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 Post subject: Contrast and Brighness
PostPosted: Sep Mon 07, 2020 11:31 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2098
Location: Waukegan, IL
Is there a method to setting contrast and brightness? I heard somewhere the brightness control was really to set the black level and the contrast control took care of the white.

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 Post subject: Re: Contrast and Brighness
PostPosted: Sep Tue 08, 2020 12:31 am 
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Joined: Apr Sat 06, 2013 2:18 pm
Posts: 570
Location: New Hampshire
Oh boy a bomb tosser !
IMHO brightness sets the brite to a comfortable level for the room light.
Contrast can be to low & give a washed out pix. If to high too much difference
between blacks & whites eliminating the greys.
Keep in mind olds sets especially colors look MUCH better in a dark room.
Focus, resolution detail in bright areas are better. As a bonus you get a cooler
running set.
Some sets in the 70's combined brite & contrast in one control sometimes with
a light sensor & color level also. I always turned all that crap off & manually set it to my
liking. Just left the AFT on.

73 Zeno 8)
LFOD !


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 Post subject: Re: Contrast and Brighness
PostPosted: Sep Tue 08, 2020 1:52 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 1149
Location: Belrose, NSW, Australia
IF the TV has DC coupled video and
ASSUMING the beam current is not triggering the beam current limiter, then
YES, Brightness is Black Level and Contrast is White Level.

This does not apply to most US vintage TVs, that commonly have AC coupled video. Of these sets, the brightness / black level is determined by the average picture level.
This means that the appearance on the screen of a bright object will force the black level to "blacker than black". In the process you can lose the darker parts of the picture..

Arguments used to rage about which was the better method, AC or DC coupled video. With vacuum tube equipment it was more difficult to maintain accurate black level, both at the transmitting and receiving ends. AC video made things easier.

With color, it's highly desirable to have DC coupled video for correct color rendition.

When I'm restoring an old TV for my own use that has AC video I will usually modify it for DC video. Floating black levels spoil my enjoyment of the program.

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Last edited by irob2345 on Sep Tue 08, 2020 4:07 am, edited 1 time in total.

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 Post subject: Re: Contrast and Brighness
PostPosted: Sep Tue 08, 2020 2:09 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2212
Location: Lafayette, CO
I work on late '40's sets....l adjust to where the retrace lines just show up. High voltage being in spec is good, too. Craig


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 Post subject: Re: Contrast and Brighness
PostPosted: Sep Tue 08, 2020 4:12 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 1149
Location: Belrose, NSW, Australia
Yes, early on, it was common to restore the black level. This fell by the wayside as the average punter couldn't tell the difference.

With DC restoration, blanking the retrace (which is "blacker than black") could be regarded as optional if controls were correctly set.

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Wax, paper, bitumen, cotton, high voltages - what could possibly go wrong?


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 Post subject: Re: Contrast and Brighness
PostPosted: Sep Tue 08, 2020 6:34 am 
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Joined: Mar Sun 22, 2020 5:56 am
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Location: Arvada, CO
zeno wrote:
Oh boy a bomb tosser !
IMHO brightness sets the brite to a comfortable level for the room light.

73 Zeno 8)
LFOD !

+1. The brighter the room, the brighter the picture is needed, the more the contrast.

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Electronics are filled with smoke. It’s my job to put the smoke back in when they fail.
Cheers,
Jay


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 Post subject: Re: Contrast and Brighness
PostPosted: Sep Mon 21, 2020 6:21 am 
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Posts: 4642
Location: Lincoln City, OR 97367
Brightness = CRT average beam current adjust.

Contrast = video gain.

Regards,

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Jim T.
KB6GM


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 Post subject: Re: Contrast and Brighness
PostPosted: Sep Mon 21, 2020 9:04 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 1149
Location: Belrose, NSW, Australia
Quote:
Brightness = CRT average beam current adjust.

Contrast = video gain.

That's only valid for AC coupled video, i.e. the bulk of US B&W TVs so in most cases you'd be right.

For DC coupled video and designs where the black level is restored with a clamp, "Contrast" becomes "White Level" and "Brightness" becomes "Black Level".

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Wax, paper, bitumen, cotton, high voltages - what could possibly go wrong?


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 Post subject: Re: Contrast and Brighness
PostPosted: Sep Tue 22, 2020 11:41 am 
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Joined: Feb Thu 17, 2011 11:27 pm
Posts: 14175
Location: Long Island, N.Y.
I've owned and used early TV's for decades. I find that the majority of pre-1950 models require careful synchronization of all controls to give the best picture and sound. It's almost like tweaking the controls on a '20's 3-dialer radio. Some, like the Pilot TV-37, are particularly finicky. The technology of that period required a lot of user interaction.


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 Post subject: Re: Contrast and Brighness
PostPosted: Sep Fri 25, 2020 12:46 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 813
Location: Rockaway , nj 07866
There was a 40s or early 50s owners manual for a set I had that said turn brightness up until you just see the image , then turn the contrast to brighten , that was what it said but I found if you followed that method you could end up with too much black and not enough brightness


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 Post subject: Re: Contrast and Brighness
PostPosted: Sep Sat 26, 2020 8:30 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 1149
Location: Belrose, NSW, Australia
Here's how I'd detail the process back in the day where I trained new color TV owners - normal practice in those days was to have a tech install them:

1. Turn color to minimum
2. Adjust brightness until the darkest parts of the picture just light the screen
3. Set contrast mid-way - (most TVs by then had the beam current limiter working on the contrast).
4. Adjust colour control to get realistic flesh tones (no Hue control, this was PAL)
5. If the picture is too bright, adjust it with the Contrast control. (On most TVs by then color would track contrast)

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