The Histogram: Maximising Your Image Quality:

Posted By @ 7:58 on April 26th 2012
Category: 101 Photographic Tips, blog, Light & Exposure, Tutorial

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Most people think the digital cameras  histogram only shows you your exposure. Few realize that it can also tell you a lot about image quality.

Some of you may have heard the saying: “Exposing to the right“ But what does it really mean?

If I told you that the histogram was a graphical representation of your digital cameras sensor and the distribution
of tones in an image you would probably reply ………“Well So What!”

But if I told you you that, by understanding how it works, you could possibly increase the image quality of your

picture by another 10-20% then that might surprize you! Digital cameras can’t see as well as the human eye. Where you and I can see up to 16 stops of light and shade,

Black & White film can see around 11 stops (see diag. below), but the digital cameras censor, (like slide film) can only see around  5 stops

The Zone System

Even if this number increases as technology advances, the theory behind how to expose an image, based on the histogram is still sound.

What you must first understand is, the histogram is divided up into five bands of equal width.  So you could suggest that each band represents one stop of dynamic range.   If these bands all recorded the same amount of information, then life might be a lot simpler, but they don’t!

Instead 50% of the tonal values are recoded in the brightest stop of the histogram. (zone VII on our diagram) half as many in the second stop and so on.

With most digital cameras recording RAW images in 12 bit, this gives us 4096 potential tonal values in an image. If 50% are in the brightest stop, that = 2048 tonal values. In Zone VI the are 1024, Zone V = 512 Zone IV = 256 and Zone III only 128

Up until now, many of us have been exposing, so our tone curve occupies the centre of the histogram as per histogram 1 on the left.  But if you want optimum image quality,  you need to push that histogram to the right in camera, to make maximum use of all that extra information as per histogram 2.

Histogram 1Histogram 2

To do this you must shoot RAW.  Focus and expose as per normal, then check your histogram.  If it looks like histogram 1 dial in a 1/3 stop using the cameras exposure compensation button.  Keep doing this until your highlight warning starts to flash on your preview image (make sure this is set to ‘on’ in the camera menu) and delete the last image as you will have burnt out highlights.

The remaining image may look washed out in your preview window,  but this can be corrected later in Photoshop.  Because there is less information in the lower values if you expose to the right you will avoid noise in the shadow areas.

Having the best file with the most information give the photographer the most choice as to how to process the image.  If you want to maximise image quality, exposing to the right is the way to go.

If you want to learn more about exposure consider taking Nigel Hicks course Understanding Light & Exposure.

These great value for money photography courses offer you weekly online video tutorials, assignments based on that weeks lesson, you upload your work for feed back from your tutor and other fellow students and you get direct access to ask some of the world top photographer questions and advice.

9 responses to The Histogram: Maximising Your Image Quality:

  1. Gramatica says:

    Very good blog and good entry. I sympathize hundred percent. I keep passing me from time to time around here to see what’s new.

    Reply |
  2. Joy says:

    Good day! I was interested to know if setting up a blog site such your own:
    http://www.my-photo-school.com/2012/04/26/maximising-your-image-quality-how-to-squeeze-110-from-your-camera-sensor/ is hard to
    do for inexperienced people? I have been hoping to develop my own blog for a while now but have been turned off because I’ve always believed it required tons of work. What do you think? Thanks!

    Reply |
  3. Julio says:

    It’s difficult to find experienced people in this particular topic, but you sound like you know what you’re
    talking about! Thanks

    Reply |
  4. Well, I’ve found that my images look best when I expose to the left, NOT the right. I adjust the shadows, and sometimes I still have to bring down the highlights, to get some detail in the clouds. Yes, there is a little more noise in a 16 megapixel image, but that noise is practically invisible, when my photos are viewed at screen size or in prints up to 20×30. I really don’t think I’d like to go back to having blown out highlights all the time, and the colors? Well, the colors when you expose to the right just look like crap. Sorry, but I know how to expose a sunset, and you CAN’T fix a sunset that is overexposed.

    Reply |
    • You want to avoid clipping the highlights at all costs. See the comparisons between histogram 1 and histogram 2 in the article above. The difference is quite subtle, what we are trying to suggest to that you increase the image data in the in the darker tones while avoiding clipped highlights.

      Reply |
  5. pc says:

    I’m increasingly shooting with jpegs which leads me to try and get things right in camera. In a sense, this is the old fashioned way of shooting. But there’s a lot of stuff on the internet about “shooting to the left” (film) and shooting to the right (digital). Frankly, with so many options (RAW, bracketing, and experience) I think too much is made of this. The end result is what counts. Pixels peepers might have apoplexy, but if you like Moriyama or Klein, or even Stieglitz or Steichen, you’ll laugh your socks off.

    Reply |
    • What we are talking about are very subtle adjustments and in everyday shooting may be unnecessary.

      But letting people know that there is more digital information in the brighter tones then in the dark ones, at least gives them the choice of knowing that if the image is very important trying to maximise image quality will mean pushing the histogram very slightly to the right.

      Reply |
  6. tch says:

    “Because there is less information in the lower values if you expose to the right you will avoid noise in the shadow areas. ”

    This is something I’ve heard for a long time but I just don’t know whether to believe it. Maybe it is true, maybe is was true and isn’t anymore, or maybe it was never true.

    With the new Sony sensors having pretty amazing low read noise this statement may once have been true but may not be now, with Sony sensors it seems shadows contain little noise while highlights blow easily, so in fact maybe we should be favouring slight under exposure?

    Reply |
    • We agree that the new camera censors are getting better all the time, but as we said at the beginning of this article they still all work in the same way.

      The fact that 50% of the tonal values are recorded in the brightest stop of the histogram, half as many in the second stop and so on.

      You will still need to push that histogram to the right in camera, to make maximum use of all that extra information as per histogram.

      Reply |

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