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Why do people object to the term "4K"?
Red routinely refer to the RED One as having â4Kâ horizontal resolution. Many people object to this claim; what are their reasons for doing so?
Note: This not intended to be a discussion of the relative merits of the RED One or any other camera. It is merely an attempt to clarify what it is people tend to object to, without getting involved in pointless arguments about which system is better. Remember: this describes the mindset you are up against, not so much the problem itself.
The main objection is simply the fact that in film scanner terminology that long preceded the RED One, â4Kâ specifically meant that each of the 4096 individual pixels in each horizontal row are individually âinterrogatedâ by separate red, green and blue sensors. That is, the data from a single row of pixels consists of 4096 trios of red, green and blue pixels, a total of 12,288.
Stating that the RED One has â4Kâ horizontal resolution implies that the decoded colour images produced by the RED Oneâs Mysterium sensor are similarly made up of 4,096 trios of RGB pixels. That would indeed be the case if the camera used three 4K sensors and a dichroic beam splitter prism as is used in â3-Chipâ cameras. In reality, the use of Bayer masking means that in each of the 4,096 rows of photosites on the underlying monochrome sensor, each photosite only responds to a single colour; red, green or blue. That is, two of the colour values of each pixel are not measured and have to be estimated from the values in the surrounding pixels
So while the final â4Kâ output may well consist of 4,096 RGB values per horizontal row of pixels, these values are the result of calculations and guesswork by the processing computer, not actual measurements. Some people outright regard this as misleading, but most people are simply concerned by the difficulty of pinning down the actual resolution. Manufacturers often show images taken of test charts, but in the past at least, cameras and other types of video apparatus have been notorious for giving far better results shooting test charts than they do shooting real images!
This contrasts with 3-chip designs (or single-chip cameras with straightforward RGB filter arrays such as the Panavision Genesis): In those the output is perceived as very much âwhat-you-see-is-what is-actually-thereâ and even relatively non-technical users can feel comfortable that they understand their principle of operation. (Whether they actually do is beside the point, if they are the ones writing the checks!)
While Bayer Masking can produce perfectly acceptable results, and is in fact the principle used by the bulk of digital still cameras, people still tend to question the validity of a system that depends on an automated processor to make âbest guessesâ about data that is not actually captured. Itâs one thing to get a couple of substandard shots in your stills camera, itâs quite another to have to âPlease Explainâ on a multi-million dollar commercial or ad campaign.
Whether any of the above are valid concerns or not will not be passed upon here. The reality is that in its currently used form, the RED One does not seem offer enough clear advantages to offset the risk of endorsing a system that for many Industry people, remains very much an unknown quantity.
Creative Pixel Accountancy (CPA)
It is important to understand the difference between the source resolution and the number of display pixels.
Before the days of digital signal processing, determining the output resolution of a video source was a pretty straightforward affair. Whatever number of scanning lines, frames per second etc the camera or other video source produced, every TV set or monitor displaying the images had to reproduce exactly those numbers on the screen. In a television broadcast to a large city (or even the whole country) all the millions of TV receivers had to be precisely synchronized to the master oscillators in the TV station. Similarly, every piece of video equipment used to output the program had to be âGenlockedâ to the master station sync.
With the development of standards converters, timebase correctors and frame stores in the 1970s it at last became possible to remove the stranglehold of genlocking, meaning that non-synchronized video sources could then be freely intermixed with genlocked studio sources.
This also meant that overseas-sourced video on different TV standards could be fed into the studio data stream, which introduced the concept of re-mapping pixels. For example 625 line 25 frames per second PAL into 525 line 29.97 frames per second NTSC.
With the recent proliferation of low-data-rate video sources, technology became available that could also convert extremely low-resolution images (from Webcams, cellphones and the like), to 625 or 525 line PAL or NTSC. By no means does that mean that the output signals have anything like the possible resolution of PAL or NTSC, all this was ever intended to do was allow the low-resolution, low-frame-rate images to be viewed on conventional TV sets.
Probably the most common application of this is/was allowing digital still cameras to capture basic but useable video on flash memory and display or record it on standard TV equipment. Typically the captured images would be around 320 x 240 pixels in size with a capture frame rate of around 10 fps. The cameraâs internal processor would re-map the image data onto PAL or NTSC video that could be displayed on a standard TV set.
While that practice is perfectly legitimate, there is an increasing tendency for manufacturers to apply similar processing to signals that are only ever stored as file data. So we have a rash of pocket âspycamâ gadgets which can only produce a measured resolution of, for example, 200 x 150 pixels and 15 frames per second, but they are advertised as âVGA 640 x 480 30 fpsâ .
Since most of these gadgets have no direct video output capability, there is no meaningful justification for this âuprezzingâ of the original data, since the files can only ever be displayed on computers that are perfectly capable of doing this themselves. In any case, even actual 640 x 480 VGA normally gets displayed on whatever number of pixels the user chooses.
âVGA 640 x 480â is basically broadcast standard NTSC, and with the right source material, is capable of extremely good picture quality, as witnessed by NTSC component video from a DVD player. The only thing this has in common with video from a cheap camera is that on a CRT-based TV monitor, the line and frame rates are the same. Otherwise, the effect is approximately equivalent to using the very best NTSC camera available, to shoot VHS playback off a TV screen.
A simple illustration of CPA is to use Microsoft Wordâs âInsert > pictureâ function to insert an image into a blank page. The file can be saved under the name (for example ) âsmallpicture.docâ. Then, right-clicking on the image and using one of its âsizing handlesâ allows it to be stretched to a larger size (say with four times as many pixels). The Word file is then saved under under a different name eg largepicture.doc. Checking âPropertiesâ for each file, it will be noted than they have exactly the same size file! So even though the imbedded image appears to have four times as many pixels, no more actual data has been generated.
Unfortunately, CPA is not confined to pocket spycams and the like. The majority of so-called â1080pâ video cameras do not actually produce 1920 x 1080 images. What they do produce is a considerably lower resolution image which is then re-mapped onto 1080 x 1920 pixels.
This might have had some justification a decade ago, when virtually all monitors capable of displaying a 1080 x 1920 raster were CRT-based, but the notion of having to format everything to suit a one-size-fits-all video format is basically a World War II-era concept; most monitors and editing systems these days can handle virtually anything that is fed to them.
âIf that was true thenâĤâ
Note: Again, this is an awkward question you might be called upon to answer, not an invitation to a debate!
A point that is often raised is that if it was really possible to produce a true â4Kâ output from a 4K monochrome sensor with a Bayer Mask, it should also be possible to produce true HD (1920 x 1080) RGB output by Bayer Masking a single 1920 x 1080 monochrome sensor, of the type that have been used in 3-chip HDTV cameras for the past 15 years. While cameras with such sensors are available, they do not produce anything like the image quality of a camera that uses 3 such chips and a dichroic prism for RGB separation.
At present there are no 4K versions of the popular 2/3inch 1920 x 1080 3-chip format, although the technology to achieve it is certainly available. The main reason no such products exist is simply that there is currently no perceived market for them. However this could well change with the development of affordable â4Kâ projection and other display technologies.
One would also have to ask what such a device would be called, since â4Kâ appears to be already taken.
