Contrast control – why in the middle / factory default?

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  • #35849

    Kalwant
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    Hi DisplayCal

    This application is amazing, I’ve used it many times and donated some cash previously for my appreciation.

    One question I have is regarding the contrast control. In your instructions, you state ‘Also note that for most LCD screens, you should leave the “contrast” control at (factory) default’. In Florian’s youtube tutorial, he has the contrast control at 50%.

    I have used calibration software for my TV before and they all prefer as high a contrast setting as possible before the ‘blooming’ of lines in test cards.

    Why is it that in DisplayCal it’s recommended that the contrast setting is 50% or the factory default? Wouldn’t I be able to get a better contrast ratio if it was around 75% etc?

    Thanks!

    Kalwant

    #35854

    Patrick1978
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    The contrast control on LCD monitors will usually clip whites if increased over the default value.  You do that on a TV because the standard video signals go from 16-235 instead of 0-255 like the signal a computer will send to a monitor, so for a TV you adjust the contrast so that 235 gets adjusted to 255 properly.

    For computer monitors contrast generally shouldn’t be touched unless the manufacturer didn’t set it up properly.

    Go find a black and white gradient image or create one yourself and turn up the contrast on your monitor and very likely all the light gray becomes a solid block of full white because those levels are getting clipped.

    #35855

    Kalwant
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    Patrick1978, thanks for your detailed reply! I’ll try what you said with a test card just for fun.

    Is there a way to find out what the default contrast value is on a monitor? Is it always 50% / in the middle or could it differ?

    • This reply was modified 1 month, 2 weeks ago by Kalwant.
    • This reply was modified 1 month, 2 weeks ago by Kalwant.
    #35858

    Patrick1978
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    It varies depending on the monitor.  Some will default to 50%, 75%, or 100%.

    Generally the default value in the default picture mode is the native contrast setting.  Some monitors have different picture modes that have a non-default contrast setting.  It’s almost never a good idea to use any of those modes anyways, but certainly not if you are doing a calibration since those modes often lock out some settings.

    The contrast setting is kind of a throwback to CRT displays where that actually controlled the max brightness by changing the voltage to the electron guns, while the brightness control on CRT’s actually set the black level by adjusting the minimum voltage.  On LCD’s the contrast control is more akin to opening an image in photoshop and playing with the levels.  You can’t actually make it brighter since an LCD’s brightness is controlled by the backlight but it can look brighter by clipping the whites.

    #35864

    Kalwant
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    That’s great knowledge Patrick1978. I like to understand what happens under the bonnet. Very interesting.

    #35913

    Raj S
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    To measure clipping, I recommend using either HCFR’s Near White luminance graph or ColourSpace’s Clipping graph.

    With that I discovered that my monitor’s default contrast 70 was fine, but it could go up to 75 before it started clipping. It’s just that gamma, grayscale and white points were optimized for contrast 70 out-of-the-box. My monitor had headroom for contrast but most others usually don’t. That’s why you want to keep contrast at factory default.

    #35914

    Kalwant
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    Thanks Raj, useful to know and interesting.

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