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Monday, March 06, 2006

How Many Pixels Do You Need?

Three mp makes a perfectly nice 5x7 print.

Start by taking a good file and making test prints at 360, 300, 240, and 200 ppi.

Choose which resolution looks best on your paper and printer.

Now decide how large you want to print as your standard size. (Hint: For occasional large prints, either send it out to a professional lab, or use an "uprezzing" application such as FixerLab's SizeFixer. Remember that larger prints will be looked at from farther away.)

Multiply each dimension by your chosen resolution, then multiply the two. Voilá. That's how many megapixels you need.

For example: My standard print size is 7 x 10.5 inches. If I want to print at 300 ppi, that's (7 x 300) x (10.5 x 300) = 6,615,000 pixels = 6.615 effective mp.

To find out how big your existing camera can print (optimally), just go the other way.

And here's what a lot of people don't get. If you regularly print smaller than the optimum size for your files, you're just throwing the extra information away. An 8x10 print at 300 ppi needs (8 x 300) x (10 x 300) = 7.2 mp. Call it 8 mp and give yourself a little leeway for cropping. (And remember that that's without NR or uprezzing, and 300 ppi is overkill for many printers.) Once you've got that covered, having a 12 mp, or 16 mp, or 22 mp camera is not going to make that 8x10 look any better. Your printer can't print better than the best it can print; if you're already giving it all the information it can get onto the paper, giving it more won't help.



Anonymous Josiah Davidson said...

Thanks Mike. Good rule of thumb and generally good advice. But not completely accurate. I'm an old large format guy (8x10) and medium format (4x5). My 17MP 1DsMkII does "ok" at 11x17 (double page spread). The problem is how the Bayer matrix handles (or doesn't) the fine detail in landscape photos. The Bayer's luminosity resolution is sort-of as stated (not counting the loss of the low-pass filter – maybe we need a stochastic sensor?!), but its color resolution is only a fraction of that. It roughly takes the reading from 9 pixels to determine the color of the pixel in the middle of that nine pixel grid. I suppose that is partly why fine foliage detail in landscape photos looks sort of smeared compared to what you get with film or a scanning back or Foveon X3.

Anyway, my main point is that I don't want you to discourage Canon from coming out with their $3,000 75MP 1DsMkIV. THAT is THE camera that tens-of-thousands of us large-format landscape photogs NEED to satisfy our hunger for clean, fine detail on reasonably sized prints (up to 20x30).

By the way, thanks for doing this great website. Your columns were too few and far between.

1:50 AM  
Anonymous Anonymous said...

I can't be alone in the situation that printing, by and large, no longer matters to me, simply because I never print.

I have photography as a hobby. For that purpose, I display images exclusively online; sometimes in my Flickr album, and sometimes for use as illustrations on my (likewise utterly amateur) blog. I also use photography as a tool for my work as a researcher; but there again, I view images on a screen, transfer with email and so on.

I'm not at all against printing. I have a long-standing idea that whenever I want to have a good print of any of my images, I'll not skimp on price, but go to a good printshop and have it done for real - it's worth it. Of course, for the past three years it hasn't happened yet. I mean, what would I do with it? More likely than not, it'd end up unviewed in some file folder and get lost when I next move house.

So for me the question of resolution becomes one of pixels - what pixel size should you be able to display the image at for your viewers to see it at a reasonable angular size without having to scale it up. 1600x1200 will cover all but the most extreme monitors (and they will tend to be large, so covering all of it isn't too important). If people want to see it on "HDTV", or on a normal monitor (considering the controls and other paraphrenalia of a browser) it's enough to aim for the 1024x768 territory. To put it into perspective, a Hollywood blockbuster has its computer-generated scenes rendered at about 4000x3000 pixels (or 12Mp) and is shown on pretty humongous screens with little or no visible artefacts.

Let's be wasteful and say you need 5mp. Anything over that is just margin for cropping, or spatial latitude for editing before you downscale it.

5:44 AM  
Anonymous Anonymous said...

I think a lot of people don't understand the change in photography that is coming. A few years from now, picture printing will be close to obsolete. Printing will become like film is today, on its way out except for a very small minority. Like everything in this world, it keeps getting more expensive. Printed magazines will eventually go the route of online only or go out of business.

Individuals are getting tired of paying for paper and ink. Its too expensive and more work to print than its worth. Looking at pics on their computers is easier and much cheaper.

The only printing that's guaranteed to stay is business laser text printing. They will never stop printing bills, collection notices and some advertising.

8:10 AM  
Blogger Mike Johnston said...

Josiah, loved that comment (medium format!), thanks.

Anonymous, your comment is interesting to me too--having long been a connoisseur of prints (I did it for a living for a while, and have inspected LOTS of historical originals in my day) I have to say that generally I really like viewing pictures on a monitor. It's akin to a virtual slideshow without the hassle and the darkness and the noise of the fan. The colors are clean, shadows open, and resolution is almost removed as an issue because everything is reduced to 72dpi, which just sort of forces you to look at the image and not get distracted by technique. (Of course, "get distracted by technique" pretty much defines what photographers do online....)

I still like prints. But the monitor is a very democratic viewing medium and quite pleasing in its own right.


P.S. I almost hate to admit this (I sense it will come back to haunt me (g)), but sometimes--very occasionally--when I find somebody's picture that I really like and want to look at properly, I'll download it and correct it in Photoshop like they should have done if only they'd known how...of course I don't KEEP it, I just want to see it "done right"....

8:12 AM  
Anonymous Anonymous said...

I do print, but those boxes of loose prints are starting to annoy me. How do I frame them for less than a King's ransom? I know, there are chrome, black and other colored metal frames, but they often look pretty underwhelming. When will someone actually define a 13x19 framing approach that makes sense and is additive to the presentation. While the photo acquisition arena has certainly seen some gains lately, our framing options are stuck in the 60's. DVD's with high quality images can certainly be enjoyable to watch, but this should be an alternative as opposed to the "only good way" to really enjoy your photographs.

Does anyone know of some good display solutions using prints?

9:59 AM  
Anonymous george said...

Generally speaking large prints will be viewed from a distance but I also like to go close in and look at details. The big downside with digital prints is that you just confront smeared detail and pixels if viewed closely. Yuck !

11:42 AM  
Anonymous Christopher J. May said...


Liked this article. I think a lot of people get caught up in the Megapixel race and forget about the rest of what counts in photography (e.g. good glass, proper techniques, etc.).

I would kind of liken it to the horsepower race in the automotive realm.. Horsepower is nice, but it doesn't mean a lot if the transmission, rear end, suspension, brakes, etc. aren't up to par as well.

As an example, I have this:

printed at 20"x20" on my wall at work. If I had printed full frame, it would've been 20"x30" The crazy thing is that it's an upressed 10D file. But, it was taken with a 300mm f2.8L IS (a lens I have a personal affection for), on a monopod, at ISO 200 to give myself one extra stop. Since the original file was pretty much flawless, upressing was pretty easy, and the print is stunning.

I doubt most amateur photographers ever print anything past 20"x30" so I'd personally make a case for 6 MP with good picture-taking practices.

Just my 1/50th of a dollar of course.

12:53 PM  
Anonymous graham said...

Boxes of loose prints? Or worse still, only looking at images on-screen? I've got several large boxes of exhibition sized prints that don't get viewed very often and take up loads of space.

One great upside of this digital age is that we can print small, and print consistently. So I've started making books of my prints. It doesn't have to be anything too elaborate. I use an office comb binding machine and use heavy card or plastic for the covers, and standard photo quality paper for the images. I usually make these books A5 size, so they are quick
and economical to print. When completed, you have something that looks neat, is easily passed around and viewed and is a permanent collection of your work. Furthermore, they fit neatly on a shelf and with modern pigment inks are going to last a lot longer thaan me or my volatile digital data. I can't see the point of making pictures if nobody is going to see them.

1:06 PM  
Blogger eolake said...

Mike said: "I have to say that generally I really like viewing pictures on a monitor."

I hear you. I really found out about this when I got an Apple 30 inch monitor. (I realize this is still out of many people's reach.)
When I bought it, I thought I was really endulging myself. But apart from the wonders it has done for my workflow, what really bowled me over was simply looking at photos on that thing. It was a whole new experience of photography.
In a few years when they become really cheap, you can have them around your home with changing pictures on them.

2:21 PM  
Blogger Dave New said...


eolake hit the nail on the head. Especially for folks that don't have a ton of wall space for hanging prints, the next best things (and probably soon to be considered even better than prints) will be one or more 'digital frames', both wall-hanging types and desktop frames.

We've already seen the desktop frames, in various forms, but most of them have some strings attached, in the form of a required subscription to an online picture service, to keep the frame fed. This subsidizes the price of the frame.

At some point, though, the price will get cheap enough on its own that folks will be able to buy a small one for about the same price as an empty print frame from K Mart (you know, the kind with some dumb poster in it, you throw away, just to get the cheap frame).

The challenge, then, for folks that make their living off of selling fine are prints, will be to find a way to market their stuff to folks that only need to stuff a compact flash into a slot on their wall frame, and get a series of changing pictures.

I can't predict what kind of pricing model will evolve, but it will change the entire fine art print business. The key will be to be on the vanguard, rather than hanging on for dear life in the rear ranks.

2:37 PM  
Anonymous Gustaf said...

Just a quick comment. A 6 mp image from a digicam won't have as good "pixel quality" as a 16 mp image downsampled in some clever way to a 6 mp image. If you look at a 200k web jpg up close, you can usually still see clear, crisp detail at the pixel level. Not so for the original file.
That's not to say that 6 mp isn't good enough, but rather that if you're nitpicky, there is a difference between two images printed at the same resolution if one started as a 16 mp and the other as a 6 mp file.

12:20 PM  
Blogger bokeh said...

My reading of the "Nyquist Theorem" is that you need twice the bandwidth of the final image to produce a high quality result. A 6MP camera like the Maxxum 7D produces a raw image of 3008x2000 pixels. Divide the vertical and horizontal bandwidth by 2 and you get a 1504x1000 pixel image which corresponds to the small image setting in the camera. Thus the Maxxum 7D is really a very good 1.5MP camera. A 24MP sensor would make very nice 6MP images. Maybe we do need those big sensors after all.

2:47 PM  
Anonymous Anonymous said...

The digital age, not just photography, is all about a trade of permanence (and for some, quality) for the ability to distribute quickly, infinitely and freely. Physical objects like prints, CDs/DVDs or any physical media become insignificant.

This newly found freedom means that your grandchildren may never find that shoebox of prints in your basement after you're long gone. Whether that's a bad thing is a matter of opinion. Nothing in the universe is permanent, but somehow we would like to think so (in the west anyway).

Someone said to me the other day, that in Japan people are used to bad prints. I am not sure if that's true, although I see a lot of digi prints like from 1.3MP camera phones which seem acceptable to people. What may happen is that we are getting used to "lower" quality and loss of permanence, in return for better distribution, which is what we want, and in the end nobody will miss anything.

I keep noticing that it is always people who have been around in the medium for a while come up with those "complaints". The kids of today will not even now and nobody will miss film or the fine print, just like I don't miss the daguerrotype. I would hate the photographic community to become a "they don't build them as they used to" circle.

It hasn't been this exciting for a long time.


10:21 PM  
Anonymous Karaya said...

Interesting Discussion here.Photography, and what it means to people, really is evolving rapidly. Personaly, I just got serious, or 'into' photography 2 years ago when I got my Olympus E-1.I never really did anything with film. I guess I would catagorize myself as an enthusiastic amateur. I like looking at digital slideshows (at 1600x1200) on my 20" monitor. I also have printed ~200 photos as 8x10s (~240ppi) on my own printers, as well as a dozen, or so, of my very best shots that are framed 12x16 and 16x20 prints hanging on my walls. These were expensive, but I love looking at them everyday as I move about the house. They are like old friends at this point.

I also just got done shooting a sci-fi convention. ~800 geeks of all ages. Their attitudes about digital photography are interesting. I provided the con webmaster with 90 down rezzed jpegs for the con's website. I also offered to sell prints to anyone who had a favorite pic. Well, so far one sale. I hope I get more sales, but I would not be surprised if I do not. I saw maybe 2 or 3 other DSLRs at the con, and hundreds of little silver digicams, held out at arms length, flashes poping away...Well, what am I trying to say here, it seems to me that what most people like the most about digital photography is the conveniance, freedom and inexpensiveness compared to film photography. They want their pics now, and at little or no cost. Most know nothing, and care nothing about quality, except for a vague faith that more megapixels is better! I am a little worried about the future. Look what has happened to hi-fidelity music. People consider big speakers and amps passe as they amble along listening to their i-pods! Are camera phones the future?!

3:48 PM  
Anonymous Anonymous said...

One thing that needs to be considered in the "more megapixels" race is that if the camera makers really _do_ bring out anything like the 75 Mp 1DSMKIV that an earlier poster mentioned, they will also have to bring out a whole new set of extremely expensive lenses so you can actually make use of all those pixels. For example, read the dpreview comparison of the 1DSMKII with the Nikon D2x--the D2x did better in some comparisons, despite having 25% less pixels, because the lenses on the Canon couldn't out-resolve the sensor at the edges of the image. I found similar effects when I bought a D2x; had to replace some lenses because quality that looked fine on film, and on an older 6Mp DSLR, obviously limited the performance of the APS-C 12 Mp sensor on the D2x. If you do the calculations, the D2x requires somewhat more than 50 lp/mm across the field to get the best out of its sensor. A 75 or so Mp Canon, with a full-frame 24 X 36 sensor, would produce an image of about 7000 X 10,500 pixels, and would need a lens that resolves 145 line pairs/mm across the field to take full advantage of its potential. Without some major advances in lenses or image processing, this is not going to happen.

5:41 PM  
Anonymous Josiah Davidson said...

But such lenses already DO exist (see on this website).

Alternatively, that is the reason for larger format. If we can only make lenses that resolve 50 lpm, then simply make a sensor that is physically big enough to hold enough lines to get the desired resolution.

But if Canon, Nikon, etc. would get on the ball and start making REALLY good lenses with existing technology, we'd all be ok with a 24x36mm sensor size (once they improve the s/n ratio at that pixel pitch).

My point is that MANY of us truly want and need that kind of resolution for the work we do.

If you are doing close-ups or portraits of people or animals, you don't need it (medium and close-distance shots give the illusion of greater resolution). If you are doing shots of kids jumping in the pool, you don't need it. If you are satisfied with fuzzy 35mm film equivalent quality, you don't need it.

But if you are doing high-qulaity detailed landscape or architectural/interior work (as seen in a few high quality magazines), you need more resolution and image quality than the 17MP 1Ds2 can give you.

10:55 AM  

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