Image Tonality and the Histogram- Part Two: Internal Contrast

Levels HistoStarting where we left off in Part One, the darkest point on the Input scale of the histogram has a value of 0, and represents solid color or tone. The lightest point on the Histogram is assigned a value of 255, and represents no tone at all. The middle slider in the Levels dialog is referred to as Gamma, and shows the value 1.00. This Gamma number simply means that the image is presented in a linear, or numerical manner, 1.00 indicating a straight or linear relationship between the input values and the output values.

Detail is All About Internal Contrast

Your camera captures images with the potential of over 4000 tones between black and white. Once the image is captured, the camera’s job is finished. The distribution of these tones is your responsibility. Each one of these 4000 tone levels is like photographic currency. Never leave money on the table!

The following shots were captured at the lava pools on the island of Oahu. After a tricky hour-long climb down this steep lava rock hill with a full camera backpack, I realized that I had absolutely no control over the seriously-backlit scene. The light range was way beyond single exposure capacity. The detail that was evident to my eyes, was not to be found in the original images. Both the original shots were captured as JPEG images. Double-click the images to view them at full size.

HawaiiLighthouse

Out of the 4096 tones that are captured, precious few actually record the critical differences within the darkest parts of an image, and what is captured is crammed into a very small part of the tonal range. The result is that the three-quarter tones, those found between black and the 75% value almost always appear very dark and lacking in tone separation. Therefore, images that are not adjusted to unlock low-end tonality will always print dark in the three-quarter tones. Period. A non-linear tonal adjustment was mandatory with these images if they were to print correctly.

HawaiiLighthouseCorrected

Here’s where the tone distribution-monitoring histogram can be used to guide the editing process. Let’s take a new look at the histogram as a tone report. I’m gonna defy the law of common opinion here and suggest that you think of the tonal range in terms of assigned points and internal contrast ranges. Hang on here, as this will make sense after I explain it a bit further. You’ll see that Camera Raw, Lightroom, and Photoshop each provide you with ideal tools to address these very important quarter tone and three-quarter tone adjustments.

LavePoolWaves

When scene lighting exceeds the limits of a single exposure and you don’t have the luxury of capturing multiple exposures, you must rescue the quarter and three-quarter tones or lose them altogether. The only difference between these two images were careful adjustments of the White, Highlight, Exposure, Shadow, and Black sliders in Camera Raw. While I would prefer to rename these sliders, once you understand the functionality of these sliders they will allow you to “rescue the perishing.”

The shadow tones in the initial JPEG would have printed almost totally black and the highlight tones would have had no distinction if I had not developed internal contrast inside the quarter and three-quarter tones.
LavePoolWaves CorrectedWhat to do? Here’s the workflow that I use to reclaim shadow and highlight detail.

Whether you shoot RAW or JPEG format: First, open the file (from within Adobe Bridge) in Camera Raw (right-click on the file in Bridge for the option). Second, make the initial tonal adjustments within Camera Raw. All tonal and color settings can/should be performed in 16-bit space. Third, open the file in Photoshop as a 16-bit file for any further (local) editing performing all your edits using the nondestructive layer tools. Fourth, save your composite files as 16-bit, full resolution, multi-layered .psd files. Fifth, reduce the bit depth and resolution for your desired output just before you sharpen your images for final output. Save the individual output files as Level 12 JPEG (non-lossy) files. Since these files should not need to be again opened and re-saved before output, this high-level JPEG will not degrade your image and will save you considerable real estate. As you need other sizes/resolutions, repeat the fifth step.

Allow me to repeat my recommendation. I suggest that you learn to think of the photographic tonal range into specific definable points and tonal regions: shadow point, three-quarter tones, the middle tone point, quarter tones, and highlight point. This will help you understand how to control the ranges using two powerful tool dialogs found in Photoshop, Camera Raw, and Lightroom. The two main tone adjustment dialogs are Levels and Shadows/Highlights. I’ll discuss the tonal range adjustments in another post.

This series is a small excerpt from my soon to be released book titled The Digital Image: From Capture to Presentation and Everywhere In-between. If you find this series helpful, imagine what the book will do for you.

That’s the way eye sees it. Feel free to leave a comment and keep the conversation going. If you saw this post listed on a LI group page, add a comment to the listing in that group! Thanks for joining me. If you like this blog, let me know and tell your friends.

This is the first appearance of the spooky series called Image Tonality and the Histogram. This first installment is open to the public but the balance of the series will be available only to followers of this blog. Sign in now (top right of this page).

See you next time, Herb

hpaynter@imageprep.net

http://imageprep.net

Click the Follow button at the top of the page so you don’t miss any future posts.

PS. if you have an iPad and are interested in learning about more about the fundamentals of digital photography, I suggest that you take a look at my Accurate Color iBook in the iTunes Store

https://itunes.apple.com/us/book/accurate-color-audio-video/id509451372?mt=11

About Herb Paynter

I'm an author, photographer, and digital imaging consultant living in Fort Pierce, Fl. I've been in the color game for more years than I care to admit. In that time I have picked up some insights and experience that I like to share.
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5 Responses to Image Tonality and the Histogram- Part Two: Internal Contrast

  1. I appreciate your information about a subject I have found difficult to handle correctly. I learned a lot from reading both the 1st and 2nd issues. However, I am still having difficulty understanding the “What to do?” section, especially the Fifth step. How do you reduce the depth and set the resolution to correct amt.?
    Thanks for all this info. VEry informative.
    Susanne

  2. Herb Paynter says:

    Hi Susanne. Let me break this down a little for you. Editing an image in Photoshop should be done in what we call “high-bit” depth. High-bit means the image is assigned more tone steps between two colors. The more steps available, the less chance of introducing banding, or a harsh jump between tones. To get to high-bit, simply go into Photoshop’s Image/Mode menu and select 16-bit instead of 8-bit before you make major tone changes. When you are happy with how the image looks, you can go back to this setting and “reduce the depth” back to 8-bit, which is the level which your images will be printed with. 16-bit is an editing space while 8-bit is a printing space. Sending a high-bit image to a printer will cause the printing process to slow down in order to recalculate and reduce all the unnecessary pixels before it prints. Very slow process with no advantage. Sometimes the printer won’t accept these files at all!

    As far as setting the resolution goes, images intended for different uses require different resolutions. For example, high-end printing can require up to 300dpi (dots per inch) of resolution to print accurately while image that will be used only for Internet use require only 72-96dpi. Inkjet printers can deal successfully with images at 120-150dpi. Sending a high-resolution file to the Internet will result in a file that is very s-l-o-w to open while sending a low resolution file to print could result is some pretty ugly pixelation. To everything there is a purpose. If you need more specifics about this let me know.
    Herb

    • Derek says:

      Actually a file intended for the internet requires no DPI at all, as DPI is not a setting that is used by digital displays. The only thing that matters digitally is pixel dimensions, so whatever number is in the DPI/PPI field is irrelevant.

      • Herb Paynter says:

        You’re right Derek, only pixels count for the Internet. I use the dpi reference for those who are not familiar enough with pixel jargon to be able to sense the size of their image as it will appear on most monitors. If they dial in 4″x5″ at 96 dpi, they’ll better be able to visualize the size that will appear before they publish. Thanks for the clarification.

  3. naturesartky says:

    Thanks so much for the info.

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