it gets digitalized. So a higher pixel will solve the problem. I use the pics in Power Points etc. Thanks

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Print size
by stanley Armes / November 20, 2009 1:55 PM PST
In reply to: Some answers

Thanks for the print size chart. Does this apply to projection on a wall/screen with a data projector?

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Megapixels
by pegpluscol / November 20, 2009 3:21 PM PST
In reply to: Some answers

I tend to agree with Kalel33 and others here. All have made good points. Although back in 1960 as an amateur I covered weddings, used models and did a little table top work, I'm still an idiot regarding digital cameras. As a rookie I believed that the more definition the better, until I began evaluating pictures of my models. The camera really brought out the pores and fine hairs, hence the change to soft photos. Perhaps the best way to describe the value of pixels is whether you want a poster, a picture on the wall, on the office desk or in the photo album. An oil painting looks like a 1kb camera when up against it, and beautiful at a distance. But us oldies have also consider our failing eyesight. This is why I changed from a small digital with a small LCD to a 12mp DSLR. I take snaps for my personal use mostly.

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Megapixels and the Marketing department . . . .
by tdidawg / November 21, 2009 1:17 AM PST
In reply to: Megapixels

Most people get caught up in the pixel wars pretty much started and continued on by the marketing folks at Canon and Sony. For the most part, for most people taking nothing more than snapshots of the family a camera with two or three megapixels work just fine. That's right, three megapixels. DON'T FORGET MEMORY! My guess the person that used their photo's in a PowerPoint presentation with their 5 MP camera, took the photos at a greatly reduced image size, and probably with a lot of compression!

Memory is really CHEAP today, so buy a large card(s), and use the very best quality (lowest compression)and all the pixels your camera has. If you're HD television is a 720P set, it may have less than 1 million pixels, and as such, can't display the full quality of your photos!

Key things to look for -
Glass - If you have a bad lens, not much else matters!
Sensor size - SLR or look for one of the new compact cameras now shipping with an APS - C or larger sensor if you can afford to do so.
Lots of Memory - with Highest and Largest size your camera will take ( especially important if you're not sure what you're going to do with the image.
Think before you shoot! - Fill the viewfinder with your subject - Cropping = Lower Resolution / Quality!

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Sensor Size
by fmreilly / November 21, 2009 4:34 AM PST

You recommend an APS - C or larger size. What sizes are larger? What are the scales?

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Sensor Size versus Depth of Field
by markdoiron / November 20, 2009 8:51 PM PST
In reply to: Some answers

Kalel33 wrote: "Sensor size doesn't have as much bearing on the final print, until you go really large and with a lot of megapixels. The larger the sensor, the shallower depth of field and the pixel density on the sensor is usually lower."

I just want to clarify that you're not writing about sensor size as measured in megapixels. You're writing about sensor size as measured in inches/millimeters/whatever. Though there is a relationship between physical size and megapixel size, that's not exactly what the original question was about. But, to further explain, the loss of depth of field when using a physically larger sensor (in inches, not megapixels) is because of the multiplication factor of lenses to accommodate for the different sensor size. If you want to take the same picture with two different size sensors, one a "full size", one requiring a 1.6x multiplication factor, then you'll need to use a longer focal length lens on the larger sensor. This longer lens is what causes the loss of depth of field.

Also, regarding larger megapixel sensors having more noise: It would be a mistake to try to compare camera noise levels based on their sensor size. There are a number of other factors that contribute to this. If camera noise is critical to the purchaser, better to compare test data directly and not try to use sensor size as a proxy it.

Finally: What most point and shoot snapshooters need to know about sensor size is bigger can be better--to a point. This is because most point and shoot snapshooters are terrible photographers. The single, biggest improvement that most can make to their work is to get closer. Since most have poor habits and shoot from too far away, better to have a too larger sensor, then to use cropping on the computer to make up for poor technique on the site (and, please be aware that a photo of an object taken with a telephoto (which is essentially what one does when they digitally crop in the camera [never do this!!!] or on the computer), and a photo of the same object taken by stepping closer to it are two entirely different pictures. Understanding this most basic fact of photography is one of a number of things that differentiates competent amateurs/professionals from the typical snapshooter.

--mark d.
http://www.summitpost.org/user_page.php?user_id=26307

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Why are good cameras expensive?
by archeoptimist / November 21, 2009 11:11 AM PST
In reply to: Some answers

There is a "tipping point" in photography where the "quality" of camera lenses and the "sensitivity" of film or sensors to record a picture, combine to create an image that equals what we see. Big, expensive lenses accept more light and focus it accurately on smaller, high density sensors to make accurate, "real life" images of what we see.

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Megapixel Math Question
by pruez / November 21, 2009 2:15 PM PST
In reply to: Some answers

Yes, if you multiply the horizontal x vertical number of pixels you get the megapixel number. How do you do the math in reverse? How do you get the horizontal x vertical number of pixels from say an 8 megapixel measurement?

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Reverse math
by LionsMike / November 22, 2009 1:07 AM PST

It would be nice to be able to say that it depends upon the length and width (or the aspect ratio). a 6:4 ratio would make the math simple 6x times 4x = number of pixels, however pixels are not necessarily square, and aspect ratio is not standard. Most cameras do work around 4" x 6" pictures to be compatible with the printer paper which is common. If you use that you should be reasonably close.

a 5 Megapixel photo at a 1:1.5 ratio (4 X 6) would be about 1800 X 2700 Pixels

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One correction
by Maaky / November 22, 2009 10:02 PM PST
In reply to: Some answers

The number of MP absolutely does not affect Depth of field!. Depth of field is controlled by the size of an image element, and F-Stop.

In addition, the depth of field is tied in closely with a phenomenon known as circles of confusion. Which is aptly named, but can be simplified by knowing that an image is critically sharp at only one focus point. And as teh image goes further or closer to the camera, it will go out of focus, and what would have been a point, is now a circle, which gets larger as the image moves away from the critical focus point.

The F Stop will tend to make these circles of confusion smaller *** the lens is stepped down, continuing to decrease in size. When the diffraction limit of the lens is reached, the image will start to display a general unsharpness. This usually happens around 1 f-stop from maximum, but varies by lens.

Megapixels do start to have less effect as they increase.

(I'm going to try this without math, or at least just simple math.

While a 2 megapixel image is a big increase over a 1 MP image, If we have say a 10 MP image versus a 12 MP image, there will hardly be any increase in quality at all.

If we're looking at 300 dpi images, that 12 MP image is only going to be around a 1/4 inch or so bigger - the exact number depends on the aspect ratio of the sensor.

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it's really about dpi
by halkelley / March 12, 2010 10:43 PM PST
In reply to: Some answers

Dots Per Inch in your "print" or whatever media the final image is displayed upon..."magazine quality" is generally accepted to be 300 dpi, so as long as your camera has enough pixels to cover that you are up to that standard...as many have already said, it's blowing up the image, or cropping and blowing up the cropped portion, that ultimately reduces the dpi in the displayed image, that makes many photos unacceptable...however, as also has been pointed out, lens and sensor quality effect the final image, but most cameras on the market have acceptable physical components

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megapixels
by bobc47 / November 13, 2009 9:00 AM PST

The megapixel quote is the total number of pixels the camera's sensor has. Compact cameras have very small sensors while digital SLR's have much larger sensors. In most cases, the larger the individual pixel, the lower the noise in the resultant image will be. Noise becomes more apparent when you blow up images

A 10 megapixel compact camera (with a very small sensor) can have a poorer resulting image than a 6 megapixel digital SLR with a much larger sensor, especially in low light.

You have to read the reviews carefully to get a camera that meets your needs.

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Sensitive cell phones, cheap lenses.
by archeoptimist / November 21, 2009 11:44 AM PST
In reply to: megapixels

You are right. A low-quality lens (a lens that does not accurately reproduce the image that is presented to it) that projects its collected light to a dense, sensitive sensor chip will store an unsatisfactory image. Unfortunately, a high-quality lens will project an accurate, high-quality image on a sensor that cannot properly record it. To the greater extent, we get what we pay for. If we will accept a fuzzy image under any light conditions, we probably will be happy with a cell phone image on a high pixel-count sensor.

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