Brad Templeton: How many pixels are there in a frame of 35mm film.pdf

8/14/2019 Brad Templeton: How many pixels are there in a frame of 35mm film.pdf

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eye as a 35mm shot, except when blown up very large and looked at quite closely.

It's important to note another key difference. Film, as an analog medium, does not record just 256 grayscales

or the corresponding 16 million colours. And film scanners, even doing just 8 bits per colour, get 24 bits of data

for every single pixel. Today's digital cameras only get 8-12 bits of data for each pixel and they guess

(interpolate) the other 16. So the colour accuracy for even a scanned film image is better than the modern

digital camera. Good film scanners can also extract more than just levels from 0 to 255. They can often go to12 bits (0 to 4097) to detect much more detail in shadows, and provide more contrast. As such a film scanner

gets as much as 36 bits of information for each pixel, instead of 8.

More modern digital cameras gather 10 or even 12 bits of the single colour pixel, and keep it if they record in

RAW mode, but reduce it in JPEG mode. Foveon digital cameras record all 3 colours per pixel, like film, but

their sensors have lower resolution as of now.

As a counter note, the 24 bits of colour from a film scanner, while better than the 8 to 12 bits per sample of a

bayer-interpolated digital camera, is nowhere near near 3 times as good as some pretend. The interpolation

algorithms are good, and rely on the fact that to the eye, particularly in natural scenes, position-brightnessinformation is much more important than colour information. How much better full colour information is is

subjective, but it's not even close to 3 times better. On the other hand, even the 36 bits from the best scanner

is not enough. The film has more information.

Negative film itself tends to be able to hold around 1000 to 1 contrast range. Quality slide film projects more

levels, though over a slightly narrower exposure range. (To make this clearer, negative films capture a wider

range but can't display it when printed. Slide films capture a more narrow range, just a bit better than digital,

but can display it all when projected.) Generally one desires at least 12 bits per colour to represent it. Your

eye, by widening and closing the iris, can sample an astounding (eye-popping!) 7 decimal orders of magnitudeof range of contrast, which would need at least 24 bits.

So there is a lot of information in film. However, not all of it is usable information, which causes the debate

about the equivalence in pixels. Film is made up of chemical grains or dye clouds. The more you blow up film,

the more you start seeing noise caused by those grains, and eventually the very clumping of the grains

themselves. Of course some are bothered by the grain more than others.

The finest films (which are slow and best with sunlight or flash) have very fine grain, and in many cases, the

limits of the lenses blur the image before the grains start causing too much trouble. However with a decent

lens you don't have to blow up too much before you see the grain. The better digital cameras are also starting

How many pixels are there in a frame of 35mm film? http://pic.templetons.com/brad/photo/pixels.html

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to exceed the quality of most zooms and even some prime lenses.

These films, with good lenses, are capable of resolving as much as 7000 pixels (3500 "line pairs") over the

width of a 35mm frame -- about 5000 dots per inch. However, before that point, while they can resolve "line

pairs," the image is pretty noisy. The lines are not resolved as straight, sharp-edged entities, but you can tell

there is a white line next to a black line.

There is more information to be extracted even at this fine resolution, but the deeper you go, the more noise

you also extract.

To make the image not look "grainy" and otherwise poor, you need to pull back. Subjective tests suggest this is

to about 4000 DPI, or around 5600 pixels. For a 3:2 frame, that means around 20 million pixels. (Of course

some people don't mind grain as much as others, so your mileage may vary. Also, if you can get a scan that

good, digital techniques can reduce the visibility of grain and extend the resolution of film.)

Down at this level, however, you're reaching the limits of most lenses. They may be able to resolve

high-contrast items at this level but most pixels are a little blurry. A crop at this level does not look nearly asgood as a scaled down full shot.

What this means is that a 5300 x 4000 digital camera can produce a shot equivalent to a scan from a quality

35mm camera -- provided you could get more than 8 bits per pixel. You could blow up the 35mm shot a little

bit more and see a little bit more, but only at the cost of producing a grainy image. Chances are a 3000 x 2000

digital camera would match the 35mm for a good percentage of shots.

Prints

Prints also are analog output. In theory a print can have all the information of film, however photographic

paper tends to only be able to hold a range of 100 to 1 in contrast. That's less than a monitor can. In addition,

the printing process is not perfect, and often blurs an image. Typical lab prints don't seem to store much more

than 200-250 pixels for each inch. Quality labs can do better -- perhaps up to 500 pixels/inch. (The paper can,

in theory, do more, but there isn't that much more in the negative.) Thus a 5x7 print probably is similar to a

1400 x 1000 digital image (if the digital image has enough bits per pixel.) It's rarely more than the 2100 x

1500 that 300 dpi would imply.


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It's always better to scan from print film or slide film. You get far more contrast, and far more detail, and it's

not second generation. (Though be warned some slide scanners are not up to the range of contrast in a good

slide.)

Digital PrintingMakers of digital printers play lots of games with their resolution. The "dots" they speak of (when they talk

about a 720 dpi resolution) are dots of single colour ink. A pixel, on the other hand, is a dot capable of the full

colour range. You need lots of dots to make a specific colour and not look spotty. To render a pixel well can

require scores of ink dots. In the end, the goal is a "continuous tone" image at a given number of pixels per

inch. Most printers can only simulate continuous or near-continuous tone. (Digital film recorders, or

photographic paper recorders, can do near-continuous tone.)

Getting the scan

Today, high end digital SLRS commonly have over 20 megapixels. Serious shooters are preferring them to film.

First of all, the resolution is pretty similar to film at its best, and secondly getting everything out of film

requires a lot of work with a very good scanner.

Scanning is hard work. One must deal with dust and fingerprints. It takes a lot of time. And it adds another

generation to the process, dependent on the optics and scanning elements of the scanner.

Pixel-Mania

Today in digital cameras, marketing departments have created a bit of pixel-mania. They are working too hard

at increasing the number of megapixels they can advertise without always caring about the quality of the

pixels. A small point and shoot with 8 megapixels is probably a lot worse than the old 6 megapixel canon D60

-- it may even be worse due to noise that the 3 megapixel D30. Resolution is important but not the only thing.


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What would you rather shoot on?

The real question of course is "which do you want to shoot on?" When considering the quality DSLRs from

Canon or Nikon, most people switched to preferring the images from the 8 megapixel models compared to

35mm film, and very few are unsatisfied with the 20 megapixel models. In fact, they are competing in someminds with medium format shooting.

Can they get a better shot with a 120 chrome than an 20MP DSLR? Probably, but only by a modest amount.

But the DSLR is just so much easier to work with, and so much more flexible that when the final goal is digital

(as it almost always is today) the choice for these photographers is not very hard.

Other Issues

You may want to look at my set of 35mm photos current digital cameras can't shoot.

You can read about the tradeoffs between digital and 35mm.

Check out my pages of Panoramic Photography, the marriage of digital and film.

If you have bought a new Canon DSLR, check my page on what lenses to get for a DSLRor what camera to

buy at all.


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Brad Templeton: How many pixels are there in a frame of 35mm film.pdf