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Levels: The Key To Contrast And Detail

Display Calibration 201: The Science Behind Tuning Your Monitor
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We’ve established that dynamic range is the most important element in image quality. Just like audio, the greater the difference between the extremes (soft and loud, light and dark), the greater the realism and sense of depth. And in a rare bit of good fortune, this is the one thing a user can achieve with a monitor that doesn’t require a meter or fancy software! What we’re talking about are black and white levels, or, as they’re more commonly known, brightness and contrast.

At some point in history, a not-so-clever television engineer decided that the controls affecting dynamic range should be called brightness and contrast rather than black level and white level. This has created confusion as to what these adjustments are actually for. It’s actually quite simple, though. Brightness is black level and contrast is white level.

Now, what are we doing when we change those controls? Black level/brightness refers to the minimum level of light a display will produce. White level refers to the maximum level of light. Obviously, by minimizing black and maximizing white, you'll achieve the highest contrast ratio and the greatest dynamic range possible for a given display. The trick is to set the levels properly, while retaining all of the image's detail.

To illustrate the importance of setting black and white levels correctly, let’s check out an actual photograph. We modified the original in Photoshop by using the Levels dialog to manipulate the black and white levels. This is functionally the same as adjusting the brightness and contrast controls on your monitor. No adjustments were made to color.

Here’s a shot of singer Gavin Rossdale performing with Bush.

This is a pretty detailed photograph. You can clearly see the definition in his arms, his hair, and his jeans. Plus you can see the audience far in the background. And check out the subtle outline of his right hand against the guitar’s body.

Here’s the histogram.

Nearly the entire brightness range is represented, except for a few steps at the dark end. And there are one or two steps at the bright end that get crushed. This image is straight from the camera with no post-processing.

Here’s the same shot with the black level set too low.

The audience and Gavin’s hair get obliterated. His right hand now blends into the guitar’s pick guard. And his jeans have far fewer wrinkles than before. This is what we mean when we use the term crush or clip in reference to black. The darkest information is crushed together and shadow detail is lost. Where there were perhaps 50 gradations of black, there is now only one. While an artist may purposely modify an image like this for extra impact, the fact is that some of the original information was lost.

Now let’s see what happens when you set white level too high.

Gavin’s face and right arm turn into formless white shapes, and we lose the dimension we saw in the original. The many shades of white that created detail in his face are now blended together. Since the audience in the background is also brighter, the sense of depth is significantly reduced. It’s harder to tell just how far away they are.

Here’s the same photo with the black level set too high.

You can still see the detail, but now there’s a hazy look to the photo, as if a filter was put in place. Any sense of image depth is drastically reduced.

Our final example shows the effect of setting the white level too low.

Again, the detail is all there, but the photo looks dim and underexposed. This and the previous image retain all of their detail. However, by reducing the dynamic range, the vibrancy and impact are significantly lower.

We’ll show you how easy it is to fix these problems with a couple of test patterns you can download from the Internet. Setting black level and white level properly doesn’t require instruments or software. And it’s one of the best things you can do to improve your monitor’s image. By maximizing dynamic range, you’re well on your way to better pictures!

To fully take advantage of a display’s dynamic range, we also need to understand what’s happening to the points in between black and white. This is where the discussion turns toward gamma.

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  • 8 Hide
    expl0itfinder , October 13, 2013 9:31 PM
    Interesting article. Very detailed and well written. Kudos to the author.
  • -4 Hide
    MANOFKRYPTONAK , October 13, 2013 10:25 PM
    For TVs CNET posts the color levels they use to test each TVs picture by model. They also give great advice on how to adjust too! I used there settings with my 50" vizio and could not be happier. Don't get me wrong loved this article, but you can never get too much info, am I right?
  • -2 Hide
    yolosweg , October 13, 2013 10:37 PM
    I've adjusted the gamma on my laptop but it keeps reseting. Does anyone know how to fix this? (I used the default windows program btw)
  • 0 Hide
    Vladimir83 , October 13, 2013 11:11 PM
    Fantastic article.....TomsHardware style!
    I have no idea how my monitor was off until i saw the patterns ;) 
    Now perfectly set for brightness/contrast:first,third,and fourth pattern(although on this i notice cliping on the blue).
    However second pattern couldn't set it right.Darkest bar which should be almost cliping to the background is too "black",and the next "12" bar is more closely match to the background in colour.
    Any thoughts someone? I use Philips 227Eqha IPS monitor.
  • 2 Hide
    rezzahd , October 14, 2013 8:08 AM
    Great display calibration guide. I would recommend this to anyone new to display calibration.
  • 1 Hide
    clonazepam , October 14, 2013 10:48 AM
    Every time I took a support call for pro graphics products, and it centered around getting accurate color, I started off with "Color is a 3-dimensional space..." It was just my way of saying we might be here for awhile.

    I love these articles. =)
  • 0 Hide
    ojas , October 14, 2013 11:19 AM
    Second page, second last photo, article should say that you've set the black level too low, not too high.

    Seems to be an interesting read so far, and I've really wanted to read an article like this, so thanks in advance!
  • 0 Hide
    ojas , October 14, 2013 11:30 AM
    Doesn't the first picture of Gavin on the 3rd page have low gamma and the second bright one is where the gamma is too high?

    It's written the other (incorrect?) way around in the article, i think.
  • 0 Hide
    ojas , October 14, 2013 11:56 AM
    Quote:
    Now we’ll make the color temp too warm; in other words, below D65.


    Shouldn't it be "above D65"? :/ 
  • 0 Hide
    gwolfman , October 14, 2013 1:04 PM
    Quote:
    Doesn't the first picture of Gavin on the 3rd page have low gamma and the second bright one is where the gamma is too high?

    It's written the other (incorrect?) way around in the article, i think.
    It's opposite. Lower gamma makes the dark areas of an image brighter, hence the entire picture looks brighter. Higher gamma makes the lighter areas darker (i.e., it takes a lot brighter white in the image data to actually be displayed white). Check here for a great tutorial on gamma, especially the section titled "Display Gamma."
    http://www.cambridgeincolour.com/tutorials/gamma-correction.htm


    Quote:
    Quote:
    Now we’ll make the color temp too warm; in other words, below D65.
    Shouldn't it be "above D65"? :/ 

    That's incorrect. It actually works backwards/opposite from what one might think. Color temperature originates from the color a flame radiates in relation to the temperature at which it burns. Think back to grade school and playing with the Bunsen burner... the hottest part of the flame (i.e., higher Kelvin) is in the darkest blues, not the reds (i.e, lower temperature/Kelvin). This simple picture helps explain the difference.

  • 0 Hide
    Fokissed , October 14, 2013 1:08 PM
    Quote:
    Quote:
    Now we’ll make the color temp too warm; in other words, below D65.


    Shouldn't it be "above D65"? :/ 


    Warm (reddish) colors are below 6500K, whereas cool (bluish) colors are above 6500K.
  • 1 Hide
    PhilFrisbie , October 14, 2013 1:10 PM
    Quote:
    I've adjusted the gamma on my laptop but it keeps reseting. Does anyone know how to fix this? (I used the default windows program btw)


    Try installing a full featured driver from your video hardware manufacturer.
  • 0 Hide
    gwolfman , October 14, 2013 1:14 PM
    The author of the article stated:
    Quote:
    We always measure color gamut and luminance in our monitor reviews, even though those parameters are not adjustable in most cases.

    But don't most monitors have a "backlight" option which changes how bright the image without adjusting the contrast & brightness? This can used to effectively adjust liminance, but at superficial global adjustment level rather than a granular control. None the less, one can then put preference on the brighter or darker end depending on their use case(s).
  • 0 Hide
    ceberle , October 14, 2013 3:18 PM
    Thanks for your questions about gamma and color temperature. It seems counterintuitive to say that lower gamma produces higher brightness but that is indeed the case. The lower the value, the higher the brightness.

    Grayscale can be confusing too. As the temperature gets lower, the color is said to get warmer.

    Ojas, the photo on page 2 showing a higher black level is correct. As you raise the black level, blacks get brighter and become more gray.

    -Christian-
  • 1 Hide
    ceberle , October 14, 2013 3:22 PM
    Quote:
    The author of the article stated:
    Quote:
    We always measure color gamut and luminance in our monitor reviews, even though those parameters are not adjustable in most cases.

    But don't most monitors have a "backlight" option which changes how bright the image without adjusting the contrast & brightness? This can used to effectively adjust liminance, but at superficial global adjustment level rather than a granular control. None the less, one can then put preference on the brighter or darker end depending on their use case(s).


    Unfortunately, very few monitors have separate backlight and brightness controls. None of the screens we've covered this year (16 including reviews not published yet) have a backlight control. This kind of thing is common on HDTVs but not computer monitors and that is a shame. With brighter screens, it's really nice to be able to move the dynamic range up or down to get better blacks or brighter whites, depending on application.

    -Christian-
  • 1 Hide
    Shankovich , October 14, 2013 5:50 PM
    Another great article to put in my references, this is why I love Tom's
  • 1 Hide
    jeffredo , October 15, 2013 1:33 AM
    I just broke down and invested in a Spyder 4 Elite colormeter.
  • 0 Hide
    kevith , October 15, 2013 3:32 AM
    My monitor looks the same no matter what of this I try. And the conclusion is, as in the case of every "adjust-your-monitor-in-an-amazing-small-number-of-steps" article I ever read: Go buy the hardware thingy or forget it.
  • 0 Hide
    ojas , October 15, 2013 4:13 AM
    Quote:
    Quote:
    Doesn't the first picture of Gavin on the 3rd page have low gamma and the second bright one is where the gamma is too high?

    It's written the other (incorrect?) way around in the article, i think.
    It's opposite. Lower gamma makes the dark areas of an image brighter, hence the entire picture looks brighter. Higher gamma makes the darker areas even darker (i.e., it takes a lot brighter white in the image data to actually be displayed white). Check here for a great tutorial on gamma, especially the section titled "Display Gamma."
    http://www.cambridgeincolour.com/tutorials/gamma-correction.htm


    Quote:
    Quote:
    Now we’ll make the color temp too warm; in other words, below D65.
    Shouldn't it be "above D65"? :/ 

    That's incorrect. It actually works backwards/opposite from what one might think. Color temperature originates from the color a flame radiates in relation to the temperature at which it burns. Think back to grade school and playing with the Bunsen burner... the hottest part of the flame (i.e., higher Kelvin) is in the darkest blues, not the reds (i.e, lower temperature/Kelvin). This simple picture helps explain the difference.



    Quote:
    Quote:
    Quote:
    Now we’ll make the color temp too warm; in other words, below D65.


    Shouldn't it be "above D65"? :/ 


    Warm (reddish) colors are below 6500K, whereas cool (bluish) colors are above 6500K.


    Quote:
    Thanks for your questions about gamma and color temperature. It seems counterintuitive to say that lower gamma produces higher brightness but that is indeed the case. The lower the value, the higher the brightness.

    Grayscale can be confusing too. As the temperature gets lower, the color is said to get warmer.

    Ojas, the photo on page 2 showing a higher black level is correct. As you raise the black level, blacks get brighter and become more gray.

    -Christian-

    Thanks for clarifying that! I even changed gamma on my monitor to see what happens before i posted, i guess i misinterpreted what was happening.
  • 0 Hide
    Christopher Shaffer , October 15, 2013 12:25 PM
    This is all very interesting and I was excited for a basic how-to until you suddenly said "now get out your meter" but didn't tell me what kind of meter and didn't give me a "parts list" that I'll need to follow your guide.

    That would be very useful, along with some recommendations of affordable "meters".
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