# How many pixels in an 8x10 neg?

Discussion in 'Large Format' started by bill_youmans, Oct 3, 2000.

1. ### bill_youmans

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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2. ### huw_evans|3

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.

3. ### shambrick007

"rendering images equal to any film-based effort. "<p> Yeah, but I'm
sure they weren't considering LF...as most people don't.

4. ### chris_werner|2

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. ;-)

5. ### jnorman|1

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...)

6. ### zoom

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

7. ### pete_andrews

Juggling numbers doesn't actually tell us very much about image quality.
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.
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 really closer to showing a truly analogue tone scale; film grain, or pixels?
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 appears to be smoother in tone than the print. The regular matrix of pixels gives a better impression of truly continuous tone than film grain.
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.
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.
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.
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 does matter.) It's only 6 megapixels, but this is well in excess of the 2.5 mp/sq. inch that I mentioned earlier.
I think quite a few eyebrows are going to be raised by it.
Leaf, LightPhase, and the rest should start worrying about their future.

8. ### john_henderson|1

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.

9. ### ron_shaw

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

10. ### steve_swinehart

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.

11. ### ron_shaw

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.

12. ### matt_oulman

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
Digital is to film what video tape is to film. Imagine video tape on a
70 foot theater screen.

13. ### pete_andrews

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.
The use of crude black and white bar test patterns tells us absolutely nothing about the percieved quality of an imaging system except its ability to pass crude resolution tests.
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?

14. ### steve_swinehart

"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
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.

15. ### ron_shaw

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).

16. ### steve_swinehart

I've checked out their website, and I stand by my statement that
their methodology is flawed.

17. ### ron_shaw

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.

18. ### david|4

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

19. ### david|4

The web page is
ME%20PAGE%20

20. ### greg_lawhon

David:

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