gettheetoabrewery

EDIT: I appear to have made a serious multiplication error in the first version of this post. While the figures for the actual detail of each film frame were correct, the scan resolutions were needlessly doubled. I have fixed this.

TL;DR: The upper limit on the detail to be seen on movie film is 4064 dpi for color film and 5080 dpi for black and white. However, to make certain that all the detail from a frame of said film is captured correctly by a digital scan, you need to at minimum scan color film at 5748 dpi and black-and-white film at 7185 dpi.

I’ve seen so many arguments online about how much detail motion picture film does or does not contain in terms of digital resolution. Never mind all the other factors that go into the look of a piece of film, or how “important” resolution actually is once you get to a certain threshold, people really want to know all about the megapixels. While the correct answer is going to vary by the exact type of stock used, the exact type of lens used, and the exact contents of the shot itself, I felt like it should surely be possible to calculate an upper limit, a best-case scenario, based on directly quantifiable factors. Yet I haven’t really seen anyone lay that out in simple terms in any of the aforementioned discussions. Here’s my attempt at a standard, copy-pastable response that gives exact figures while qualifying the nature of those figures.

Film is analog. It doesn’t have pixels. So what does it have? How do you express the smallest resolvable detail in a frame of film? You do so in “line pairs per millimeter” (as an example, picture the thinnest possible alternating white and black lines that can be captured by a camera while still being distinct instead of fuzzing into a grey mess). The highest lp/mm for motion picture film, which has a very hard limit to its exposure time (about 1/(2*X)th of a second, X being the framerate), seems to lie somewhere between 80 and 100 according to multiple sources written specifically for cinematographers. In particular, after investigating the tech specs of as many different movie film stocks as I could find, the highest lp/mm rating for color film was 80, while for black and white it was 100. These appear to be hard limits. [Cinematographers, please inform me if you’ve ever seen anything higher.]

HOWEVER, the probability of the average subject of a given shot being translated to the negative with that much detail given normal lighting, lenses, etc., then said detail being carried through an interpositive and the various stages of editing, is effectively nil. Reaching these hard limits in a final print would be almost impossible without specifically designing the shot as a boring test pattern, but the point is that it’s technically possible and thus serves as a usable ceiling for our calculations. With this kept in mind, let’s continue.

Alright, so with each of those “lines” (two to a pair) representing the smallest resolvable detail, we would naturally set them equal to a pixel-width on a given axis. So, the captured detail on film tops out at 160 pixels per millimeter for color and 200 pixels per millimeter for black and white. Since one inch is equal to exactly 25.4 millimeters, you can translate those figures into dots/pixels per inch for film scanner settings, ending up with 4064 dpi for color and 5080 dpi for black and white. So, that’s your answer, right? Yes and no. Yes, that’s the effective amount of resolvable detail the film can capture, but no, you can’t just scan it at that size and call it a day.

Converting continuous analog detail into discrete digital information isn’t a straightforward process, and doing a simple “one-to-one” conversion often results in aliasing of details. The Nyquist theorem states that capturing that continuous detail in a discrete form requires more than doubling its measured frequency (said frequency in this case being the line pairs per millimeter). So just double the line pairs and, as it works out, the Nyquist theorem is satisfied by the resolution provided by the individual lines, right? Close, but not quite. In film, the vertical and horizontal detail are both continuous, as opposed to other analog sources like VHS or LaserDisc, which have discrete vertical detail but continuous horizontal detail. The two axes aren’t a pair of independent lines, they make up a plane. As such, you have to deal with diagonal aliasing, so that diagonal frequency needs to be doubled as well. Skipping the Pythagorean math, the result is that in order to successfully capture all detail in a continuous 2D plane, the frequency (lp/mm) needs to be multiplied by a minimum of 2*sqrt(2), or about 2.828. In terms of the dpi on a film scanner, that comes out to minimums of 5748 dpi for color film and 7185 dpi for black and white film before you can be sure that all resolvable detail on the film might be captured properly in a digital format. Note that higher resolutions may be needed to eliminate all aliasing. These are very much minimum scan settings for that purpose. Downscales from this scan to the film’s “native” equivalent digital resolution image would be superior to a scan done at the “native” level to begin with.

So what does that mean for individual film gauges and the movies shot on them? Having perused the SMPTE standards for the exact measurements of camera apertures and demarcations for usable film area, I’ve prepared a pair of tables defining in exact terms the “detail resolution” (the equivalent digital resolution of the information on the film) and “scan resolution” (the digital resolution required to properly capture that information) for that type of film. The entry format is as follows:

• [Film gauge and type]: [resolution of entire exposed frame, AKA everything captured during filming], scan at min [resolution needed to capture all detail]
• –[Aspect ratio per unit] AR: [resolution of standardized picture area to be projected, AKA everything you’re supposed to see onscreen], on min scan [resolution of projected picture on aforementioned scan of frame]

A few last notes about the table. In more familiar terms: 8mm Type R is regular 8mm. 8mm Type S is Super 8. 16mm Type W is Super 16. 35mm’s Type A aperture is standard nonanamorphic, Type B aperture is standard anamorphic, Type C aperture is Super 35 four-perf, and Type D aperture is Super 35 three-perf. 65mm 8/70 format is the rarely-seen MagnaVision. 65mm 15/70 is what everyone calls “IMAX”. Some film types and aspect ratios do not have specified projectable areas from the SMPTE, which is why you don’t see them listed. Also, some of these numbers may be hypothetical: For example, I don’t think a MagnaVision project has ever used black and white film, and I don’t know if normal 8mm has ever used stock that was capable of up to 80 or 100 lp/mm. But such film could be custom made by the manufacturers using the same material if you pay through the nose for it, so I included them.

Color

• 8mm (Type R): 781x589, scan at min 1105x833
• –1.324:1 AR: 700x528, on min scan 989x747
• 8mm (Type S): 927x663, scan at min 1311x937
• –1.324:1 AR: 850x642, on min scan 1202x908
• 16mm: 1642x1199, scan at min 2322x1695
• –1.329:1 AR: 1545x1163, on min scan 2184x1644
• 16mm (Type W): 1976x1188, scan at min 2795x1679
• –1.662:1 AR: 1888x1136, on min scan 2671x1607
• –1.850:1 AR: 1888x1021, on min scan 2671x1444
• 35mm (Type A aperture): 3520x2560, scan at min 4979x3621
• –1.371:1 AR: 3354x2447, on min scan 4743x3460
• –1.661:1 AR: 3354x2020, on min scan 4743x2856
• –1.850:1 AR: 3354x1813, on min scan 4743x2564
• 35mm (Type B aperture): 3520x2975 w/ 2:1 squeeze, scan at min 4979x4207 w/ 2:1 PAR
• –2.391:1 AR: 3354x2805 w/ 2:1 squeeze, on min scan 4743x3967 w/ 2:1 PAR
• 35mm (Type C aperture): 3988x2988, scan at min 5639x4225
• 35mm (Type D aperture): 3988x2220, scan at min 5639x3139
• 65mm: 8397x3682, scan at min 11875x5207
• –2.197:1 AR: 7770x3536, on min scan 10988x5001
• 65mm (8/70 format): 8421x6036, scan at min 11909x8536
• –1.349:1 AR: 7770x5760, on min scan 10988x8146
• 65mm (15/70 format): 11266x8258, scan at min 15932x11679
• –1.433:1 AR: 11136x7770, on min scan 15749x10988

Black and White

• 8mm (Type R): 976x736, scan at min 1381x1041
• –1.324:1 AR: 874x660, on min scan 1237x934
• 8mm (Type S): 1158x828, scan at min 1638x1171
• –1.324:1 AR: 1062x802, on min scan 1502x1135
• 16mm: 2052x1498, scan at min 2902x2119
• –1.329:1 AR: 1931x1453, on min scan 2730x2055
• 16mm (Type W): 2470x1484, scan at min 3494x2099
• –1.662:1 AR: 2360x1420, on min scan 3338x2009
• –1.850:1 AR: 2360x1276, on min scan 3338x1805
• 35mm (Type A aperture): 4400x3200, scan at min 6223x4526
• –1.371:1 AR: 4192x3058, on min scan 5929x4325
• –1.661:1 AR: 4192x2524, on min scan 5929x3570
• –1.850:1 AR: 4192x2266, on min scan 5929x3205
• 35mm (Type B aperture): 4400x3718 w/ 2:1 squeeze, scan at min 6223x5259 w/ 2:1 PAR
• –2.391:1 AR: 4192x3506 w/ 2:1 squeeze, on min scan 5929x4959 w/ 2:1 PAR
• 35mm (Type C aperture): 4984x3734, scan at min 7049x5281
• 35mm (Type D aperture): 4984x2774, scan at min 7049x3924
• 65mm: 10496x4602, scan at min 14844x6509
• –2.197:1 AR: 9712x4420, on min scan 13735x6251
• 65mm (8/70 format): 10526x7544, scan at min 14887x10669
• –1.349:1 AR: 9712x7200, on min scan 13735x10183
• 65mm (15/70 format): 14082x10322, scan at min 19915x14598
• –1.433:1 AR: 13920x9712, on min scan 19686x13735