Yes, I'm talking about this.NewRisingSun wrote:I think he's asking about out-of-range R/G/B levels coming out of the color decoder after all automatic gain controls have been applied, which happens quite often in the NES since it does not start with R/G/B to begin with.
How about not so old? in 1995 there was already tvs that had OSD for example.NewRisingSun wrote:I cannot imagine any analog TV adding DC to the entire RGB tuple just because one of them goes negative, and all old TVs that I have seen certainly didn't.
Also, perhaps some circuits may clamp somewhere in matrixing, or I don't know.
Anyway. Here is what it looks like now:
Almost all colors has some clipping issue.
Yes, I was trying to reduce contrast until all clipping values will fit. In result I had 0.5 contrast (half).
I thought it has only mario inside. I would like to check normal PAL TV recording.NewRisingSun wrote:There is one partial PAL raw recording in this post. Partial because the capturing program is for NTSC only, and so still samples only for 1/60th time at 8*NTSC-Fsc.
Regarding AGC. I wan't to know how I should exaclty scale voltages into IRE.
I don't think that decoder is forecaster of what white level is, without having white on screen.
So, it has to align voltages according to some rules without information about colors on picture.
At this moment I simply set color 1d to black = 0 IRE and white color 30 to 100 IRE.
Perhaps I should do this in other way. For example white is 120 IRE.
One additional note.
Consider decoded is R'G'B'.
Its theoretical luma is: 0.299R'+0.587G'+0.114B'
Now, assume R' is negative.
Then, clipped luma is 0.587G+0.114B, and it's greater than theoretical, because R is negative.
That's why I even started to think about this issue.
Similar consideration leads to darker clipped luma for colors which have component over 1.
I still don't get it though. Why we use linear transforms and equations for colors which are gamma precorrected.
As far as I understand, they have 1/2.2 gamma, and so you have to correct them to linear first.
Also, I was trying to assume that R'G'B' have 1/2.2 gamma, and then correct to RGB, and assuming that it is CIE RGB,
convert to XYZ, and then convert to sRGB. I got some trash in the end.