Using Scopes and Color Corrector Wheels

requires Vegas version 4

Before and after images after applying correction using color curves and color corrector filters. While you could get the same results in earlier versions of Vegas, you can do it easier, faster and with more accuracy using version four.

The Histograms below show the relative distribution of the pixels making up your image which can be altered by using the Color Curves filter. This allows you to redistribute the various pixels that make up any image. Note that if you could blow up the Histogram to giant size, it would be a bar chart with 255 individual vertical bars each representing the strength of the combined RGB signal at any given position of any frame in your video. You can display various charts that show individual graphs for each color, but that's beyond the scope of this tutorial.

With the Histogram running in real time you can clearly see the relative strength of the pixels in the image at any point along the vertical axis. The higher the peaks the more luminance the image has at that point. If you activate the scopes feature, the Histogram and other scopes will update in real time with the Histogram graph changing its shape both vertically and horizontally.

The peaks on the vertical scale indicate how many pixels are present at that point. The more to the left the overall graph is positioned, the more pixels there are in the shadows. The more to the right or higher values approaching 255, the more pixels are in the highlights range of the picture. Ideally, most videos have a fairly equal distribution with neither too few or too many pixels on one side of the graph or the other. Very dark images by their nature will have far more peaks represented on the left side of the graph, while very bright images will have the majority to the right. The graph will change along the horizontal shrinking and expanding in real time indicating how the pixels in you video are distributed.

 

With this knowledge you can alter where on the scale the pixels are distributed, thus correcting washed out or too dark videos rather easily. Few videos will have a distribution across the entire horizontal axis. So it is fairly common to have low peaks, sometimes none under 60 or over 230.

Note that along the horizontal axis the histogram from the original image is narrower indicating a fewer pixels in the shadows or darker parts of the image as well as lacking pixels in the higher highlight regions. By applying the color curve filter, we have flattened out the distribution somewhat and caused more pixels to fall into both lower and higher regions. This adjustment boosts contrast and saturation without adversely disturbing the midrange values as applying the brightness and contrast filter would have because it would effect all pixels in the image a like amount. By using Color Curves, (the actual "S" curve used is at bottom of this article) we have far greater control over which pixels we apply adjustments to.

 

Once you adjust the distribution of pixels with color curves, you can move on to adjust levels and gain and make color balance adjustments. In earlier versions of Vegas you had to use multiple filters. In version four, everything is combined with the new powerful Color Corrector filter. You can of course if your wish just adjust the colors manually and get good results. You can also let Vegas be more interactive.

As a first step I like to tweak both Gamma and Gain levels, make a rough adjustment without regard to looking at any Histogram. Originally the value were a little different then show at the left.

Note that there are three colors wheels, the leftmost or wheel labeled low should be used for what falls n the shadow area, the middle wheel for midtones and the high labeled wheel for adjusting highlights.

The color corrector filer can act in a similar way to what I explained in my Tutorial Three, Color Adjustments by the numbers. Note that under each Color Wheel there are two eye dropper icons. The left one under each color wheel can provide a complementary color hue without you needing to do any calculations.

Begin by clicking the complementary color eye dropper under the Low Color Wheel. Drag it over the image in the preview window. It is assumed you already moved a typical frame into the Preview Window. Click it on a dark area like the man's pants. You'll see the values in the Low color wheel change from their zero defaults to an angle of 166.0 and and magnitude of 0.128. Notice the change in the image colors. Where you click is important! Try for a representative color. Avoid absolute blacks and absolute whites if possible. Aim for something a tad less in each case. Note how the colors in the darkest part of the image have changed once you click in the Preview window. If you're not happy with the results, hit the undo button on Vegas' menu bar and try again. Keep in mind your final results depend on adjusting all three wheels. So until you do the image won't look right yet.

Now repeat using the complementary color eye dropper for High, I clicked on the man's shirt. Again the values on the Color Wheel and the tones in the highlight region of the image change. By this time the image is should be fairly well corrected color wise, because we had both pixels close to black for lows and to whites for highlights to work with. To adjust midtones, especially if you have human subjects in the scene you're probably better off slowly adjusting the Mid Color Wheel manually. The original looked a little cool, so I warmed it up by moving the midtones on a diagonal towards Y1 and R to add both yellow and red tones to get the hair and skin tone as I wanted.

Don't be afraid to manually nudge all the wheels after you used the eye dropper. Or just type in slightly different values in the boxes provided until you're happy with the hue.

Now look again at the two Histograms. Notice how the bottom one is more spread out and has lower peaks. While the Color Curve Filter had the most effect, changing the Gain and Gamma values slightly also can adjust the position of the peaks on the horizontal axis. This is more of a value judgment. Much depends on the video you're adjusting, what if anything you know about the true colors when the video was shot plus taking into account the lighting and how the video will be viewed in its final form. This tutorial because you are viewing it off a computer monitor and looking at a web page looks somewhat different than it does on a external monitor connected via firewire. Important to remember when you're making these kind of adjustments. Unless you plan to only viewing your video on your computer be sure to use an external monitor or all your work adjusting is for nothing.

Final Tips: For best results you need to shift your focus from the view on the external monitor to the Histogram and Luminance waveform which is the right most chart in the above screen shot. Note that it has a scale of 120 to minus 20. Look closely at the before and after views. In the original the waveform is concentrated mostly between the range of 20 and 60. If you look closely at the after waveform you'll see a change in the pattern with more pixels in a higher range. By carefully making minor adjustments alternating between Gamma and Gain you can center the waveform on the horizontal in the bottom Histogram while watching the vertical shift in the upper wave form. Just keep the Gamma and Gain settings so that no part of the waveform gets above 110. Somewhat less, like a 100 is probably better for most videos. You can also use the offset slider to add or subtract the the luminance. This control is super sensitive, a little movement goes a long way. Rarely would you want to go much beyond a plus/minus twenty. Remember also that the Gain and Offset work interactively.