I think this was common with VHS.psycopathicteen wrote:I find it pretty funny how a lot of Europeans online say that skin colors on NTSC appear as either green or purple, yet, I never seen it happen on any of the TVs I had.
What's the reason for the missing PPU cycle on even frames?
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Re: What's the reason for the missing PPU cycle on even fram
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Re: What's the reason for the missing PPU cycle on even fram
It might've happened with rabbit-ear antennas. Those always had lousy reception.
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Re: What's the reason for the missing PPU cycle on even fram
NTSC does have far worse color fidelity than PAL because...
Then again, if I look at some YouTube videos...
- ... multipath reception in antennas and signal reflections in impedance-unmatched electrical connections will cause differential (brightness-dependent) phase shift. Differential phase errors cannot be removed by the viewer using the Hue control, as that one will only correct linear phase errors. The beloved NES being a serious offender. The PAL patent on the other hand explicitly mentions its ability to even remove differential phase errors, as my comparison of the PAL NES' output with Simple PAL versus Full PAL demonstrates.
- ... the very presence of a Hue knob not only in monitors but also in video production equipment meaning one more setting than can and will be improperly adjusted.
- ... a black level of 7.5 percent that was almost impossible to get right without an oscilloscope in the pre-digital days. Basically everyone else, including all PAL countries, use a black level of zero.
- ... RGB primaries that were obsolete almost immediately after the standard was adopted yet never formally changed, leading to confusion among everyone about what the correct colorimetry is, and strange correction matrices in production and consumer equipment. For PAL, the European Broadcasting Union simply said in 1970: here are new primaries based on current technology, and here are permissible deviations: use them and shut up. Worked so well that they were used with minimal changes in HDTV (as Rec. 709).
- ... generally much more lax broadcast and somewhat more lax equipment production standards in NTSC regions (although that's not the fault of the system itself)
Then again, if I look at some YouTube videos...
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Re: What's the reason for the missing PPU cycle on even fram
I wonder how many people would notice if the colorimetry was different without the correction matrices. If you can get a wider color gamut, you might as well show it off.... RGB primaries that were obsolete almost immediately after the standard was adopted yet never formally changed, leading to confusion among everyone about what the correct colorimetry is, and strange correction matrices in production and consumer equipment.
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Re: What's the reason for the missing PPU cycle on even fram
What makes it worse is that NTSC 4.48 is valid for a direct signal and hence the NES and SNES could have given you NTSC 4.48 out of the back which would solve a lot of the problems XD Still won't get you a proper red that doesn't bleed everywhere but you can't have everything
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Re: What's the reason for the missing PPU cycle on even fram
Would ntsc 4.48 work with every ntsc tv set?
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Re: What's the reason for the missing PPU cycle on even fram
Don't know. I mean it in the Spec, and they are analogue devices, so if you change the chroma burst signal faster it should "just work", as in its not digital and hence has a yes/no response to everything. I would think at worst if the internal switching can only handle 3.38 you would still get the same you got now, just the NES outputs more data. Might end up looking worse though.
Re: What's the reason for the missing PPU cycle on even fram
As I understand it, NTSC-only SDTVs are sensitive only to 3.58 MHz chroma.
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Re: What's the reason for the missing PPU cycle on even fram
Is the first one have a ".6mhz" filter on both the encoder and decoder side? Also, the last one DOES look familiar, like it's how my old tv looked like.NewRisingSun wrote:RF video, overall 4.2 MHz bandwidth, equiband YUV decoding at 0.6 MHz.RF video, overall 4.2 MHz bandwidth, equiband YUV decoding at 1.5 MHz. RF video, overall 4.2 MHz bandwidth, 1953 NTSC YIQ decoding with I at 1.5 MHz and Q at 0.6 MHz. This one looks really weird in the yellow-green bushes, because the unequal bandwidths result in funky transitory colors that don't appear with equal bandwidths, even when they're low. Baseband composite video, unrestricted overall bandwidth, equiband YUV decoding at 1.5 MHz: Baseband composite video, unrestricted overall bandwidth, equiband YUV decoding at 3.5 MHz: The last one is never used, because as you can see, the high chroma bandwidth basically steals all the luma detail, and so is pointless.
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Re: What's the reason for the missing PPU cycle on even fram
Does anybody know the formula to convert the original NTSC primaries to sRGB? I remember someone showing a screenshot of the difference between the 2 standards, with the old format having boosted reds.
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Re: What's the reason for the missing PPU cycle on even fram
The formula depends on whether you just want to convert RGB primaries or also from the original Illuminant "C" white point to D65. Use the attached Excel file to calculate from any color space to any other color space. Remarks:
- "Linear light signals" are the signals you get when you remove gamma-pre-correction, i.e. LinearR = R^2.2, 0.0 <= R <= 1.0.
- "Gamma pre-corrected signals" are the normal RGB values you use. As the article referenced in the file explains, proper conversion requires linear light signals. When you use normal gamma pre-corrected signals, you must specify two chromaticity points for which the inevitably resulting errors will be minimized.
- The "Parker (original)" and "Parker (modified)" sheets differ in how white point differences are treated.
- The "Common settings" sheet contains a number of color spaces that the literature lists as being "common" for television sets of a particular era, as well as the color spaces defined by the various standards documents. "sRGB" uses "CCIR Rec. 709" primaries and white point D65.
- The "Gain/Angle" are the result of folding the NTSC YUV-to-RGB* and "Correction for gamma pre-corrected signals" matrices into one matrix and are the values you would enter for example into Nestopia's NTSC palette generator under "Advanced" (Nestopia for some reason requires Gain to be entered divided by two).
- Attachments
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- NTSCPrimaries.7z
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Re: What's the reason for the missing PPU cycle on even fram
Is this what I'm looking for?
Code: Select all
Correction for gamma pre-corrected signals
R's G's B's V U Gain Angle
R't= 1.2903 -0.2705 -0.0198 R'-Y'= 1.628 0.066 1.629 87.7 °
G't= -0.0037 0.9516 0.0521 G'-Y'= -0.557 -0.269 0.618 244.2 °
B't= 0.0317 -0.1982 1.1665 B'-Y'= 0.151 2.445 2.450 3.5 °
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Re: What's the reason for the missing PPU cycle on even fram
No, you are converting approximately and not exactly. To convert exactly, convert to linear light signals and use the formula for linear signals:Notice the gamma conversion formula from SMPTE-170M in the first and last three lines. It is more involved than a standard power function.
Code: Select all
// Convert from 1953 NTSC (with D65 white point) to sRGB color space
float R = (r>=0.0812)? pow((r+0.099)/1.099, 1.0/0.45): r/4.500;
float G = (g>=0.0812)? pow((g+0.099)/1.099, 1.0/0.45): g/4.500;
float B = (b>=0.0812)? pow((b+0.099)/1.099, 1.0/0.45): b/4.500;
float newR = 1.4607*R -0.3845*G -0.0761*B;
float newG =-0.0266*R +0.9654*G +0.0612*G;
float newB =-0.0264*R -0.0414*G +1.0678*B;
if (newR<0.0) newR=0.0; if (newR>1.0) newR=1.0;
if (newG<0.0) newG=0.0; if (newG>1.0) newG=1.0;
if (newB<0.0) newB=0.0; if (newB>1.0) newB=1.0;
r = (newR>=0.018)? 1.099*pow(newR, 0.45)-0.099: 4.5*newR;
g = (newG>=0.018)? 1.099*pow(newG, 0.45)-0.099: 4.5*newG;
b = (newB>=0.018)? 1.099*pow(newB, 0.45)-0.099: 4.5*newB;
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Re: What's the reason for the missing PPU cycle on even fram
I was thinking today about what would be the easiest digital bandpass filter for a system like the NES to do, and I thought that {-1/4, 0, 1/2, 0, -1/4} BPF sampled at 14.32Mhz would be one of the easiest digital filters, so I calculated what would be the -3dB "cutoff" frequency with my calculator and I got:
1.3031574 Mhz
This CAN'T be a coincidence that such a simple digital filter would hit the 1.3 Mhz bandwidth so closely.
1.3031574 Mhz
This CAN'T be a coincidence that such a simple digital filter would hit the 1.3 Mhz bandwidth so closely.