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iPhone 4's "Retina Display" Claims Challenged
adeelarshad82 writes "Of the many things that buyers might need to know about the new iPhone, Raymond Soneira — president of DisplayMate Technolgies — added one more to the list. Soneira challenged Apple's claims that Apple's new iPhone contains a so-called 'retina display.' According to Soneira, the resolution of the retina is in angular measure, 50 cycles per degree, where a cycle is a line pair, which is two pixels, so the angular resolution of the eye is 0.6 arc minutes per pixel. So, if you hold an iPhone at the typical 12 inches from your eyes, that works out to 477 pixels per inch. At 8 inches it's 716 ppi. You have to hold iPhone 4 out about 18 inches before it falls to 318 ppi. So the iPhone has significantly lower resolution than the retina."
Also remember, the colour resolution of the eye is far poorer than the b&w resolution of the eye, and the aim here is about colour.
I'm not entirely sure what you mean, but the fovea responsible for your "high resolution" sight contains almost exclusively cones, which are colour sensitive. Most of them detect red and green light, so the resolution in monochromatic red or green isn't that far below white light.
The rod cells on the other hand can only distinguish between black and white, but they are much sparser giving significantly lower resolution. (Their advantage is that they are extremely light sensitive, almost down to detecting a single photon. This is why you have no colour vision when it is dark. Another interesting consequence is that you are blind in the center of your visual field when light conditions are bad, since the fovea lacks rods.)
What does that translate to in terms of halftone printing? There's a world of difference between 90000 dye-sublimation continuous tones per square inch, and 90000 little squares that can be exactly black, cyan, magenta, or yellow. That's one reason why a "300dpi" magazine like Playboy still looks richer and better than the 1200dpi output of a color laser printer, and why an inkjet printer almost always produces better-looking continuous-tone images (ie, photos) than any laser printer. A 1200dpi color laser printer uses most of its resolution to get better interpolation. An inkjet printer that sprays magenta ink over yellow ink produces a muddy orange as long as the yellow ink is still wet. A laser printer that prints magenta over yellow will end up with... magenta. Likewise, a true laser printer can (in theory, at least) do more with 300dpi than a "LED" laser-like printer, because the laser's brightness and beam diameter can be modulated a bit, so you can simulate real halftone patterns a bit more easily. In contrast, a LED laser-like printer is going to charge rectangular areas of constant dimension, so your resolution is literally *it*.
It's kind of like trying to argue about the true resolution of a recent-vintage DLP light engine. In the old days, a DLP TV with 1280x720 resolution literally had 1280 x 720 little micromirrors on the DMD (well, more for overscan purposes, but it was basically a 1:1 correlation between a single micromirror and a single rendered pixel on the screen). Then, someone (Samsung?) figured out that if you used a brighter light and modulated their movement at a higher rate, you could use one mirror to illuminate a pair of adjacent pixels. Then the whole definition of native DLP resolution kind of went to hell, because nobody knew what a pixel of resolution on a DLP TV meant anymore.
If you really want to get depressed, try shopping for a HD video camera that's more than a hundred bucks, but less than $10k. There's a huge gray area in between, and the liberties that some manufacturers (not necessarily the lowest-end Chinese imports, either) take with their advertised resolutions is borderline fraudulent. There are cameras with interlaced sensor modules that claim to be progressive by virtue of double-buffering a pair of fields internally and outputting them sequentially. There are cameras that alternate the sensors red-green-blue-green-red-green-..., then count a red-green pair as one pixel, and the adjacent blue-green pair as another pixel (hey! instant resolution-doubling makes the marketing department happy). It's sad, but in 2010 we're still reduced to taking digital photographs of black and white angled lines and using the same metric people had to use a hundred years ago for lack of a better way to describe camera resolution. 10 years ago, if you bought a camera with 1280x960 resolution, you knew damn straight it had 1280 clusters of red, blue, and green sensors horizontally, and 960 of 'em vertically. New cameras, alleged to have near-gigapixel resolution, commit frauds that basically amount to counting the number of discrete sensors sensitive to any wavelength of light, then play games with interpolation algorithms to see just how high they can claim their resolution is without getting indicted by state attorneys' offices for false advertising.
Not to be pedantic, but CD audio quality is 44.1 kHz
44.1 kHz is the sampling frequency, 20 kHz is the audio signal frequency. According to the Nyquist-Shannon Sampling Theorm in order to accurately capture a signal you need to sample at least at twice the rate of the highest frequency you want to capture. That means you should sample at a minimum of 40 kHz to accurately capture 20 kHz signals.
Now, you want to overshoot a bit because of how the filters work so you should choose a sampling rate that's a bit higher than the minimum necessary. They chose 44.1 kHz partially for this reason, but also because of the reason found on this site:
From John Watkinson, The Art of Digital Audio, 2nd edition, pg. 104:
In the early days of digital audio research, the necessary bandwidth of about 1 Mbps per audio channel was difficult to store. Disk drives had the bandwidth but not the capacity for long recording time, so attention turned to video recorders. These were adapted to store audio samples by creating a pseudo-video waveform which would convey binary as black and white levels. The sampling rate of such a system is constrained to relate simply to the field rate and field structure of the television standard used, so that an integer number of samples can be stored on each usable TV line in the field. Such a recording can be made on a monochrome recorder, and these recording are made in two standards, 525 lines at 60 Hz and 625 lines at 50 Hz. Thus it is possible to find a frequency which is a common multiple of the two and is also suitable for use as a sampling rate.
The allowable sampling rates in a pseudo-video system can be deduced by multiplying the field rate by the number of active lines in a field (blanking lines cannot be used) and again by the number of samples in a line. By careful choice of parameters it is possible to use either 525/60 or 625/50 video with a sampling rate of 44.1KHz.
In 60 Hz video, there are 35 blanked lines, leaving 490 lines per frame or 245 lines per field, so the sampling rate is given by :
60 X 245 X 3 = 44.1 KHz
In 50 Hz video, there are 37 lines of blanking, leaving 588 active lines per frame, or 294 per field, so the same sampling rate is given by
50 X 294 X3 = 44.1 Khz.
Sapere aude!
What does that translate to in terms of halftone printing? There's a world of difference between 90000 dye-sublimation continuous tones per square inch, and 90000 little squares that can be exactly black, cyan, magenta, or yellow. That's one reason why a "300dpi" magazine like Playboy still looks richer and better than the 1200dpi output of a color laser printer...
If you're actually interested:
"300dpi" is something of an oversimplification. Images are sent down at 300dpi. The printing plates are usually imaged by laser at 2400dpi, but each halftone cell takes up more then one "dot". Print resolution is measured in "lines per inch", and ranges from ~85 lpi for newsprint to over 200 lpi for higher end printing. I'd guess that playboy prints much closer to the 200lpi end of the spectrum.
A "1200" dpi inkjet (usually more like 1440dpi) will be able to print 1440 dots per inch, but multiple dots are needed to make each halftone cell. In effect, even the best consumer level inkjets are half the resolution of an offset press.
As for laser printers, if you look at the industrial level digital presses (many of which are really glorified laser printers), they produce print that is much closer to the level of an offset press, but then again they can cost well into the six figures, so I guess you get what you pay for.
Apple has never claimed not to be evil, they're just very stylish about it.