How many MP (GP) is an 8X10 equivalent to?

[Brian Vuillemenot]

Hello all,

The recent post about the scanning back for 8X10 and the 1 gigapixel Bryce Canyon image got me wondering how many maga pixels a 4X5 and 8X10 transparency would be equivalent to. I know that film grains are not equivalent to pixels, so it is not directly comparable, and it would obviously vary depending on film. Let's just say, how many mega pixels would a camera have to deliver to match the resolution of 4X5 and 8X10 Velvia(the old iso 50)? I had heard one statistic of 400 MP to match an 8X10 transparency. Any one have any ideas? Thanks!

[Bruce Watson]

In general, you can retrieve just about all the information captured by a photographic film by scanning around 4000 ppi. Clearly, this number must vary based on the film and it's internal structure. You can get into religious wars debating this stuff, and whether negative film is sharper than tranny film, etc. and I'm not going there with anyone.

Basically, pick a number you like. Then do the math:

(4000 ppi)(4 in)(4000 ppi)(5 in) = 320 Mpixels.

(4000 ppi)(8 in)(4000 ppi)(10 in) = 1280 Mpixels.

A low grain high resolution film like Velvia probably can be scanned at even higher scanner resolution to good effect. Therefore, IMHO, your estimate of 400 Mp for an 8x10 tranny is quite low. Of course, YMMV.

[Bill_1856]

Great question. Now, let's see if anyone actually gives a straight answer.

[QT Luong]

I would think that to capture all the information on film, you would need 5000dpi. This is the standard scanning resolution offered by Wci for scanning 35mm.

One has to keep in mind that the pixels obtained from scanning film are quite grainy/noisy compared to those obtained with digital capture. Because of that, while a 4000dpi scan from 35mm has more than 20 Mp, almost everybody agrees that a 11 Mp image direct from a 1Ds camera is superior. Apparently a lot of people even prefer a direct 6 Mp image, although clearly the resolution is less.

[Frank Petronio]

You can scan as high as your scanner's resolution will go. A Linocolor Tango will easily produce a 2 gig file from an 8x10, and I don't see why you couldn't go to 4 gig with Mac OSX. Whether you could do anything practical with a 4 gig image file is quite another thing. FWIW, I just produced a 14 x 44 foot billboard - they print these at 9 dpi (not a typo) - so the stuff you see on the highway is never more than 50 mb. There isn't much point in going for higher and higher resolutions if you know what your final output is going to be. Even if you're Thomas Struth or Richard Avedon, and want to print expensive 8 foot tall custom prints, a 4 gig image would be way overkill (and quite a slog to RIP.)

Straight answer - a gig scan of an 8x10 should cover all your potential needs and then some. Most people agree that 35mm scans of 50-60 mb are the max, and 8x10 is simply 20 35mm slides tightly packed. 20 x 50mb = 1 gig.

[Marc Genevrier]

The fact that scanning with 4000 dpi captures all information that is present on the film doesn't mean that so many information is really there, especially as you go to greater formats. A 35mm slide may contain as much as 3000 dpi, but a MF slide will much probably contain only 2500 dpi or less, a 4x5 would be 1800 dpi and 8x10 1200 dpi (don't pay too much attention to the values, this is just to illustrate my argument).

Hence, I would suggest another approach. The question is: how many line pairs/mm (lpm) do we have on our slides? Let us say 30 lpm for 8x10 (and I'm not even sure that we always get so many). One line pair is equivalent to two pixels (one black, one white in a simplified model). Hence, the total number of pixels: (pixel count in the length x pixel count in the height of the slide) (one inch=25,4 mm) (30x2x10x25,4)x(30x2x8x25,4) = 185 MegaPixels

Take any value you want for the resolution on your particular film and you will obtain a different count. As for myself, I would say that a standard 8x10 is around 100 MPix. By the way, I recently read an ad' for a 120 MPix scanning digital back that says that the resulting image contains more information that a 8x10 slide...

[Bill_1856]

How much detail one can get from a scanned transparency is avoiding the point. The question is how many megabites from a digital camera does it take to show the same amount of detail that one can see (with suitable magnification) on a 4x5 or 8x10 Velvia transparency.

[QT Luong]

Bill, multiply the ratio of surface areas to 35mm (which is about 15 for 4x5 and 60 for 8x10) by the number of pixels in a digital camera that you think matches 35mm film (something between 5mp and 11mp). For 8x10, by this calculation, the low estimate would be 300 megapixels. Color file size is 3x number of pixels (one byte each for RGB). This doesn't take into account possible loss in the 8x10 due to lens diffraction limits, film imperfect flatness, etc...

[Ellis Vener]

What size are you going to print to? Up to at least 16"x20" a 16 to 22 MP ( kodak, leaf valeo, imacon) back will at least equal the amount of detail you can get out of 4x5 transparency like Astia 100F, which has more resolution than RVP. If you think I'm wrong, prove it and not with calucations but with images.

[QT Luong]

Ellis, up to at least 0.1" x 0.15" a desktop webcam (logitech, apple, ...) will equal the amount of detail you can get out of 4x5 transparency like Astia 100F, which has more resolution than RVP :-).