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How many megapixels do you need?

In buying a digital camera, the first question one will run into is "how many megapixels" do I need? As this is the most visible advertised feature in digital cameras these days, it's important to understand what you truly need.

How large do you want to print your photos?

When it comes down to it, deciding on the resolution for your digital camera is as simple as determining what you would like to do with the printing. If all you want to do is capture basic snapshots that are intended to print as a 4" x 6" (4x6) photo, then it is possible to get away with even a 1.0 - 2.2 Megapixel (MP) camera, depending on the final output quality desired.

However, most of us like to be prepared for the fact that someday we may capture a photo that deserves "blowing up" / enlarging or even cropping. This is where high-resolution digital cameras come to shine.

Print Size Minimum Resolution
(200 DPI)
Best Resolution
(300 DPI)
4 x 6 inch 1.0 MP 2.2 MP +
5 x 7 inch 1.4 MP 3.2 MP +
8 x 10 inch 3.2 MP 7.2 MP +
11 x 14 inch 6.2 MP 13.9 MP +
13 x 17 inch 8.8 MP 20.0 MP +
20 x 30 inch 24.0 MP (*) 54.0 MP +

Important Notes:

  1. The above table indicates the achievable print sizes straight from the camera. Given the techniques shown on other pages (using Photoshop or IrfanView), one can achieve print sizes greater than what is shown above.
  2. The data in the above table is easy to calculate. One takes the print size and multiplies the two dimensions (in inches) to get the area in square inches. Multiplying the area by 0.04 for minimum resolution and 0.09 for best resolution will give the megapixel counts stated above.

    Where do those 0.04 and 0.09 come from? It is generally accepted that the minimum resolution in a print that is suitable for close viewing is about 200 DPI (dots per inch). So, for a one-inch square, we would need 200 dots x 200 dots = 40,000 dots = 0.04 megapixels. Similarly, the resolution at which the human eye would have a hard time "seeing the dots" is at or about 300 DPI, which corresponds to 300 x 300 = 90,000 dots or 0.09 megapixels.
  • NOTE *: With very large prints (eg. 20x30 inch prints), one can get away with much lower effective resolution (than say 200 DPI) because the viewer will often see the print from a distance. Therefore, the rule of thumb suggesting a 200 DPI minimum is not as realistic. It is possible to get reasonable prints at this size from 10 megapixel cameras, for example. One can also take advantage of some excellent image editing software packages that are able to interpolate (up-res or up-scale) "natural" images to much greater resolutions very effectively (e.g. Genuine Fractals).

Why do some Canon cameras set the resolution to 180 DPI?

For the longest time, I tried to figure out why the Canon 10d generated photos that were tagged with a resolution of 180 DPI. Why not 300? After giving it some more thought, it likely that they wanted the 6.0 megapixel camera to automatically imply a print size of 11 x 14 inches for advertising purposes (but notice that this requires a lower resolution than the 300 DPI that is standard for printing).


Reader's Comments:

Please leave your comments or suggestions below!
 For photos for my book, my publisher has to have 300dpi. I have photographed letters, old photographs, and newspaper photos as well as a few new scenes with my iphone46s which has 24 megapixels. Is this enough dpi?

The book is 5 X 8 so photos will probably be 4 x6 or 4x7.

 Hi Claire -- I believe your iPhone 6s provides 12 megapixels (not 24). From the publisher requirements, if you are targeting images up to 4"x7" at 300dpi, you would theoretically need: 1200pixels * 2100pixels = 2.5megapixels. Your iPhone's photos should be more than adequate from a resolution point of view.
 I have a canonpowershotS95 can I shoot high resolution 300DPI at 3"x2"?
 Hi Calvin: my editor wants 11 x 17" photos at 300 dpi. Will my Nickon Coolpix5400 which says "5.1 effective megapixels" deliver this and if so how do I set it for that? In the menu on Image Size, the largest is "5M" with the image size 2592 x 1944. What are these numbers? Confused as heck. Thanks a bunch!
 If your editor wants 11x17" at 300dpi, you theoretically need to produce a file that is 3300x5100 pixels, which corresponds to a total image resolution of just under 17 megapixels. Your camera only captures 5 megapixels so that means you'll need to "up-res" your image (eg. in Photoshop) to meet their image file request.

In Photoshop, you can perform the up-res process by opening your photo, selecting Image -> Image Size... and then entering in the width of 17 inches and Resolution of 300 pixels/inch. Make sure Constrain Proportions and Resample Image are enabled. Under Resample Image, you might want to select Bicubic Smoother. Resave as a new file.

Be forewarned that the up-res process doesn't create any new image detail and your camera is relatively low resolution (by today's standards). Therefore, the up-res result might not meet the standards of image quality that your editor is looking for.
 I am using a Sony NEX 7 camera. It usually shoots 350 dpi. It seemed to switch to 240. I need to have the 350 to print something large. How can I change it back?
 The best solution is usually to set the resolution inside the photo editing software that you are using to print the photo. Generally there is an option to select the output size and/or resolution. Note that most cameras don't let you change the default resolution that is stored inside the image files (metadata).
I have to take a picture of a tall building.
The print out will be 7meters high by 3 meters wide.
I have a pentax K7 14mp
The photos are 300dpi
But canvas size is only 0371.5mm I need at least 1.5m
What do I need to do to get a quality print

With thanks
 Well pictures come out clear with a 14.2 megapixel camera with a 75-300mm lens
 I have to take a portrait pic of very specific sizes. It's 600px x 600px and the distance from the eyes has to be 336px X 414 px. I got canonPowerShot S80. How should I set up my camera and do I have to do the rest resizing by using Photoshop program? Thank you.
2011-07-02Aura Katigbak
 Hi! I have several queries about resizing up and cropping photos. I have a Panasonic Lumix DMC FZ7 which is a 6mp cam and it is set at 72dpi.
First question is: Is it possible to print the photos I took up to 20"x30"? if yes, how?

Some of my photos were taken using canon ixus 950is, which is an 8mp cam set at 300dpi. I have cropped some of them, decreasing their sizes at 6"x8". Now for other question: Is it still possible to produce a clear print up to 20"x30"? If it is not possible what is the maximum clear print that I can possible get? But if yes, again how?

 I am so stuck right now..I have a 10 mp camera..I have taken photos with the ratio at 16.9 and mp at 10 so now i am having a problem even printing to a 4 x 6 without it cuttng the edges off?? am i just doing something so wrong? I have PS elements 9 and have tried resizing the photo to a 4 x 6 and it still is cutting the photo down on the sides..I am so frustrated..a friend told me that my photos are to long and narrow? Help i am at my end on this and about to give up? hope you can understand what i am talking about its been a long and non eventful day. Thanks
 Hello Retta -- if you were taking the photos in 16:9 mode, then the "aspect ratio" (ratio of width to height) will not match the shape of 4x6" prints. You only have two real options: 1) use the full width of your original photo but print white borders at the top and bottom of your image ("no crop" mode) or 2) use the full height of your original photo but crop the sides off your photo ("crop" mode). Unless you can cut down on the physical size of your prints from 4"x6" to ~3.375"x6" , the most common solution is to crop off the sides of the image. If the sides of your image are important, then I recommend resizing your image to 3.375"x6" instead. 16x9 mode is OK for taking photos destined for display on widescreen televisions and monitors, but otherwise it's best to keep it in 4:3 or 3:2 modes.
 How many mega pixels in the highest resolution image captured by a digital camera
 There are a few "prosumer" digital cameras today that are over 20 megapixels. There is even a panoramic camera (Seitz 6x17) that takes images with a resolution of 160 megapixels!
 Hi I am hoping you can shed some light on a problem that I have stumbled on. I am in the process of creating a book cover an author. I was just told today that I needed 300 dpi. They checked my images to find everything was 72 dpi.
Can these images be changed to 300 dpi somehow without losing quality of the image? I do have a camera that is 12 megapixals. I believe a 300 dpi needs a 7.2 mega pixal camera from what I have figured is this right. So does that mean if I take images with this 12 megapixal camera my pictures will automatically be 300 dpi. I checked the resize dialog box and it says pixal size 3000 by 2400 but my file size is 55 by 25. So does this mean the image IS at least 300 dpi or ppi whatever the proper term is... Can I downsize that image and keep the same pixal range by unchecking the resample selection on photoshop. Help my deadline is the 21st. Thanks.
 You can easily change the DPI setting in the images using Photoshop without affecting the image. This is done in the Image Size dialog box with the Resample Image deselected. To "up-res" the image, you can change the DPI setting and have Resample Image selected.
 could someone please help,

i have a cannon ixus 850 is digital camera 7-1 megapixils, i have to send my photos in 300 dpi, should my photo be in a certain size before it is downloaded, i currently have my photos iin microsoft word awaiting pdft transfer thank you
 hi. i am an ameteaur photographer and lately i have been getting alot of people to want me to do pics for them and they want enlargements and all the websites are saying low resolution. but when i go to the picture and look at the pic info it says 350.000 dpi so i dont understand what the problem is. im afraid to pay for the pic and then it not come out and be stuck paying for a print that is all distorted. PLEASE hELP i am losing my mind over all this.
 The "DPI" value is meaningless... Instead, for a proper enlargement you will need to ensure that you have enough "pixel resolution". Look at the image dimensions -- if it is 3000 x 2000 (6 megapixels) or larger, one is usually capable of producing reasonable enlargements.
2010-08-02luke watts
 wow.....................wonderful explanation in post a well in Q&A part.I liked it..........Thanks for sharing.
In Photoshop, open your original photo, set the image>image size "resolution" to 300 and make sure you have "resample" deselected.Now when you save it and have a look at file>file info, it will show 300 DPI. Nothing is actually changing (unless you saved it as a JPEG which will compress the image each time you save it, losing quality), but it should keep the magazine company happy because they don't know what they're talking about. What they want is a high resolution (X by Y = pixel dimensions eg 2256*1496 px) image of high quality (point and shoot cameras like to have higher MP specs than DSLRs as a selling point but they produce lower quality images).
2010-07-09don drumm
 i just bought a panasonic lumix fz35 12.1 .i need to send pics for a magazine ad and they need 300 dpi. we sent pics and were told they only came through at 180 dpi. i only need a 2x2 pic. what is my problem. thanks, don..
 First let me say thanks for this super helpful discussion!! Like some of the other writers, I am being asked to send in 300 dpi photos for print. I have an 8mp camera but it only takes pics at a resolution of 180. I have the capability to upsample in photoshop from 180 to 300. But what effect will this have on my picture? What would be the final (good) print size that I can go to after upsampling an 8.0mp photo from 180 to 300 res?
 i'm using a canon ixus 75. i just realised its taking photos at 180dpi. i need 300dpi for print, and i'm worrying that by increasing the dpi in photoshop and keeping the image size the way it is (A3), my image will become pixilated. Can i change the settings on the camera so it takes photos at 300dpi?
 Augh! I've gotten so many different responses to the same question. Perhaps you can help! I have taken pix on my sony 7.2 megapixel camera that I want to enlarge to 20x30 poster size prints. What DPI setting should I use and how many pixels should I change the image to width x height? Also, I am using irfanview to change the image/resize; however when I change the pixels it automatically sets the other setting (be it height or weight) for me. Would this effect the print negatively (no pun intented) to have the DPI not perfectly relative to the pixels?? I was told to multiply the 20x30 by the number of DPI in order to get the right pixels, but when I do that, again, irfanview does not allow me to enter the exact number calculated. If you could help i'd reeally appreciate it. thanks!!!!
 Thank you, that's great. I have another question. Our Kodak DX7590 automatically downloads images in JPG format and print advertising usually requires TIF or EPS format. Sometimes I can get away with a PDF, but it's not always accepted. What's the best procedure for changing a JPG to a TIF or EPS file format without losing image attributes or clarity?

Thanks again.
 Hi- I do advertising design for my company. Most magazine print ads require images to be 300 dpi or greater. We have a Kodak EasyShare DX7590 which is 5.0 mega pixels. When I set the camera resolution to its optimal settings and download images taken at this setting, Photoshop tells me the dpi is only 230. Is there a way to up-res a digital image to 300 dpi in Photoshop for print publication? Please help.

Thank you!
 You can change the DPI to whatever you want in Photoshop without affecting the image. This is done in the Image Size dialog box with the Resample Image deselected. To "up-res" the image, you can change the DPI setting and have Resample Image selected.
 I have a Canon Rebel XTI the DPI on this camera is 72 that's the highest it will go. I can get up to a 12x18 canvas anything higher says low resolution. I've went to several sites and got the same thing. i was told to change the DPI in photoshop I did I uploaded the photo and tried to order a larger canvas same method. My question is who actually gets prints up to 20x30 with great quality, what camera are you using, and how much does it costs. It looks like I bought the wrong camera to do what I need to do. I might need another one. I've tried all the tricks and tips on the internet. i do understand my DPI at a 8x10 may be 300-400 but when it comes to large 20x30 prints it's just not enough :-(
I have a question about photoshop and cropping/printing. I am trying to fiqure out cropping and resoloution. I have a canon slr xti camera and fiqured out how to properly crop so that when I print, my photos come back the way I thought that they would. I am confused about resolution. In photoshop when I change my size to crop I was told to make sure that the resolution is no smaller than 300. Can I just leave the resolution blank?? If not, will a resolution of 300 be okay for all sizes of photos?? Do I just change the resolution on the display page in photoshop or do I have to go into image at the top and then go into the resize section?? I have alot of quesions...please help!!
 How many megapixels are needed for the best capture resolution for maximum print size of 20 x 30 inches?
 I have updated the chart to show what a 20x30 would theoretically require by the standard rule-of-thumb resolution guidelines. However, it is clear that such high resolutions are not very realistic. Instead, one tends to print images from source photos with far less resolution -- an expectation is that the viewer will tend to be further away from the image and hence will not be distracted by the lower resolution.
 I am giving a life like cutout of my husband made for a birthday party. I am told I need a picture of 300dpi of better, exactly how many megapixels is this?
 If you're told to provide a 300DPI image for a life-sized cutout, then it sounds like they don't really know what they're asking for! A 300 DPI image at that dimensions is virtually impossible to produce (nearly 100 megapixels). I think the best you can do is provide them with a file that is at least 8 megapixels, and they can try to enlarge (interpolate) this to fill the full size of your cutout. Most important is to take a picture that is sharply-focused and well-lit.
 Hi I am still a bit confused about the DPI thing. I would like to buy a small portable digital camera under $300. that i can print and occasional 8x10 maybe even a 16x20. Are the canon powershots good cameras for this?
 To keep it very simple, ignore the DPI calculations. Most digicams nowadays for $300 will be more than capable of 8x10 prints. 16x20 is still possible, but you'll probably want to start with a digicam in the 8-10 megapixel range. You can always get away with some limited up-sizing in Photoshop to make larger prints without it being noticeable.
 I currently have a Canon SLR EOS 20D camera with 8 Mp resolution. I would like to print pictures obtained from my camera on 11x14 paper or even bigger. The new Canon EOS 40d is a 10 Mp camera. If I desire to print on such paper sizes would it make much of a difference if i used the 10 vs. 8 Mp camera since to get 300Dpi i would need a camera with resolution of 13 Mp?
 In all honesty, I don't think one should get too hung up on the resolution guidelines. For starters, many people have had success printing 11x14 with 8 megapixels. Depending on the subject matter, the 300 DPI suggestion may more than you are able to discern at a reasonable viewing distance. The difference between 8 and 10 megapixels is quite small, and the lens choices plus manner in which you take the photograph can have a far greater impact. That said, you can generally up-res (enlarge) images in Photoshop quite effectively to output 11x14 @ 300 DPI, if that's your target. It is highly unlikely that casual observers will identify the uprezing in your final print.
 I have a canon ixus 75 and I'm not too concerned about the size of the image but I do want my images suitable for print at 300dpi. If I take my image on the largest, highest quality setting on the camera and then resize it smaller through increasing the pixels to 300 in photoshop, will I get the quality I want? thank you.
 At the highest quality and largest size, the Ixus 75 gives you 7 megapixel images (3072x2304). This is enough resolution to print very high quality (300 DPI) 8x10" photos (if you don't resize). However, I'm not sure I understand what exactly you may be doing when you say "resize by increasing pixels to 300" -- I believe you are simply changing the DPI setting from 180 DPI (the default) to 300 DPI in the Image->Image Size dialog. If the "Resample" checkbox is off, this won't affect the quality at all (in other words, you'll have more than enough quality) -- in fact, it doesn't serve much purposes at all (it depends on how you are printing). If you left the "Resample" checkbox on, then the image will be enlarged and quality will suffer somewhat. If I didn't answer your question, please let me know.
 I make 5-1/2" tall dolls and need to be able to email pictures to publications that are sharp and large enough for them to print. I know nothing about photography and have not been able to provide a picture that is large enough (when THEY open it... it's large for me) or sharp enough.

I have a SONY Mavica 3.5" 10X digital camera. Can you please tell me what my settings should be so the picture can be attached to an email and arrive the correct size and not be blurry? Thank you so much!! I'm desperate.
 i'm geting a nikon d50 and i just want to know will i be geting 300dpi pictures from this camera?
 Absolutely -- the D50 gives you 6 megapixels to work with, so that's enough resolution (3008x2000 pixels) to print a 10" x 6.7" photo at 300 DPI or a 15" x 10" photo at 200 DPI. Most people will be happy with photos printed at anything over about 240 DPI.
 Hello there.
I read your article and it is very informative. However, I have a question to ask regarding the dpi. I brought Panasonic Lumix FX50 and the maximun dpi is 72 dpi. Compare with another camera like the canon ixus series, the maximun dpi is 180 dpi. when i use my personal computer to compare both photos taken with the same resolution from pansonic and canon, I find that the photo taken from the canon is much more sharper. And when I zoom in the photos, canon still produce sharper image than panasonic. Does that mean higher dpi is better ? If yes, then I guess camera that offer superfine image quality is better than camera that offer only fine image quality. Thank you for reply
 There are three issues that you have brought up... it turns out that none of them are actually related! I'll try to give you an idea of each:
  • DPI - The DPI setting that each camera sets for an image is essentially meaningless. They could have set it to 1000 DPI and it would not have changed the image. The DPI setting is basically a way of telling your photo software / printer what the default image size should be, but you can set it later to whatever dimensions you like (at the expense of resolution). This DPI value has confused a lot of people!
  • Image Sharpness - Most digital cameras require some degree of sharpening (due to the way that the sensor is arranged/used). Point and shoot cameras tend to do this in-camera, while digital SLRs leave it up to you. If you are seeing differences in image sharpness for the same composition, etc., then it may be due to differences in quality of the lens, the use of digital zoom, and image processing in the camera itself. Canon is fairly well regarded for image quality, so it wouldn't be too surprising to see a difference.
  • Image Quality setting - Unfortunately, the names and meanings of the quality setting is completely vendor-dependent. In other words, each manufacturer chooses its own names for their highest image quality setting. Some use fine while others use super fine or maximum. You cannot compare quality settings between different manufacturers for many reasons (if you are interested in the details, read about quantization tables). But, in general, one should always use the highest quality setting, and simply reduce the image size if you are tight on space. Lower image quality settings (while they reduce file size) introduce some pretty unpleasant compression artifacts that may be much more frustrating than a smaller image!
 my questinon is I have an Canon 8mp, DSLR and i was wondering, does photoshop do a pretty good job of enlarging photos for print?, and is it necessary to increase the dpi above 300 in any case?
 Yes -- Photoshop does quite a decent job at upsizing images. Although if you are intending to upsize significantly, then you may want to check out other tools such as Genuine Fractals. Starting with 8 megapixels gives you quite a good starting point. Most people will never be able to output to a device capable of reproducing their images in a resolution above 300 dpi, so there is little need.
 Hey, you must be a nighthawk like me! Thank you very much for your prompt reply and explanation. Just one last question. When you suggest superfine refers to the level of compression and contributes to overall image quality, does that mean negatively? Should I have it set for a lower compression then? Or leave it on superfine?
Thanks again!
  Superfine mode uses the least amount of compression, which translates into the highest image quality. In general, I don't think that one should ever set the image quality mode to anything other than superfine -- if file size (or number of photos per memory card) is an issue, then use a lower resolution mode, not lower image quality (higher compression). I would rather have a smaller image (in terms of resolution) than to deal with more compression artefacts (which are not particularly nice).

This is one of the ways in which the digital format differs from film -- in film, people have grown accustomed to some degree of film grain. Digital noise and JPEG artefacts are not nearly as accetpable. Low compression artefacts are disturbing because they are easily identified by their repetitive patterns and hard-edged nature (not organic).
 Hi, I've got a serious question and sure need some help. I have a Canon PowerShot A510 3.2 Mp and this relates to your note about why the camera is set at 180 res. I've got mine set on superfine large and can't get any more than 180 res. even if I go to superfine small. I don't mind only being able to print at 4x6 or 5x7 as long as I can do so at 300 dpi. I am trying to produce commercial postcards and have the printer that's capable, but on downloading my photos,whether in Photoshop or Canon's software, I can't get the res any higher than 180. I've tried changing the image to a smaller size but higher res in Photoshop but that isn't improving the pics any. Can you help? How do I change it? Or can I?
Thanks for your answer ahead of time! I need all the help I can get. I've left my personal email with you.
 Hi JB --

You don't need to, and in fact cannot, change the DPI resolution as recorded by your camera. To be completely honest, it's a meaningless number. Your camera records a fixed number of pixels (3.2 million) in large mode. It is your choice (in the photo editing software) what physical dimensions you want for the final print. Obviously, the larger the print, the lower the DPI that you are effectively using.

When enlarging, it is best to choose a minimum DPI that is acceptable for your final output (most people aim for 300 DPI, but 240 or even 200 may be acceptable). Since your camera records 2048 x 1536 pixels, this means ~ 5" x 7" @ 300DPI, 6.5" x 8.5" @ 240DPI or 8" x 10" @ 200DPI. You can define this resolution (or conversely, output dimensions) in Photoshop (via the Image Size dialog using the Resample option). This will override any DPI setting that your camera may have written into the original file. The whole concept of DPI settings from the camera has certainly confused a lot of people!

Just as an aside, the superfine mode simply describes the level of compression that you are using (not resolution), which is another contributor to overall image quality.
 What is the best dpi size to set up some 4x6 photo to get printed.
i wont to supply a client a CD of imager that they can print out ONLY them self’s at 4x6. so they can not enlarge them and have to come back to me for the enlarges

 i am very new at digital cameras i am getting my first one in a couple of days it is a kodak c350 i just dont know what batterie i shouild have it takes double aa but i wouild like to use a litronum batterie do thay last longer then the reculer batteries i also wouild like to use my moms computer she has a nikon color pix
 Edie -- You're going to have a lot of fun! If it takes AA batteries, then you'll probably be better off in the long run buying rechargeable Lithium Ion (LiOn) batteries instead of the regular alkaline batteries, as it will be cheaper. However, Lithium Ion batteries do not have the same starting voltage as the regular batteries, so they will likely not last as long. Most people use the shorter-lasting rechargeables as it can be much cheaper in the end, especially if the camera is power-hungry! If you're worried about battery life, you can get used to taking photos with the display turned off.
 Refering to the format of 300dpi, I have a (4.4mp) (2576 × 1716) camera and I am about to send pictures for a mag publication that require a digital photo shot at 300dpi 11x17 in.and no resizing. Is my camera up to the required resolution? Or how many megapixel do you need in order to comply for this format?- Thank you-
 Cecile -- If the magazine is asking for 11x17" at 300dpi (without resizing), then you're not really going to meet what they've asked for. 11x17 is 187 sq in, which is just over 16 megapixels at 300 dpi. Most often, people can get by with printing at a lower DPI (eg. 240 dpi) and can tolerate some degree of resizing, but it really depends on the image content. That requirement might even be asking a bit much from most 35mm film shots. You might want to confirm that these are strict requirements.
 I have a Canon Ixus 55 (5.0MP) and I want to enter a competition. The rules say that the photos should be of resolution 300DPI? what does this mean?is my camera up to the task?
Thank you!
 Realistically, the rule makes very little sense. It sounds to me like their photo competition is geared more towards film entries than digital entries. If they accept digital photos as entries, then all that they should be concerned about is the pixel resolution; 5 megapixels in your case is generally more than enough. In the digital photo world, DPI is almost totally irrelevant. (In fact, you can set it to whatever value you like!)

What I believe they may be refering to is the resolution selected when scanning photos that were taken with film. Scanning a typical 4x6" print (processed from film) at 300dpi will deliver a pixel resolution of about 1800 x 1200 pixels, or just under 2.2 megapixels.

For most judging purposes, 2 megapixels should be reasonable enough to make an assessment of the merit and quality of a photo. Therefore, I feel that submissions direct from your Canon Ixus 55 should be more than fine for their competition rules. Good luck!

I've been trying to get people to think in terms of the number of *independent* pixels in the image. More pixels doesn't necessarily mean "better picture" if, for example, the lens resolution isn't up to the task.

This is especially true with point-and-shoot cameras, which have gone from 2 Mp (or less) up to 5-6 Mp in recent years without any increase in sensor size -- which they have to keep small to keep the lens and the rest of the camera relatively small, the battery life up, etc.

At about 5 Mp the individual pixels are about 2.4 microns in each dimension, which requires a lens to be able to resolve over 400 lines (or 200 line pairs) per millimeter for each pixel to be seeing something different in the original scene being shot. Manufacturers generally don't quote the figures for what their lenses can do, but I doubt anyone could afford a 400 lines/mm lens.

The moral is that you're not getting the number of pixels you think you are unless the designers have made a very good match between the optics and the sensor. It's always less, when looked at from an information flow perspective through the entire system. So generally the only way to get more real Mp's is to get a bigger sensor.

* MB

P.S. - "Why do some Canon camears set the resolution to 180 DPI?" I think you're basically right. In practice, even 125 DPI can be OK for casual use. People have become so accustomed to the low-res nature of TV that just about anything goes as far as the non-photographer is concerned so long as the individual pixels don't leap out at you.


Great comment! Yes, absolutely. No discussion of megapixels should be without mention of its relationship with the sensor size and the lens. Many of us were shocked when the first 8 megapixel digital Point & Shoot camera came out, the Sony F828. It didn't take long before it's terrible noise characteristics became news -- a function of the pixel element size (and poor signal-to-noise). You mention the other side to this, the lens' resolving power -- this is almost never mentioned because there is no obvious metric that can be used as a selling point for the average consumer. Most people will assume that the lens doesn't have any important characteristics other than its zoom range. Very few will ever go and look at the MTF charts on Photodo, but this is the missing element. Thanks for your insight.


do you know about a similar web site in french?

thank you.


Hi -- In all honesty I am not sure, but if you like, you can get Google to translate any parts of this website (or any others) if you like. Simply go to:

Google Translate

Then enter my web page address into the box titled: Translate a web page, select English to French and press Translate.


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