thinking outside the box Photo Editing Basics, Part 3  Brightness Levels and Color Balance XARA TUTORIAL
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This tutorial will focus on editing the whole picture - a later tutorial will show you how to make regional changes. Below is the Photo tool with its fly out menu. We'll start with the easy slider controls in the Photo Enhance tool, so click the camera icon.   From here you can adjust the brightness and contrast, as well as the color saturation, color temperature, hue and blur or sharpness. Simply enter a value or click on the arrow alongside the function to open up the slider control. For example, if you increase the contrast, the brighter parts are brighter and the darker parts are darker and vice versa. At any time you can click the 'Compare' button on the Photo tool InfoBar to compare your changes with the original. Click it again to revert back to the current settings (this toggles between the original and current). Don't forget you can use the undo to remove the last settings, so experiment as much as you wish. However, there is a much more powerful way of viewing and manipulating brightness levels by using the Histogram and Levels feature. Select the Levels tool to open the Brightness Levels Dialog and you will see a histogram for your photo. The histogram counts the brightness levels of every pixel in the picture and draws a graph to tell you where those pixels are on the scale of dark to light. The graph looks like mountain peaks and gives you an 'at a glance' overview of the brightness levels of your picture. The left side of the histogram is dark, the right side is light, and the middle is the mid-tones. The aim is to get a histogram with a good range of shades from dark to light that matches the scene you are shooting, so a night-time shot would be heavier on the left, a landscape would be in the middle and a snowy scene heavier on the right. You also want the 'mountain' slopes to go to 'sea level' on each of the far ends of the graph. The Levels dialog works in conjunction with the brightness and contrast sliders, so you can use both sets of controls together or separately. The best way to see how this works is to look at some examples so you can see what we are aiming for.   This is a good example, you can see that the histogram has a well dispersed range of peaks touching the ground at both the black and the white ends, ie over the entire brightness range of 0 to 255.   This is a classic example of a camera doing what it thinks is right - trying to expose the large area of white so it's approximately in the middle of the brightness levels. Instead of the brightness levels being spread over a 0 to 255 brightness range they are compressed, with almost no bright pixels at all. However, this is snow and it should be much lighter than this. For this reason, some cameras have a special 'snow' pre-set where they compensate.  When you are not using the pre-set, despite being counter- intuitive, it's better to over-expose snow pictures, rather than under-expose them. You might be thinking there's so much bright white that you should under-expose, but that's wrong. By over-exposing, you compensate for the camera's tendency to over-darken large areas of bright whites.   We can fix this picture by adjusting the histogram. Firstly, I dragged the white point input (small white triangle under the histogram) to the right end of the histogram (new value 173). What this does is re-distribute the brightness levels that go from 0 to 173, right across the whole brightness range. The snow is now significantly more realistic, but the result still has too much contrast, and the subject's face is too much in shade. So I will now adjust the center brightness control (which is actually a gamma control) in this case, to a value of 1.60, which further lightens the dark to mid-tones. Note that this causes a bulge in the green levels curve (the bulge at the left end means it’s only brightening the darker shades, and not the lighter shades).   This is the finished result. The histogram now shows both the original (dark red) and the new histogram (pale red overlay) with the peak on the chart moved to the right end, which is exactly what you'd expect of a picture that's predominantly snow. The resulting picture is dramatically better. Clicking the Compare button on the Photo tool InfoBar allows you to rapidly toggle between the before and after comparison.  
auto-enhance adjust brightness contrast saturation temperature hue blur & sharpness 1 2 3
white input point
brightness (gamma)