# What's the dots per inch equivalent for photographs? **URL:** \ **Category:** Factual Questions\ **Created:** [May 5, 2003, 7:54pm UTC](https://boards.straightdope.com/t/whats-the-dots-per-inch-equivalent-for-photographs/173258 "2003-05-05T19:54:53Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![El\_Smasho](https://avatars.discourse-cdn.com/v4/letter/e/f9ae1b/32.png) [@El\_Smasho](https://boards.straightdope.com/u/El_Smasho)\ **Post date:** [May 5, 2003, 7:54pm UTC](https://boards.straightdope.com/t/whats-the-dots-per-inch-equivalent-for-photographs/173258/1 "2003-05-05T19:54:53Z")
How much resolution would a digital camera need to actually beat out a film camera? ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [May 5, 2003, 8:04pm UTC](https://boards.straightdope.com/t/whats-the-dots-per-inch-equivalent-for-photographs/173258/2 "2003-05-05T20:04:23Z")
That’s not something that’s easily quantifiable, since film is not made up of dots and the quality varies greatly depending on emulsion speed, exposure time, aperture and type of lens. ---
**Author:** ![Patty\_O\_Furniture](https://avatars.discourse-cdn.com/v4/letter/p/96bed5/32.png) [@Patty\_O\_Furniture](https://boards.straightdope.com/u/Patty_O_Furniture)\ **Post date:** [May 5, 2003, 8:09pm UTC](https://boards.straightdope.com/t/whats-the-dots-per-inch-equivalent-for-photographs/173258/3 "2003-05-05T20:09:20Z")
That’s like asking how many times oversampling would you need before you had a true analog signal coming out of a DAC. Since there will always be some quantization error, the digital approach to a true analog format will be asymptotic. Approaching it, but never reaching it. We will probably at some point get the error low enough that it just doesn’t matter any more, but for those who want to split hairs we will never beat it. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [May 5, 2003, 8:17pm UTC](https://boards.straightdope.com/t/whats-the-dots-per-inch-equivalent-for-photographs/173258/4 "2003-05-05T20:17:37Z")
I once heard around 12 million dpi but it is a vague memory. Of course, film itself varies in its resolution capacity so this would be a pretty loose rule. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 5, 2003, 8:22pm UTC](https://boards.straightdope.com/t/whats-the-dots-per-inch-equivalent-for-photographs/173258/5 "2003-05-05T20:22:11Z")
It depends on the film speed. Really slow, fine-grained films will never be beaten digitally, I think. On the other hand, really fast coarse-grained films can be beaten now. I once saw a tiny bit of a 35 mm ISO 25 negative blown up over 2000 X with little loss of definition. Come see me when your digicam can do that. ---
**Author:** ![viking](https://avatars.discourse-cdn.com/v4/letter/v/bc79bd/32.png) [@viking](https://boards.straightdope.com/u/viking)\ **Post date:** [May 5, 2003, 9:42pm UTC](https://boards.straightdope.com/t/whats-the-dots-per-inch-equivalent-for-photographs/173258/6 "2003-05-05T21:42:47Z")
> [@](#): > > \*Originally posted by Attrayant \* > \*\*That’s like asking how many times oversampling would you need before you had a true analog signal coming out of a DAC. Since there will always be some quantization error, the digital approach to a true analog format will be asymptotic. \*\* Almost, but not quite. Film is made up of really small particles, each of which has a given darkness. They are just more randomly shaped, sized, and distributed that say pixels on a screen. But if you sample to the point that you’re getting many pixels per particle of film emulsion, then you would exceed the resolution of film. I had a bunch of slides taken with Fuji Sensia 200 (iirc, which I might not) through not quite long enough a lens, so I tried popping them under a dissection scope (~15-20x, again iirc) and hit the limits of the film, in that I started seeing graininess. Slower films tend to have smaller particles (the increased surface area to volume ratio is what makes the film faster), so the effective resolution is better. ---
**Author:** ![Omphaloskeptic](https://avatars.discourse-cdn.com/v4/letter/o/bcef8e/32.png) [@Omphaloskeptic](https://boards.straightdope.com/u/Omphaloskeptic)\ **Post date:** [May 5, 2003, 9:50pm UTC](https://boards.straightdope.com/t/whats-the-dots-per-inch-equivalent-for-photographs/173258/7 "2003-05-05T21:50:13Z")
I’m not an expert on this, and it’s a complicated subject because in going from film to digital there are a lot more changes than just the recording medium. For example: CCDs are “faster”, requiring less light than most film. The CCD area is also a lot smaller, meaning that the lens can also be smaller. This probably makes it easier to make high-quality lenses if the other design constraints remain constant, but of course a lot of digital cameras have much smaller space allotted to the lens than 35mm SLRs, for example. But anyway, a common measure of film performance is the resolution measured in “line pairs per millimeter” (lp/mm), which is the number of black-and-white lines, per millimeter on the negative, which can be resolved as lines rather than a uniform grey. (You can also try to resolve line pairs with lower contrasts between the lines, a harder test to pass.) Even though film is an “analog” medium, the grain of the developed negative gives an effective limiting pixel size, at least approximately. Really good films tend to have values of about 150 lp/mm for color, and 300 lp/mm for black-and-white. (Here’s a [table](http://medfmt.8k.com/mf/lenslpm.html). There’s a lot of good information in this link besides the table, too.) For a 3 or 4 megapixel digital camera, with about 2000 pixels across the image, this is about 60 pixels/mm when enlarged to the size of a 35mm negative. This implies that a reasonably good 35mm film is the equivalent of about a 15-20 megapixel digital camera. I’m sure someone who actually knows about the subject will be along shortly to explain how this is an utterly simplistic view, but that’s my understanding of it. ---
**Author:** ![lissener](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lissener/32/6139_2.png) [@lissener](https://boards.straightdope.com/u/lissener)\ **Post date:** [May 5, 2003, 9:52pm UTC](https://boards.straightdope.com/t/whats-the-dots-per-inch-equivalent-for-photographs/173258/8 "2003-05-05T21:52:08Z")
And now for the practical answer: Decent print resolution is 300 dpi; “fine art” print resolution is 600 dpi. Anything more is overkill. ---
**Author:** ![x-ray\_vision](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/x-ray_vision/32/351_2.png) [@x-ray\_vision](https://boards.straightdope.com/u/x-ray_vision)\ **Post date:** [May 5, 2003, 9:56pm UTC](https://boards.straightdope.com/t/whats-the-dots-per-inch-equivalent-for-photographs/173258/9 "2003-05-05T21:56:55Z")
Doesn’t that depend on the size of the picture **lissener**? ---
**Author:** ![Padeye](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@Padeye](https://boards.straightdope.com/u/Padeye)\ **Post date:** [May 5, 2003, 10:01pm UTC](https://boards.straightdope.com/t/whats-the-dots-per-inch-equivalent-for-photographs/173258/10 "2003-05-05T22:01:32Z")
I think you’re vastly overestimating the ability of film Q.E.D. The only ISO 25 film I’m aware of is Kodachrome wich is astonishingly fine grained (and not available anymore AFAIK :() but a 2000x magnification, let alone one that doesn’t show grain is out of the question. If you don’t crop that’s a 35mm negative blown to cover most of a football field. That’s a print 157ft x 236 ft. I think you have a couple of extra zeros there. A 16x20 **inch** print from Kodachrome 25 is possible but will still be grainy compared to medium or large format film. As for comparing digital resolution to film there’s an old saying. Figures do not lie, but liars sure can figure. I don’t think it’s possible to make a conversion factor that is satisfactory in all cases. A lot of photographers consider 5-6 million pixels adeqate for what would normally be shot with 35mm film but that isn’t to say that it’s the **same** as 35mm film. Not all pixels are created the same. I have a 5mp digital camera wich has a relatively small size 2/3 CCD. It’s very good but is still a prosumer camera, not true high end. The same number of pixels from a physically larger CCD as in a DSLR which is about the same size as a APS film frame will have significantly better dynamic range and a better signal to noise ratio. The images from the bigger CCD will look better, and more like film, than those from my camera particularly when light is poor. ---
**Author:** ![FranticMad](https://avatars.discourse-cdn.com/v4/letter/f/c68b51/32.png) [@FranticMad](https://boards.straightdope.com/u/FranticMad)\ **Post date:** [May 5, 2003, 10:07pm UTC](https://boards.straightdope.com/t/whats-the-dots-per-inch-equivalent-for-photographs/173258/11 "2003-05-05T22:07:23Z")
Here’s a link to a review of the [Canon EOS 1Ds](http://luminous-landscape.com/reviews/cameras/1ds/1ds-field.shtml) 11 megapixel camera. The quality of the results is astounding and far better than your video monitor. There are a number of technical issues in making a fair comparison, but the author concludes that this Canon is as good as, or even better than, film. If you only need prints up to 11"x17" and have lots of money, then you can get a Canon 1Ds and say goodbye to 35mm and medium-format. ---
**Author:** ![absimia](https://avatars.discourse-cdn.com/v4/letter/a/bbe5ce/32.png) [@absimia](https://boards.straightdope.com/u/absimia)\ **Post date:** [May 5, 2003, 10:07pm UTC](https://boards.straightdope.com/t/whats-the-dots-per-inch-equivalent-for-photographs/173258/12 "2003-05-05T22:07:44Z")
Much of what was said regarding the speed of the film, size of the negative, and whatnot is entirely true and important. Generally speaking, the slower the speed of the film, the more generous it will be when you blow it up. Very high speed films look grainy pretty much all the time. It isn’t a perfectly 1 to 1 comparison. However, along the same line of reasoning as **lissener** , it has been my experience as a graphic designer that you can blow up a 35mm slide to about 8" by 10" and have it look perfectly swell printed (we print at 350dpi). We have blown up 35mm slides to 17 by 23 or so and they look pretty good, but they do look kind of soft. ---
**Author:** ![norinew](https://avatars.discourse-cdn.com/v4/letter/n/eb9ed0/32.png) [@norinew](https://boards.straightdope.com/u/norinew)\ **Post date:** [May 5, 2003, 10:28pm UTC](https://boards.straightdope.com/t/whats-the-dots-per-inch-equivalent-for-photographs/173258/13 "2003-05-05T22:28:44Z")
Because they use different technologies to capture images, I do not think it is possible to make a direct comparison. Film is measured in ISO (international standards organization) speed, with the film having less sensitivity but better resolution as the speed goes down. So 100 iso film is twice as sensitive as 50 iso, but has only half the resolution. Why this is true is that at the molecular level, speed (or sensitivity) is determined by the physical size of the silver nitride crystals that are used to react to the light. Bigger crystals are more sensitive (more chance of being hit by a photon), but you get less of them for a given area of film. Smaller crystals need more light (more photons) to react, but due to the increased number of crystals the resolution is better. As if this were not confusing enough, you can vary the iso when you take the picture and then alter the developing process to account for it. I have taken pictures using 400 iso film set to 1600 and got usable (but not great) pictures. Going the other way works just as well. This kind of variance just does not exist in the digital world. Digital is fixed, with a set number of pixels, and as a result you generally have less quality under the same conditions as film because you cannot vary the sensitivity of the pickup device the same way you can with film. If you try to take a picture that is outside the capability of the pickup device you will not get as good a picture, as a digital pickup device is set in its sensitivity to light. That is not to put digital down, I love the convenience of not having to develop my pictures and it makes me a much better photographer because I can see my pictures while I am still able to take more if the ones I have are not good enough for me. This is assuming that conditions are right for my digital camera. If there are any special conditions, such as low light or long focal length, I will still use film. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 5, 2003, 11:06pm UTC](https://boards.straightdope.com/t/whats-the-dots-per-inch-equivalent-for-photographs/173258/14 "2003-05-05T23:06:22Z")
> [@](#): > > \*Originally posted by norinew \* > **Why this is true is that at the molecular level, speed (or sensitivity) is determined by the physical size of the silver nitride crystals that are used to react to the light.** that would be a silver halide, usually silver iodide or occassionally silver bromide. ---
**Author:** ![Padeye](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@Padeye](https://boards.straightdope.com/u/Padeye)\ **Post date:** [May 6, 2003, 2:44am UTC](https://boards.straightdope.com/t/whats-the-dots-per-inch-equivalent-for-photographs/173258/15 "2003-05-06T02:44:26Z")
**norinew** , I beg to differ that the quality of a digital camera’s image can’t be altered. True the photosite size is fixed but there is a correlation between ISO sensitivity and quality as with film but it’s for different reasons. Setting a higher ISO sensitivity electronically forces the camera to make an image with fewer photos for a given exposure than at a low ISO. This means more random noise from pixel to pixel. It isn’t the same as larger grain in a fast chemical film but the end result is remarkably close. Decreasing the sensitivity has the opposite effect, increasing color saturation and reducing noise. You have an enlightened view toward digital. It certainly isn’t ready to replace film and it’s debatable that it ever will be but there will be a place for both in the next few years. Lately I find myself using 35mm film less, digital more and and moving into medium and large format film for some paying work like portraiture. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [May 6, 2003, 3:40am UTC](https://boards.straightdope.com/t/whats-the-dots-per-inch-equivalent-for-photographs/173258/16 "2003-05-06T03:40:04Z")
[Film vs. Digital - Are 6 Megapixels enough? August 2002](http://www.tawbaware.com/film_digital.htm) [Film vs. Digital Cameras](http://www.kenrockwell.com/tech/filmdig.htm) [Film vs. Digital](http://www.ltlimagery.com/film_v_digital.html)