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Behind The Scenes
Color
Resolution -- A Dirty Little Secret
While we see and hear advertised claims of greater and greater TV resolution, published horizontal resolution applies to black, gray, and white only.
Color horizontal resolution is much less, as little as forty lines in many instances. Technical information about this can be found in textbooks available in most public libraries but almost nothing is said about this in advertising.
It is common for TV sets, VCR's, and other video equipment to have even less color resolution than the standards provide for.
Fortunately, digital video and component video connections today allow for much improved color resolution.
Opening Comments
When buying an upscale TV set for home theater, you should try to find and select one with good color resolution for S-video. Unfortunately this is not easy. Differences in color resolution are difficult to see.
Horizontal color resolution of the TV internal circuits is almost never published and even the manufacturer's technical support staff is usually unable to answer inquiries.
In all forms of video, color resolution is deliberately cut so that the color signal will fit in the channel bandwidth or on the disk or tape without interfering excessively with the luminance signal (the latter forms the picture in black and white). Within these limits the NTSC composite video signal is optimized for the human eye's sensitivity to certain colors. Custom and habit, and manufacturing cost cutting, often result in even less color resolution in the finished picture than NTSC is capable of delivering.
There is no easy way of knowing what the preserved color resolution of any given program material is, considering that there are numerous places in the production process where color resolution could be lost. Without source material that has color resolution known to be good, it is more difficult to verify the color resolution of a TV set.
Most of the superiority of DVD over other formats is improved color resolution, and it can be seen only with S-video or component video connections.
Some viewers have reported that they don't see much difference between S-video and composite video. Some viewers have reported they can't tell the difference between component video and S-video. The reason is likely to be poor color resolution in at least one place in the signal path, anywhere from the recording of source material on the disk to the color circuits in the TV.
When you view DVD and HDTV programs today (1998) on a non-computer TV screen, most of the improvement is color resolution. Display limitations such as misconvergence and large dot pitch hide much of the improvement afforded by the increased number of scan lines of HDTV.
Vertical color resolution is equal to the vertical luminance resolution for older analog video. Each scan line can be any color independent of any other scan line. Interestingly, for DVD and most U.S. HDTV and DTV, vertical color resolution is half the luminance resolution; every two scan lines share the same color.
Published Resolution
Here are the published color resolutions for different video formats.
NTSC Composite video -- Format 1 (official): 120 lines theoretical, 100 lines excellent for orange and blue, 50 lines theoretical, 40 lines excellent for other colors, Format 2 (defacto): 50 lines theoretical, 40 lines excellent for all colors. Format 3: 120 lines theoretical, 100 lines excellent.PAL Composite video -- Approximately 120 lines.
S-Video connections -- 140 lines best; specification calls for 120 lines; 105 lines is very good. I am not sure whether 140 lines is actually used for DVD players.
Component video connections -- No real limit, other than that imposed by the specific source material, electronics and cables. Y-Pb-Pr (analog) component video became a standard in order to, in practice, reduce bandwidth requirements over RGB by supplying a higher resolution luminance signal and lower resolution color signals but with more color resolution than S-video.
RGB connections -- No real limit, other than that imposied by the specific source material, electronics, and cables.
Examples
Figures are for NTSC and a 4:3 screen aspect ratio unless noted. We can speak of resolution equally well in terms of lines or megahertz; we have chosen to use lines. For the more technically minded, each additional megahertz of sideband width adds another 80 (79.5) lines of resolution per (distance equal to the) picture height.
NTSC Broadcasts (composite) – 120 lines best, 40 - 105 lines typical for reddish orange to greenish blue; 48 lines best, 40 lines typical for most other color transitions..VHS, S-VHS, 8mm, Hi-8, all Beta (composite or S-video) – The standard is 400 KHz bandwidth yielding 32 lines best, 25 lines typical
12" Laser Disk (composite) – 120 lines best, but could be as low as 40 lines.
DVD (component video) -- 270 lines best, 240 lines typical. Resolution is half of the luminance resolution.
VGA computer monitor -- 480* lines
HDTV (1080i) -- 720* lines (360* lines for some program material). Resolution is one half or one fourth of the luminance resolution depending on production method.. (For a 16:9 picture the resolution is 540 or 270 lines respectively.)
* For computer generated program material. The pixel footprint of all digital video may or may not reproduce closely spaced details as small as one pixel from live subject matter. This lesser resolution achieved is expressed as multiplying the pixel count by a Kell factor .
The NTSC standard has a 1.5 MHz color signal lower sideband width which permits 120 lines of resolution but only for some colors. Earlier (1950's) TV sets probably had circuits that had to start compromising (rolling off) the signal "earlier" starting at say 1.2 MHz (100 lines) to prevent exceeding the bandwidth. Today's circuitry could handle color signals close to 1.5 MHz but then too they might have been dumbed down to handle less.
S-video has a 1.5 MHz standard for 120 lines of color resolution) although we believe the maximum frequency that can be modulated onto the 3.58 MHz subcarrier and then reliably demodulated is half of the subcarrier, 1.78 MHz, allowing about 140 lines of resolution.
Note: "Lines of resolution" in any direction, in this discussion, is correctly measured across the largest circle that fits in the space we are talking about.
The Buyer's Concern
The high end home theater viewer will want to make sure the TV set has good color horizontal resolution after the comb filter. Eighty lines would probably be an absolute minimum; 120 lines is the specification for S-video, but the more the better.
This is not easy. Even knowledgeable salesmen and manufacturers' customer service rep's usually don't know. You might have to call the manufacturer's headquarters. If the resolution is above 80 lines (one megahertz) and the design engineer has some pride in the product, he might give you the answer.
What You Can See
For any TV broadcast viewed up close, you will notice that, going from left to right, any change of color (other than to or from black or white) is blended, smeared if you insist (or has a black gap in between). This is a direct consequence of less than 50 lines of color horizontal resolution for some colors. Colored text is usually deliberately shadowed in black to make this less objectionable.
Provided one of the colors is dark and the other light, fine horizontal detail is not lost completely although the colors actually seen will not be the right colors.
The lesser sensitivity of the human eye to color resolution shortcomings which made NTSC composite video possible also makes judging color resolution more difficult and time consuming.
What to Look For
It is easier to compare two or more TV sets and decide which is "better" or "best" as opposed to looking at just one and trying to decide whether it is "good", "acceptable" or "poor".
The only way you will be able to prove that a TV has good color resolution after the comb filter is to view a program source connected via S-video or component video jacks, such as DVD. In the store, compare one TV against another. Also you can view a nearby TV showing a broadcast to see the consequences of less than 50 lines of horizontal resolution and get a comparative idea of how much crisper color boundaries can be with S-video program material.
The large color bar test pattern reproduced from a DVD such as Video Essentials is a good test to start with. Examine the sides of the seven vertical bars; the smaller the discolored blend area between any of these bars on the top row the better. Notice particularly the boundary between the red and blue and between the green and magenta.
Snell & Wilcox Test Pattern
The only color resolution test pattern I know of is the sets of medium to thin colored vertical stripes near the bottom of the Snell and Wilcox zone plate chart, one of which is recorded on the Video Essentials DVD. There are three tests, for 0.5 MHz or 40 lines of resolution, 1.0 MHz (80 lines), and 1.5 MHz (120 lines).
If you see noticeable dark gaps in the 0.5 MHz (yellow and blue) test, the color resolution is quite poor.
To keep this discussion simple I cannot explain the consequences of sine waves versus square waves here except that an absolutely sharp transition from one color to another requires a square wave while a sine wave represents a blended (or smeared) color transition. Meanwhile the upper limit of resolution or frequency response is where the electronic circuit will reproduce a sine wave but not a square wave of a given frequency.
If there is no red in the 1.5 MHz bars the color resolution is well below 120 lines. If there is no red in the 1.0 MHz bars, the color resolution is well below 80 lines. Be sure to stand far enough back so you do not see the color dots or stripes on a picture tube and also note that poor convergence will greatly confuse the test results.
See, also, web site http://www.snellwilcox.com.
If all the TV sets you are comparing show mediocre color resolution, try a different DVD player or DVD. If you are using source material other than a test pattern, the color resolution might be no better than what a composite signal might deliver.
Some History
The original black and white NTSC picture signal spanned most of the bandwidth for a broadcast TV channel. It so happens that for most real life pictures, the amount of fine detail information is quite small and also occupies a contiguous portion of the bandwidth (towards the higher frequency side).
Color TV records the picture as three video signals for red content, green content, and blue content respectively. Each of these "subsignals" requires as much bandwidth as one black and white signal, and the three all together will not fit in the allotted broadcast channel. It so happens that any three colors, not just red, green, and blue, could be the basis of subsignals used to reconstruct a color picture. With compatibility with black and white TV in mind, the designers chose to transmit luminance, or white/black, with full resolution and two other color pairs (approximately orange/blue and green/purple respectively) at a much reduced horizontal resolution.
Although NTSC broadcast TV provided 330 lines of resolution, most TV sets even back in the 1950's had no more than about 240 lines as a result of manufacturing cost cutting. To define composite video, two color subsignals were modulated onto a subcarrier and then superimposed on the fine detail portion of the luminance signal. On the average (cheaper) black and white TV set, interference was hardly noticed. Those few TV sets (those with full bandwidth and resolution) that experienced problems (a silk screened picture) were often hand modified by a serviceman who added a capacitor amidst the large easily soldered discrete components. That same capacitor, tinier nowadays, is still found in today's TV sets without comb filters.
While the three colors red, green, and blue are needed to make a video picture, for details in the 40 to 120 "lines of resolution" range (medium details) only two primary colors, reddish orange and greenish blue, will suffice. Still smaller picture details can be left uncolored. Viewed by itself such a picture (ultimate NTSC approximates this) looks very natural although of course it looks inferior compared to today's DVD picture.
To make the luminance/color interference tolerable and keep the total signal within the allotted channel space, the color signal bandwidth and therefore the color resolution had to be reduced. Since the human eye is more sensitive to reddish orange and greenish blue, one color component signal (called I for in-phase) is based on these colors. A second component (called Q for quadrature modulation) is based on greens and purples such that combinations of I and Q could produce any color. The I signal giving 120 lines of resolution (wideband relatively speaking) and the Q signal giving 40 lines of resolution (narrow band) gave the best resolution compromise. In order to finalize the NTSC standard, viewers' opinions of picture quality were gathered using laboratory tests involving different combinations of luminance and color content. Reception of the same signal on black and white TV sets was also taken into account as the final NTSC standard had to be compatible.
While the color information was commingled with and overwhelmed the fine detail luminance information, both could be separated using a comb filter.
Comb filters in those days were much too expensive, so no consumer TV sets would give full 330 lines of luminance resolution and 120 lines of color resolution for decades to come. Whether or not that was the design goal back in the 1950's, the NTSC composite signal as defined included a lot of extra picture quality for the TV sets of the future. That future is now (1980's and after).
Dumbing Down
Unfortunately more manufacturing cost cutting and video production cost cutting moved the consumer TV industry away from the optimum NTSC color picture and for the worse. Incidentally, when consumer VCR's and camcorders came on the market they gave about 30 lines of color resolution for all colors and analog ones still do no better today.
In the process of handling the luminance and color, the color signal became delayed requiring a matching delay circuit in the luminance signal path. The different bandwidths of the I and Q signals resulted in different delays for each so additional delay circuits were needed. TV set makers started to cut the I signal back to 0.5 to 0.6 MHz to match the Q signal so only one delay interval would have to be dealt with.
By the mid 1970's the B-Y and R-Y signals we use today in "component video" started to get widespread use in TV color decoders. The I and Q signals, being more complicated and expensive to work with, started to give way to B-Y and R-Y (referred to as U and V respectively when modulated upon a subcarrier for constructing composite video). Neither of the latter is optimized for the red-orange and green-blue medium detail primaries, and at first it was common to provide just 40 to 48 lines of resolution for all colors. In fact, the early usage of U and V was referred to as narrow band color. We believe that there were a few non-standardized instances where the V signal was given a 1.5 MHz bandwidth. One recent reader writes that some laserdisks are made with 1.5 MHz or even 2 MHz bandwidth for both color components. We have not verified this nor heard of problems of common comb filters' being unable to filter this much chrominance information.
Although S-video standards provide 120 lines of resolution, a manufacturer (which we won't name) admitted that the color decoder they used for S-video as well as composite video had only 60 lines of resolution.
Contemporary standards (e.g. SMPTE 170) favored more resolution for all colors, especially for certain satellite broadcasts and recording on DVD's. In order to produce both a wideband color signal for S-video and a truly correct NTSC composite signal, two C signals (I and Q mixtures) would have to be created. For making composite video the Q signal has to be band limited (to 0.6 MHz) prior to being combined with the I signal. For S-video the Q signal must retain a 1.5 MHz bandwidth during the construction of the C signal. The B-Y, R-Y (U and V) color signal pair can be used equally well to construct the C signal as used for every purpose except correct NTSC composite video.
After U is combined with V, or if Q is combined with the I prior to band limiting, to make a C (color) signal, it is not possible to reduce the signal energy in certain critical parts of the frequency band to conform to NTSC composite standards without reducing the reddish orange and greenish blue to 48 lines of resolution as well. Some broadcasters used it anyway, limiting all the colors to 48 lines, probably rationalizing, probably correctly, that most TV sets didn't reproduce more than 48 lines for any color. The laser disk buyer cannot easily tell in advance whether the program material has lost color resolution for this reason during the production process.
This argument, I fear, has reached TV manufacturing, why provide 120 lines of color resolution just to receive broadcasts with only 48 lines and play back tapes with only 40? While only a small percentage of TV sets may have that restricted color resolution, it is up to the buyer to find out and avoid the ones that do.
A few years ago, the more upscale TV sets would have brochures that advertised "high video bandwidth" to emphasize the higher luminance horizontal resolution. Manufacturers never did and still don't say anything about the color resolution. With S-video and component video program sources, consumers will have to be more careful in selecting a TV set that does have better color resolution.
If the TV set has an excellent comb filter that removes most of the dot crawl but has only 48 lines of color resolution in the circuits that follow, picture quality of an S-video feed will be degraded almost to that of a composite feed. A component video feed might then produce a picture almost indistinguishable from an S-video feed. (This difference or lack of difference can also be attributed to misconvergence on the screen.)
We can just hope that an HDTV compatible TV has better color resolution but it is still a good idea to verify that using the viewing tests suggested earlier.
Some TV sets decode the C color signal into I and Q, most decode it into U and V. For run of the mill TV sets and others with just 0.6 MHz chroma bandwidth, video constructed from I and Q and video constructed from U and V will both be decoded equally well regardless of whether the decoding circuits use I and Q or use U and V. Either way, red, green, and blue components are eventually constructed for feeding to the picture tube. Some complications arise when decoding wide band color such as correct NTSC color with the 1.5 MHz lower sideband, although for the most part any errors are hardly noticed by the viewer.
Extended Color Resolution for Laser Disks
For non-aerial transmission of video, the 4.2 MHz upper limit does not apply and luminance information goes up to 5.3 MHz (425 lines) for laser disks and 7.0 MHz (540 lines) for DVD. This permits even composite video to carry 120 lines of color resolution, and either YUV or YIQ encoding could be used. This writer is not sure whether laser disks actually take advantage of this. However if color information did extend above 4.2 MHz, very few TV comb filters reach that high to capture it and for those sets the overall color horizontal resolution would remain 48 lines based on 0.6 MHz.
Component Video and Digital Video
Digital video usually uses the same color components as analog color difference component video: luminance (Y), R-Y, and B-Y. It is still necessary to transmit and store the color components with less resolution due to space and bandwidth limitations. The most common formats for digital video have one color pixel (one R-Y and one B-Y element) for every two by two block of luminance pixels (4:2:0), or one color pixel for every four luminance pixels in a row (4:1:1). Read the number codes (X:Y:Z) as: "for every X luminance pixels across there are Y color pixels on the odd scan lines and Z color pixels on the even scan lines".
For a composite video signal with 330 lines of resolution (per 4:3 picture height) and 40 lines of color resolution, this translates to approximately 440 luminance pixels and 52 color pixels per scan line, for a ratio of 8-1/2 to one. However the color may not be stored as a 480 x 52 pixel matrix, otherwise further degradation will occur. A color detail might span pixel positions 1 to 8 on one scan line and positions 3 to 10 on the next scan line, this cannot be accurately reproduced with the color digested down to a 480 x 52 matrix.
Where Might Excessive Loss Occur?
1. If the camera has separate pickup elements (CCD or comparable) for luminance and color and the one for color has far fewer pixels of resolution,
2. As the color components (either the I and Q pair or the U and V pair) are generated from the camera RGB signals and the bandwidth either by design or improper adjustment is too small,
3. As the color components (either the I and Q pair or the U and V pair) are generated by a DVD player as the disk is played and their bandwidth either by design or improper adjustment is too small
4. (mentioned above) As the C signal is band limited just prior to combining with the luminance signal to become composite video for broadcast or recording on laser disks.
5. During comb filtering; all comb filters split the incoming signal into different frequency bands, which some comb filters might make too narrow,
6. (mentioned above) In the TV set color circuits that follow the comb filter, if they are skimpy enough to barely pass the color from composite video,
7. When recording using any consumer grade VCR; the bandwidth of the recorded color signal is enough for at most 32 lines.
8. If the cables connecting the various devices are too long or of poor quality.
Semitechnical Explanation of I and Q versus U and V
If you remember taking high school geometry, the horizontal X-axis and the vertical Y-axis will come to mind. Or you can think of a road map with letters going down the left side and numbers along the bottom, for example A-1 might be the top left corner and D-5 is somewhere in the middle.
Think of a color wheel, with red on top, then clockwise to magenta, then blue on the right, then turquoise on the bottom then green, then yellow on the left and so on. Let's put black in the center and pastel colors along the borders of the page. With this color wheel, U stands for left to right and the V stands for up and down..
Next think of the same wheel turned a bit so orange is on top, purple is to the right, blue is on the bottom and green is to the left. For this wheel, Q stands for left to right and I stands for up and down. You can still describe any color as somewhere on the I scale and somewhere on the Q scale.
Two color components (I and Q, or U and V) are needed because the color wheel occupies a two dimensional space. If there was just one color component, you would have to think of all the possible colors along one straight line. The electronic complexity of representing all the colors as one component signal versus two is comparable to the mechanical complexity of blending all shades of all colors on a thin strip of paper (it would have to be hundreds of feet long) as opposed to one 8-1/2 by 11 inch page with a color wheel drawn on it.
Lesser color resolution means you will see on the screen more readily the blending of the edges of adjacent colors somewhat analogous to following a straight line from one spot to another on a color wheel.Sometimes a gap of white or black occurs between the adjacent contrasting colors. Lesser color resolution means that as the electron beam draws a scan line, it may be unable to get all the way from one desired color to the next before it has to start changing to a third color for a spot yet further along the scan line.
The terms I, Q, U, and V refer to the color component signals already modulated onto the color subcarrier, approx. 3.58 MHz for NTSC and about 4.43 MHz for PAL and SECAM. Simply adding the C signal to the Y signal produces composite video. The U signal when demodulated becomes the Pb (B-Y) part of component video. The V signal when demodulated becomes the Pr (R-Y) component. PAL and SECAM have always used U and V rather than I and Q. On alternating scan lines the SECAM "C" signal consists of just the U or just the V. NTSC can (and often does) use U and V rather than I and Q to construct composite video, usually at the expense of restricting all colors to 48 lines of resolution.
Some Problems Decoding Wide Band Color
The description below is theory. We are not sure which manufacturers did what. With NTSC composite video being superceded by digital video, this discussion is becoming of lesser importance except for video history.
Modulating the color (chroma; C) signal on the (approx.) 3.58 MHz subcarrier is at first glance comparable to any amplitude modulation with sidebands above and below the carrier being created. For normal amplitude modulation the sidebands are "mirror images"; one sideband could be deleted (filtered away) and the entire signal could be recovered (demodulated) using just the other (known as single sideband transmission and reception) although the electronics needed are more complex. For NTSC color, the two sidebands are not the same. The technical term for this modulation is quadrature modulation which we will not describe in detail here.
Here are some methods of encoding the NTSC C signal, summarized:
A -- Correct NTSC -- Is constructed from a (n approx.) 1.5 MHz I signal and an 0.6 MHz Q signal.B -- Narrow Band Color -- Is constructed either from 0.6 MHz U and V signals or 0.6 MHz I and Q signals, either yielding the same result.
C-- Super Wide Band Color -- Constructed from 1.5 MHz V and U signals or 1.5 MHz I and Q signals, either yielding the same result. Feasible for laser disk and for the composite output of DVD players where the total composite video bandwidth could exceed 4.2 MHz, although probably not always used.
D-- Cropped Super Wide Band Color a.k.a .Super NTSC -- Constructed from 1.5 MHz V and U signals but the upper sideband has been limited to 0.6 MHz for example if a DVD or LD player's output was modulated onto a broadcast channel to feed a TV set with no A/V input.
Here are some methods of recovering the color information:
F-- Correct NTSC -- Color decoder yields a 1.5 MHz I signal and an 0.6 MHz Q signal.G -- Narrow Band Color -- Decoder yields 0.6 MHz U and V signals, or rarely 0.6 MHz I and Q signals.
H-- Super Wide Band -- Decoder yields 1.5 MHz U and V signals which is the full S-video quality.
J --. YVQ -- One mention was made of a specific TV set maker using a color decoder that yielded V and Q rather than U and V. The bandwidth was not specified so we cannot speculate on its performance. Its significance is that any two color pairs, not just the reddish orange and greenish blue of I or the bluish red and cyan of V or the blue and yellow of U can be the color decoder's two color outputs.
Let's compare the results of using these decoders for the different encodings of NTSC color.
Decoder F will recover color correctly from encoding A.Decoder F will recover color correctly to the limit of 0.6 MHz in the source material via encoding B.
Decoder F will recover color correctly for coarse details; color of medium details will be rendered as black and white or red-orange/green-blue regardless of their original color when the encoding method is C or D.
Decoder G will recover color correctly (to the extent of its limited 0.6 MHz bandwidth) from any of the above encodings A, B, C, or D.
Decoder H will recover color correctly for coarse details while the color of medium details is unpredictable when the encoding method is A or D.
Decoder H will recover color correctly to the limit of the 0.6 MHz source material color content of encoding method B; there may be more noise compared with using decoder G.
Decoder H will recover color correctly from encoding C.
Other comments
All of the picture differences pointed out here are extremely subtle, and probably could not be identified unless pictures from two of these methods were shown side by side and the viewer asked which picture was "better".
For true NTSC encoding and for medium horizontal color detail represented by the 0.6 to 1.5 MHz range, only the lower sideband is preserved. Decoded as YIQ in the TV set, the same I circuit that decodes the coarse detail (0 to 0.6 MHz) will recover it properly. Nothing but noise is expected to show up above 0.6 MHz in the Q decoder circuit and the latter is usually low pass filtered to 0.6 MHz anyway to clean up any such noise.
An older but good decoder (F) decoding a super wide band (C) color signal will still give very good results. If only two colors (plus grays) were available for the rendering of medium details, red-orange and green-blue work best.
Most color decoders, both YUV and YIQ, skimped and cut back all color to 0.6 MHz (narrow band; type G above). They would work properly regardless of whether the source was consructed via YUV or YIQ.
We are still unsure of why only the Q signal (greens and purples) in NTSC color was restricted to 0.6 MHz. One reason could be that having both I and Q at 1.5 MHz would put too much color information in the 2.1 to 3.1 MHz part of the luminance signal and result in excessive dot crawl and graininess. Another reason put forth was the inability, at least at reasonable cost, to decode both I and Q when the corresponding upper sideband of the C signal at 4.1 to 5.1 MHz was missing. Yet Faroudja Laboratories (now part of Sage Inc.) was at one time proposing a "Super NTSC" based on the cropped super wideband color (format D) discussed here, where both I and Q were 1.5 MHz.
Wide band color decoders are desirable for applications using S-video. A super wide band color decoder similar to #H but decoding YIQ can be constructed to decode A, B, and C correctly and give an excellent decoding of D. It would have selectable options: (a) 1.5 Mhz I, 0.6 Mhz Q to decode A and D, (b) 0.6 Mhz for both I and Q to decode B, and 1.5 Mhz for both I and Q to decode C. Low pass filters and delay circuits are used to obtain the various options; the color decoding circuitry is the same for all options. Unfortunately, with the advent of digital video, NTSC composite video is gradually becoming of lesser importance and no manufacturer we know of has come forth with such a decoder.
For a wider band YUV color decoder to work properly with correct chroma from an NTSC broadcast, it would have to segregate the 0 to 0.6 MHz output from the 0.6 to 1.5 MHz output the latter of which both the U and V demodulator outputs would possess. The two lower band signals would be used as-is. The two higher band signals are not sufficient to define the proper color since their phase would be ambiguous with different hues at slightly different horizontal positions. Instead the best way to utilize them would be to combine them used to drive both the U and V circuits following in phase producing just reddish orange and greenish blue for the medium color detail. This technique would also work with wideband V and narrow band U incoming signals but rendering the medium details as red-orange and green-blue isntead of red and cyan. Even so, there may still be some horizontal spatial error comparable to a poorly done child's coloring book. Segregating the 0.6 to 1.5 MHz portions, blending them, and sending the result to both the U and V circuits also reduces this spatial error. However when the chroma signal has both sidebands out to 1.5 MHz, as is the case with S-video, the wide band color decoder needs to use the entire U and V outputs as is, without segregating and blending as described here.
We have reason to believe that, due to cost, no wideband color decoders exist that segregated the low color detail from the medium color detail as described above. Rather they simply allowed unpredictable colors to be rendered if the incoming color signal had one but not both sidebands for the medium color information.
The problems of cropped super wide band color (D) are rarely seen since that condition rarely occurs except when baseband video is modulated onto an NTSC broadcast channel, and then band limited to 4.2 Mhz. Furthermore these problems are subtle to begin with and are generally masked by the imperfections of typical TV tuning circuits or imperfections of the RF modulator in LD players or purchased to go with a DVD player.
Some experts have questioned the legality of NTSC broadcasts lacking medium detail color information such as from source material recorded on consumer grade VCR's including S-VHS and Hi-8. This would be no less legal than broadcasts transmitted over coaxial cables back in the 1950's, the bandwidth was about 3 MHz and the finer luminance details (and all ability to recover color information if it was a color broadcast) were lost.
Viewed alone, pictures with incorrect medium color detail
rendering would not stand out as being incorrect due to the already limited
human visual acuity of color detail. But they would look inferior in a side by
side comparison with correctly constructed (YIQ) and correctly demodulated
broadcast presented on a high quality TV set.
