IRE's and middle grey

S

skippyfetus

Carbonite Member
I keep hearing 55 IRE referred to as middle grey when people are talking about digital video. From what I know there's only two ways that 55 IRE could be middle grey.

a) The lowest black level (I forget the term is it 'setup'?) is 0 and the maximum white is 110 IRE, but in digital nothing is recorded over 100 IRE, look at your waveform in Vegas.

b) The starting point is 7.5 and the maximum is 110... that would give you about 55 IRE. I think this is what most people are referring to when they say that middle grey is 55 IRE. However, I thought that digital cameras have started using 0 IRE as the pure black level and it's selectable on cameras like the DVX. So, if cameras are using 0 IRE as the lowest black level and 100 as white that gives you a perfect scale with IRE being proportionate to the percentage of brightness and 50 IRE would be middle grey.

Please enlighten me if I'm wrong.
 
Re: IRE's and middle grey

Blanking level in a video signal is at 0 IRE, ref white at 100 IRE. 55 IRE is about at the middle value of a (0,100)video signal when 7.5% setup is applied (50 IRE if not). Values above 100 IRE involve signal levels allowed for broadcasting (analog modulation). FYI: 50 (55) IRE represents about 18% scene gray in standard 0.5 gamma mode.
 
Re: IRE's and middle grey

That's what I thought... now I forget, what's the default on the DVX 0 IRE or 7.5 IRE setup?
 
Re: IRE's and middle grey

If you let your white levels go to 110, you will invariably get a buzz in the audio. A classic case of this is in the horrible local commercials you see at 3AM. When a overcooked graphic comes on the screen you will here it in the audio.
 
Re: IRE's and middle grey

Still, analog program copies consistantly come from vendors with ire's from 110 to 130. This is a pain in the arse because it's all got to be corrected before distribution and broadcast.

I worked on several international channels of a major cable network and roughly 80-90% of all vendor programming we received failed broadcast standards. One of the most major children's programming production studios never once passed a standards test in over 300 individual programs I tested.

I also don't understand why every major editing software defaults to white levels at 255...that's way above broadcast standards and it bleeds on almost every television in creation.
 
Re: IRE's and middle grey

It's good though for keeping the maximum amount of information on the edited source I guess.

I always cut the whole project, and keep a master, with blacks at 0 and whites at 255, and then make a separate master for DVDs and such going from 16-235. The prospect of a film-out is one that everyone secretly has, even if they don't admit it - and so keeping the extra contrast detail is can't hurt.

just my two cents :D
 
Re: IRE's and middle grey

Oh sorry...I was meaning specifically in the title defaults! White text at 255 is waaaay to hot.
 
Re: IRE's and middle grey

Superwhites (level 255) are not a big problem w.r.t. audio buzz, as long as the signal has not to be broadcasted through analog RF (NTSC).
 
Re: IRE's and middle grey

Superwhites may not buzz, but they look horrid on most consumer televisions, especially at manufacturer's preset contrast/brightness settings. They flare in the overscan and halo everywhere else.
 
Re: IRE's and middle grey

Depends on what the settings are...but superwhites do introduce buzz in all TV receivers based on NTSC RF modulation transmitted signals. A 12.5% minimum restcarrier is the standard for NTSC moddulation. Deeper modulation generated by superwhites inevitably generates intercarrier buzz. Only non intercarrier demodulation based receivers or set applying (ideal) synchronious IF demodulation can cope with deeper than standard modulation
 
Re: IRE's and middle grey

Ouch...don't write stuff like that here, you'll only make me dumber.

I'm really more concerned with the blasting halo that surrounds any superwhite text on anything close to a black background.  As most titleing utilities in most editing platforms default to 0 black and 255/255/255 white...your titles look horrid if you don't make the effort to go in and adjust them.

I just think it'd make more sense to set 250 as the default opening standard for whites and allow the user to select 255 if they so desire.

However, once again, the world does not bend to my will.

Keep your brain handy Andre, we need some science around here every once in a while.
 
Re: IRE's and middle grey

OK I just tried to clarify pennred's remarks on the buzz. B.t.w. many of the today's "digital" CRT TV's just clip the oversized video when digitizeng/remapping and don't show the defocussed white blownups on the screen anymore. So do all flatscreens (LCD,Plasma,..) and non CRT projectors...but the audio buzz remains.
 
Re: IRE's and middle grey

235 would be the more appropriate level, since anything above 235 is classified as "superwhite"...
 
Re: IRE's and middle grey

Yeah, I don't know how I got that typo in there. I set my whites on black to 210 not 250. On FCP I would set them to around 70 out of 100.
 
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