Buyer's Guide: 8mm Movie Film, Super 8 Film, and 16mm movie film to digital video Tutorial.
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Concepts and terminology of movie film to video and/or DVD
Resolution
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By: Bruce Mayfield |
A fundamental concept in all imagery science, is "detail resolution" (hereafter called "resolution"). In effect, resolution is visual information or visual data that makes up an image. The more information you have, in an image, the more detail you can actually see. The more data you can see, the more realistic -- true to life -- the image appears. When both 1) measuring and 2) talking about resolution, "more" (i.e., "higher") resolution is better. The "higher" the resolution, the better the image looks.
In the movie film world, taking two pictures of the same object, a larger piece of movie film (i.e., 35mm slide film) has more "resolution" than a smaller piece of film (i.e., 8mm movie film). When comparing the movie film world to the HDTV world, movie film -- Standard 8mm, Super 8 -- is worse than HDTV. This can also be argued to be true for most of the Silent 16mm movie film of the first half of the last century --as silver in the movie film was "milled" by mechanical processes. Chemical manufacturing processes - latter century -- changed the validity of that argument.
In the analog and digital world (your TV set or HDTV screen respectively), resolution is measured in "lines of resolution". There are "vertical lines of resolution" and "horizontal lines of resolution". In the digital world, resolution is measured in "dots or pixels per inch". Dots or pixels per inch are expressed -- for the vertical and horizontal axis of the display device, too.
To illustrate a layman's discussion of "resolution" -- so even Grandma & Grandpa can understand it:
- We will assume that "lines of pixels" and "lines of resolution" are
the same. (They are not*)
(for more information, see tech notes below) - We will assume that "dots" and "pixels" are the same. (They are not.**)
- We will assume that "dots" and the "grains" in your movie film are the same. (They are not.***)
To get a basic feel for resolution as it relates to video: HDTV has display resolutions of 1,280×720 pixels (720p) or 1,920×1,080 pixels (1080i/1080p). If you're in North America, your (old) television set's picture is NTSC and has an effective resolution of 525 pixels by 480 pixels (Picture Element, or one dot of the image).
Digital "resolution" is determined by the "source data" (Mama's picture) arranged as a "logical matrix" (i.e., a two dimensional data array). The true resolution of the image is determined by the rows and columns of information. You could think of a digital image as a spreadsheet -- with each cell of the spreadsheet containing a chunk of visual information to be displayed -- not the physical matrix of pixels in the screen. To put it simply, a matrix of visual data (one frame of Mama's image reduced to ones and zeros) is re-computed, mathematically, to fill a matrix of pixels. If there are more pixels in the display device, than there is digital data, then the display device averages or even doubles pixel activity to blend the actual visual data over the given physical space that must be filled. The fancy word for all this visual "slight of hand" is called "decompression" -- "or up-scaling or down-scaling -- depending if you are going "up-scale" to HDTV or "down-scale" to an iPhone or iPod. For simplicity, let's stick with the term, "decompression"..
Most people think of a "line of pixels" and a "line of resolution" as the same.
| Dirty Little Trade Secret™ |
| Beware the example images being shown to you! Too often you'll be shown a gorgeous frame of movie film as an example of film transfer prowess - but it will have been taken from a 35mm film frame and shown at twice the resolution of any digital video media offered. Read carefully! |
Movie film, even Standard 8mm movie film, is fairly high resolution. It is difficult to get a good comparison between movie film and digital image resolution since the silver halide crystal clusters (grain) not only vary in position but also vary in size -- depending on the "speed" of the original movie film and the method of processing. For the sake of simplicity we'll make some assumptions for our hypothetical piece of movie film. It will be a slow outdoor movie film with 90 lp/mm (line-pairs per millimeter) and it will be Super 8mm movie film with a frame size of 5.6mm by 4.1mm - yielding 756 by 553 "resolution" after we average the line pairs for variance in the grain.
So HDTV television signals are higher resolution than Super 8mm movie film - this is important! Keep this in mind when considering your movie film film transfer options.
Compression
Digital video -- of all flavors -- uses compression of some sort. It's necessary to get the information to fit on available media, as a truly raw high-resolution digital stream can take as much as 94 gigabytes (one billion bytes) of space for every hour of video - and that's without sound.
Two basic classes of compression are available: Lossless and Lossy.
Lossless makes for magnificent video - but to use it you need 1) vast amounts of very fast storage and 2) you can't compress it to much more than 85% of the raw stream size. Lossless formats are used by professional editors and broadcast studios. Equipment that uses this type of format is very expensive and is generally not economical for private use.
Lossy compression is much more common and easier to make use of. Some methods can manage as small as 15% of original stream size - but you wouldn't want to watch it. That level of compression is typically reserved for squeezing a little video over old analog modems. For most applications compression is kept in the vicinity of 40% to 60% of original size. The good methods let you use that level of space-saving while leaving you with a visually clear picture - though often the tricks used to achieve this come with costs down the line.
MPEG2, MPEG4, AVCHD formats used to compress SD and HD video onto a DVD, are VERY lossy forms of compression. These formats compress the images in a video stream two ways. First, it takes a key-frame and compresses it in a way similar to JPEG - averaging out areas of very similar colors and throwing away a certain amount of contrast information. Second, it does the same to the frames following the key frame, but then throws away any part of this new "delta frame" that isn't significantly different from the preceding image.
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| Why does this frame "look funny"? A JPEG image of a frame of highly compressed MPEG2 video. We over compressed this frame to show you what compression looks like -- if you zoom into a picture. This compression is the reason you can not blow-up MPEG2 frame, like you can a MiniDV frame. Once data is lost due to compression, it is lost forever. Still want to use a DVD to archive your home movies? |
This allows for a very high rate of compression while still keeping the image quite clear. it has its drawbacks, like any other form of compression. The most visible being the occasional visible line around the delta frame's "patch" of the preceding frame. Someone skilled in using this compression technique knows how to balance between visual quality and space saving, avoiding the risk of these ugly and distracting digital artifacts. The great movie filmmakers of the world employ skilled people for that very reason, which is why you almost never hear about or see those artifacts. Almost never.
DV Compression uses only a "lite" version of key-frame compression. DV does not use delta frames. DV (Same as MiniDV) has a bit stream of 25 Mbps (Megabits per second) or about 26 gigabytes per 2 hours of video with sound. This is the same for HDV, which also uses MiniDV tape. MiniDV is still used for acquiring footage for professional broadcast because it works well with hardware that "up-scales" for HDTV.
In comparison, MPEG2 on DVD averages about 5 Mbps or about 4.7 gigabytes for two hours of video -- when you're talking about DVD-R/+R in SP mode.
The result, with DV or MiniDV, is a stream of greater clarity with no visible artifacts (assuming nothing interferes with the encoding).
| Dirty Little Trade Secret™ |
| Because DVDs make use of the MPEG2
and AVCHD compression techniques -- which are profoundly
inferior editing formats; and, because DVDs only last only 2 to 5 years,
DVDs are valueless for archiving your family
memories.
For this reason, some "Super 8mm Film Transfer Mills™" (ethically?) will give you the option of "getting a MiniDV" made from your DVDs. This offer of an "optional MiniDV" should be a "RED FLAG" for you to run! What they don't tell you, is that they "copy" decompressed video from MPEG2 or AVCHD files -- either from your DVD or from their hard drive -- onto your MiniDV tape. That's right, they make your MiniDV from your DVD. To add insult to injury, many "Super 8mm Film Transfer Mills™" convert their video to analogue and then let a MiniDV camcorder re-digitize the video images -- yet again. Film transfer mills skillfully avoid calling your MiniDV a "digital master" -- which it is NOT -- when created from a DVD. They can NOT say your MiniDV is the "digital equivalent" of your original movie film, because most of your original movie film image was lost in making the DVD -- as a "synchronous" step in making your MiniDV. Their MiniDV is a "by-product" of your DVD. |
The DV compression method is the preferred method for use in editing digital video for experienced amateurs, "prosumers" and professionals working with smaller formats because the full-frame technique means you can cut, splice and re-arrange frames without risking re-building a key-frame from a series of delta frames -- like you do with AVCHD, MPEG2, and MPEG4. Every time this is done using AVCHD, MPEG2, and MPEG4, the artifacts from the delta frame patch are preserved and amplified, degrading the image quality.
There are a broad range of other lossy digital video compression methods out there - DivX, XviD, MPG4, Sorenson3, and WMV9, are some of the more popular among many others - but can be difficult to find or use if you're not an enthusiast or professional. They all have their drawbacks and strengths as well, and the variation of quality between these techniques is sometimes astonishing. This is important to keep in mind when choosing a film transfer technique for your movie film.
Lossless compression techniques like Black Magic's and FRAPS are rare and can be difficult to come by if you're not in the business of video editing. This is also important to keep in mind when choosing a film transfer technique.
Now that you know something about how to compress the video stream to fit media, lets have a look at the various forms of media out there.
TECHNICAL NOTES:
*1) Obviously, the assumption that "lines of pixels" equates to "lines of resolution", is technically incorrect. Resolution itself, can be expressed as a mathematical model -- simulated (simplistically) in a 4-dimentional data array -- wherein each dimension of each "dot" is expressed as 1) horizontal position, 2) vertical position, 3) RGB color pixel, 4) pixel intensity. After coordinates, and RGB color mix have computed, they are displayed in each "tri-dot matrix" on a 2-dimentional RGB field.
To add another level of complexity to this algorithm, in the TV world, only the odd, or else the even rows, of both the data array and the color matrix are displayed at any one given time. This is called, "interlaced display". In the computer world the rows can be displayed either as interlaced or all rows at once -- called progressive scan.
Want more complexity? In reality, a monitor can have more lines of pixels than the data array has lines of resolution; however, no monitor can have more lines of resolution than it has lines of pixels. When the number of pixels exceeds the corresponding number of "points of resolution", pixels are illuminated, according to a "cheating algorithm" whereby the pixels are averaged or doubled as needed to approximate the true "points of resolution". This "digital cheating" is what has generated and perpetuated the "big screen TV" market.
Yes, this technical explanation of resolution is still flawed, however, it does conceptually address the concept of resolution.
**2) In the black & white (B&W) technology, one pixel = one dot. Thus the public throws around the terms "dots" and "pixels" with little distinction. However, In the color world, one "dot" can be correctly argued to be made up of 3 pixels each -- Red, Green, and Blue. In color theory, varying the intensity of all 3 color pixels each -- from 0 to 255, or 256 intensities -- each dot has the potential of (256 x 256 x 256) 16,777,216 colors per dot. To explain resolution concepts, which are not related to color, we will use the terms interchangeably -- with preference given to the term "dot". Oh, by the way, aren't pixels little "dots"?
***3) Granules of silver halide -- the little specks you see in movie film images -- physically make up the image in your movie film -- just like "dots" in a newspaper photo. The size of these grains, or dots, determines the resolution of your movie film. Resolution, in the movie film world, is a moving target at best. Low light movie film (i.e., ASA 400) has much larger grains that daylight movie film (i.e., ASA 100). Also, the processing method (i.e., time in chemical baths and rinsing baths) to develop the movie film determines the density of silver halide partials left in the movie film. Also, the age of your movie film determines resolution. Movie film closer to the beginning of the 1900s had a much larger grain than movie film from the 50's -- say nothing of the gain in state-of-the-art of movie film and processing used today.
What is the resolution of YOUR movie film? Who knows?! The only thing you need to know, it that the gain in your 8mm or Super 8 or 16mm movie film is 'higher" than the resolution of your TV set. Why? Because NTSC TV standards -- 240 line of horizontal resolution in a TV picture -- were established over 50 years ago -- before digital technology, as we know it today, even existed. Movie film, on the other hand, was developed to be displayed on screens that range from 4x5 feet up to the largest screens found in movie theaters of the era.
