How many pixels in an 8x10 neg?

A coffee break discussion prompted the following question:

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How many pixels would a file contain if an 8x10 digital back were available (color or B/W)?

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Seems there was a National Public Radio story that a consumer camera available in 2001 will have a 10 megapixel chip as standard equipment, rendering images equal to any film-based effort. I was arguing that in a 1/15th of a second, an 8x10 piece of film can collect huge amounts of "pixel" information, probably dwarfing 10 megapixels. Anybody know?

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Thanks in advance - Bill

Well, here's my rough answer: in round figure an 8x10 negative is

about 200x250 mm. If we say that a good B&W film is capable of

resolving well over 100lpm (again, just round figures), then you need

at least 200 pixels per mm. LF lenses won't match that resolution, but

you'll still need it to replicate the tonal gradation.

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That gives 200x200x250x200 = 2 billion pixels. That is 200 times the

size of that 10Mpixel chip, and that is almost certainly an

underestimate!

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Not only that, but I think I'm right in saying that each pixel uses

several bytes for 24-bit colour rendition, and it's clear that for an

uncompressed image you will need several GigaBytes of storage. I hate

to think what the power supply would be like.

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So, if my arithmetic is right, and you're planning that week-long

photographic trip into the backwoods with current digital technology,

you'd better hire half a dozen pack mules and a portable generator!

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Huw Evans.

"rendering images equal to any film-based effort. "<p> Yeah, but I'm

sure they weren't considering LF...as most people don't.

Huw,

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You're right about color rendition - that requires a minimum of 3

pixels (R, G, B). 24 bit color likely requires more, but this is

beyond my specific knowledge.

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I think I also recall that a 35mm negative contains roughly 25-30

megapixels of data, but don't quote me on that. If right, though,

digital is still a long ways away from a mano a mano quality

comparison with film at any format. I wonder when the dramatic

improvements we have seen in digital will run out of gas in the face

of practical limitations on miniturization, and whether this will be

before or after digital exceeds chemistry in data storage capacity.

It's easy to say now that digital will ultimately win out, but I

question whether it's really that simple (see the human brain).

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Wow, I fell into an unanticipated philosophical twist. ;-)

we can also look at this from the other end. it requires about

300dpi to achieve truly visually-satisfying reproduction (print)

quality (for example, the reproductions in a high-quality fine art

book). 300 x 10" = 3000 pixels across, 300 x 8" = 2400 pixels high -

that translates to 7.2 million pixels. at 24-bit resolution, that is

about 173MB file size. at 600dpi (to allow for 16x20 enlargements

for exhibition purposes), you would be looking at file sizes of about

690MB. this level of image quality is within the capability of

existing technology (well, i admit you need a lot of RAM), and i

would guess variations of it will be common in the near future. on

the downside, if kodak wont even make a b/w film in 4x5 readyload

anymore because the market is too small, who in the world do you

think will manufacture an 8x10 digital back? (i wonder how long it

will be before the LOC accepts any form of digital imaging - digital

files, digital prints, and/or digitally printed "negatives" or some

other form of hard-copy "original", as part of its archival

collections...)

I have done some experiments digitising film to see what you can get

out of it and does appear that the limiting factor is lens technology.

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You can see the grain in Provia F at about 6000 dpi but above 3-4000

dpi the lenses I have used have not provided any more information.

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At 3000 dpi this produces a 720 MegaPixel image (2 GBytes (24 bit)).

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If you are interested the results of scans at 1600, 3000, 6000 and

12,000 dpi they are at:-

http://193.113.131.213/pg/dpi/?lf2

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Viewing the images requires your browser to run a Java applet. I will

have a none java system by the end of the month.

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Regards

Juggling numbers doesn't actually tell us very much about image

quality.<br>If you consider the fact that every grain in a film can

only be 'on' or 'off', i.e. developed on not, then film itself is very

much a digital medium.<br>Now consider the nature of a pixel: Sure, it

covers a much larger area than a film grain, but it's also capable of

showing a whole gamut of brightness levels, from absolute black to

pure white. Which is <i>really</i> closer to showing a truly analogue

tone scale; film grain, or pixels?<p>The way that the human eye sees

things must also be taken into consideration. The eye accepts regular

patterns of dots as a continuous tone, much more readily than it

accepts the random scattering you get with film grain. A coarse

grained photographic print has many more grains per inch than a good

133 to 200 screen magazine or book illustration, but the book

illustration <i>appears</i> to be smoother in tone than the print.

The regular matrix of pixels gives a better impression of truly

continuous tone than film grain.<br>IMHO comparing film directly with

a digital image, on a purely numerical basis, is like comparing apples

with bananas, but if you want some numbers, I think we ought to start

with the human eye.<br>The eye can resolve at best about 8 lppm at

normal reading distance. Even if you increase this to 10 lppm or 20

pixels/mm, this only works out to 82 megapixels to cover a 20" x 16"

print. The final viewing size is much more important than the negative

or film size.<br>Or, if you want the hypothetical equivalent of film:

We'd need at least 255 film grains to show the same tonal range as a

single pixel, and this involves a film area equivalent to at least a

16 micron square pixel. (The pixels in consumer digicams are about 5

microns square BTW). This is about 2.5 megapixels/square inch; you

work out the numbers, they're far lower than the gigapixels that have

been bandied about previously.<p>Anyway, wait until we've seen the

results from the new full 35mm frame-sized CCD camera announced at

Photokina. (At last the

digital design boys have realised that size <i>does</i> matter.)

It's only 6 megapixels, but this is well in excess of the 2.5

mp/sq. inch that I mentioned earlier.<br>I

think quite a few eyebrows are going to be raised by it.<br>Leaf,

LightPhase, and the rest should start worrying about their future.

Hmmmm....I've often estimated this myself, and usually come up with

about the same number - 4000 dpi. The Kodak DCS-660, with 3Mx2M

array, would need to have twice the linear resolution to confidently

capture the detail in a 35mm negative (were the array 36mm x 24mm,

which it is not).

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The 100 l/mm number would require 200 pixels/mm minimum. (In signal

processing, we call this 2x point the Nyquist sampling rate.) This

already gives over 5000 dpi. In practical signal processing, we'd

oversample somewhat. I could even argue that 4 pixels/line pair were

required. (For those who can visualize it, imagine sampling a square

wave right at the transitions - you'd get no variation.)

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I usually start this mental exercise with about 50 l/mm to compare

with 35mm film, so my "required" resolution is less than what I just

showed.

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Any way you slice it, you find that the VERY EXPENSIVE,

top-of-the-line sensors today aren't close to capturing the

information that film can.

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You can follow the "300 dpi for print" rules and come up with smaller

numbers. Of course, when you choose a resolution, you have to know

how big your biggest enlargment or cropping will ever be. I'm a

proponent of capturing all you can when you take the picture. It's

kind of like cropping. If you take too much image (too much

information) when you take the picture, you can crop. Likewise, if

you take too many pixels, you can always downsample.

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OK. I want to blather on more, but I'll stop now.

Check this site

for a comparison

of various

digital cameras

to each other,

and to 35mm Kodak

E100 slide film.

It seems that the

6MP imager used

in the Kodak 660

and the Phase One

med. format back

(also using the

6MP imager)

captures more

detail than 35mm

film. Very

interesting! http://www.imagingspectrum.com/portraitcomparison.htm

Don't really think you can come to that conclusion from

these "tests." The type of digitizing for the film, compression for

display etc. don't give a true method of comparing detail. Plus the

digital pictures were "sharpened" with software giving a bias towards

appearing to have more detail.

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The only way you could really make a comparison is to use a lens

resolution chart, enlarge the film onto paper to show the area with

the most discernable line pairs per millimeter, and then perform the

same test for the digital camera with output to a Lightjet or like

printer with no software manipulations to the digital file. This

isn't a real test as there were no controls applied to the process.

It's only a sloppy presentation of some comparisons masquerading as

information.

Sharpening wont create detail that isnt in the file. I didnt say

sharper (but they are), but do indeed contain more detail. Like it or

not, digital is coming of age. Digital solutions for LF are taking

over studio work by the droves. Pros who make thier living with the

images they create are finding that digital is making that easier. See

how you feel about digital imaging in another 5 years.

Everyone seems to like to say 600 dpi is the starting point.

But realistically 600 dpi will not give you a "photo quality image"

when printed. It takes at least 1200 dpi to print an acceptable

"print". So you can double all the numbers you favor.

But it doesn't matter to me in the least if digital is comparable to,

or exceeds the "clarity" of film.

Photography is a craft unto itself. I view it much the same as any

other - the results are more often treasured for their artistic value

and the appreciation of the artisanship that went into the final

product.

I think of the comparison as being similar to mass production. Why

would anyone want hand-built, solid oak furniture made by a talented

craftsman when they can buy a mass-produced, particle board/veneered

piece at half the price? Which is most appreciated, and which will be

treasured for decades or longer?

Digital is to film what video tape is to film. Imagine video tape on a

70 foot theater screen.

No need to imagine videotape on a 70 foot screen, you can go and see

it, practically anywhere, because movie theatres are rapidly moving

towards all digital distribution.<p>The use of crude black and white

bar test patterns tells us absolutely nothing about the percieved

<i>quality</i> of an imaging system except its ability to pass crude

resolution tests.<br>Waving figures of 300, 600, and 1200dpi about is

meaningless, unless you tell us the context. Is that on film, in a

scanner, in a final print, or what? Is that a dye-sub or light-jet

print, or a crappy fixed-dot-size ink-jet?

"Sharpening wont create detail that isnt in the file. I didnt say

sharper (but they are), but do indeed contain more detail."

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While that is true, the sharpened image will have the visual

appearance of being sharper which gives the illusion of more detail.

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The problem with the comparisons is that the test methodology used is

flawed.

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1. We do not know the amount of magnification of the images.

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2. The film was digitized. This alone negates the entire comparison

process. We do not know if number of pixels it was digitized at was

appropriate for the amount of magnification. Further, we do not know

if the film scan captured the maximum resolution of the film! Hence

the need to use a fixed, know target such as a lens resolution chart

instead of an aribitrary comparison of a portrait.

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For example, while I might get away with 3000 ppi scan for an 8x10

from 35mm, if I want to go to a 48 inch wide print, I will have to

have the film digitized at about 11,000 ppi. The same holds true for

examining small areas of film to look for details after it has been

digitized as this is, in effect, an enlargement,

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3. The only way to compare the true resolution capabilities is

through controlled tests of the entire imaging "system," and not

through poorly thought out comparisons.

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As to your comment, "See how you feel about digital imaging in

another 5 years."

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I feel fine about digital imaging. I use it daily. I've had papers

published by the Society of Photo-optical Instrumentation Engineers

on image processing of digitized infrared video. I also use digital

imaging in my personal photographic work. I just don't to buy into a

presentation that is really pseudo-photoscience.

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I test video equipment for resolution, imaging, dynamic range etc.

with image quality evaluated before and after digitizing. From my

perspective, the tests were not setup and carried out correctly as

the total imaging systems (digital and photographic) were not

compared equally because of the test methodology used.

Steve, you apparently did not check out the url. They give all

details of the images, and the scanning resolution (5700 DPI) on an

Imacon Precision II Film Scanner. You can see the grain (or dye

clouds) in the scanned film image. Some of the skin texture is

obscured by the grain in the scanned film image, not in the Phase One

image. This is also an old CCD (at least 5 years old). They also give

the magnification (in equivalent print sizes, both 11x16 size, and

16x24 size).

I've checked out their website, and I stand by my statement that

their methodology is flawed.

These images were not printed. These are the image files, so printing

has nothing to do with it. As far as scanning the film, if enough

resolution was used to reveal the dye clouds, I dont see what a

further increase in scanning resolution has to do with it, as the

resolution used shows the limits of the film. Regardless

of your opinion of the methology, I find the results interresting, and

speaks a lot for the state of digital imaging, especially considering

it is still in its infancy. Check out the images on the Hasselblad web

site from thier new digital camera (at only 4MP, the images are

superb). It will be interresting to see the images from Kodaks new

16MP imager due out early next year.

Check out the website of Foveon, Inc. of Santa Clara, CA. It shows an

8 foot (96 inch) tall photograph captured with a 35 mm version of the

16 megapixel sensor chip. It will blow your mind. Hassleblad will be

making MF camera with an enlarged version of this ch

The web page is

http://aolsearch.aol.com/dirsearch.adp?knf=1&query=large%20formAT%20HO

ME%20PAGE%20

David:

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That URL didn't work for me. This one did: www.foveon.net