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Adjusting Shadows and Highs with the Histogram

In almost every photography related forum one read how people adjust images in the camera. The majority adjust images by entering so called "best settings", settings that would alter contrast, sharpness and other. In most cases this has been the only way to alter the jpeg file before the camera saved it to the memory card. Ironically I referred to these changes as ”small" because I question if those adjustments are really small. Most cameras let the user adjust brightness or saturation or sharpness in unit steps totaling 5 steps. These steps range from, -2 to +2, with the center position "0" and making no difference to the image. That leaves the user with 4 effective adjustments , -2, -1, +1 and +2. To my math's that means every adjustment I make will change the image with 25% for that parameter which I select. That is no small change!!

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Some of the first things I learned about image editing was not to use the brightness slider when adjusting the brightness of an image. We learned the better way was to work with Levels or Curves when adjusting brightness or contrast. The reason was that in those days the sharpness slider did not adjust al three the color channels individually and by the correct amount for each channel. Later editing packages like Adobe Photoshop, corrected this mistake. It is also important to understand at what stage of the in-camera, image processing pipeline, the adjustments are made. If the adjustments are made after the camera converted the RAW image into a jpeg file, then the potential "destructive editing" type damage to the image file is even higher. Personally I do as little as possible adjustments in the camera. I studied a few camera users-manuals to look for more information on how different cameras adjust brightness in the camera. It was clear that very little information are generally supplied with cameras. The user therefore really risk damaging the image when adjusting brightness and contrast in the camera.

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The above image illustrates what could happen when the user adjust the image brightness with approximately 20% in the camera. A typical camera type, linear brightness reduction will change the complete light spectrum in equal amounts. Photoshop Elements up to version 5 and Photoshop up to the full version, CS2 used this linear type adjustment when the user adjusted the brightness slider. Later versions of Photoshop use more advanced methods of adjusting brightness and it will not have the same damaging effects to the bright and dark areas of the image as was the case with the older versions. We are not told what method camera manufacturers use when adjusting the brightness in the camera. In addition one does not know if the adjustments are made on the RAW file or if its done on the jpeg file before saving the jpeg file to the memory card. To find more information on this interesting subject, read 123di

What will happen if the user apply this linear type brightness adjustment to an image? As you will see from the above illustration, the adjusted image did become darker. What is not clearly seen is the bright areas that turned into white and the darker areas that turned into black. When dark areas turn into black and bright areas into white then it means the image lost image data in the bright and the dark areas. In effect the image dynamic range reduced. Often people reduce the camera brightness in an effort to limit burned highlights only to find the camera then has an even smaller dynamic range.

What is the case with the Olympus E-M5?

The new E-M5 from Olympus gives the photographer access to more advanced image adjustments in the camera. It is possible to dial in an Exposure Shift when the camera is metering the image exposure plus one can do that for each of the three exposure metering methods. That means for spot or center or full exposure metering it is possible to pre-program an Exposure Shift in one of 6 steps. The advantage of this method is that it is applied to the image pipeline before recording the image onto the sensor. The Exposure Shift adjustment can be found in the E-M5 Utilities Menu (*K) under the Custom Menu.

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Up to this point we saw that one can adjust image brightness in 3 different ways. The first is the above described Exposure Shift, the 2nd method is dialing in a shift in image brightness (not preferred) and the last method is setting exposure compensation. My personal choice is Exposure Shift and Exposure Compensation. One should use exposure compensation selectively only and if possible on one image at a time only.

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In the above two images you can see a proper curves function Olympus build into the E-M5. In figure 1 no adjustment was made and in figure 2 a typical adjustment to increase contrast was made. People will refer to this adjustment as the S-shape curves. In the top right quadrant one adjust the highlights of the image and in the lower left quadrant the shadows. By upping the shadows curve the shadow brightness will increase and vice versa and the same is true for the highlights.

Those of you who are familiar with the curves function will know that it is one of the safest methods to adjust image brightness. In fact if you like to master image color adjustments, contrast and brightness then you should study the curves function in more depth. The curves functionality in the E-M5 is basic only, I hope to see it expand in the future. My advice is to really master the curves function in the E-M5. The exposure compensation button on the camera will activate the curves function and each of the two adjustment dials will adjust either highlights or the shadows. That means the photographer can adjust any of the image highlights or shadows on the fly plus these adjustments will not harm the final image.

I am at the end of this short article. I hope the information is helpful and I trust that you will be as happy as I am with the advanced functionality Olympus has build into the E-M5. Have a look at the “Basic Camera Settings” article I wrote on the E-M5. In there you will find how to setup the E-M5 for using the curves function. (I programmed the video record button to the multi function option and one of the functions is the curves function) Also see this
article.

Siegfried