Thursday, July 24, 2014
 
 
Video-Based Tutorial: Page (1) of 1 - 09/07/11 Email this story to a friend. email article Print this page (Article printing at MyDmn.com).print page facebook
Using the Vegas Pro color scopes
Looking at the Vectorscope, Waveform Monitor, Histogram and RGB Parade By Gary Rebholz

Vegas Pro software features four sophisticated video scopes that you can use to analyze your video and gain insight into color correction filtering that you might need to do in order to achieve the best results possible. In this article, I'll talk about each of the four scopes and give you some examples of how they work and how you might use them to improve the look of your videos. To open the scopes, choose View | Video Scopes.

Let's start with the Vectorscope. In the Video Scopes window, select Vectorscope from the Scope Selector drop-down list. The Vectorscope gives you a tool with which you can objectively analyze the color in your video in a way that you can't with your eye due to the many factors that affect your perception of color. These factors include reference monitor calibration, room lighting, and more. This tool can be a critical aid in color matching one scene to another.

This scope plots two aspects of color: hue and saturation. Webster.com defines hue as "the attribute of colors that permits them to be classed as red, yellow, green, blue, or an intermediate between any contiguous pair of these colors." In other words, it's what we use to identify and put labels on colors. For our purposes, you can think of saturation simply as the intensity of the color. Over saturation makes colors look unnaturally vibrant, while removing all of the saturation from a color results in a grayscale image.

The Vectorscope shown in Figure 1 is the result of my project cursor sitting in a black frame. White pixels on the scope indicate color of various hue and saturation, except at the very center of the scope as in this example. The center of the scope represents zero saturation and no hue (no color).

 

Interestingly, the scope would look exactly the same if the cursor was sitting in a frame with various levels of gray as it does on a black frame. It would also look the same sitting in a completely white frame. In other words, it's not necessarily showing us if there is an image on the frame, but rather whether or not the frame exhibits any color hue with any amount of saturation.


This scope shows the results of a black frame of video.

Logically then, the further away from the center of the scope that the white dot (or more accurately, multiple dots as you'll see shortly) sits, the more saturated the color in your video frame. But what color does the white dot indicate?

Look at the center of the scope and then move your eye in any direction to the outside circle. The direction, or angle, at which you move your gaze indicates the hue of your video frame. The scope contains six hue targets. These represent the three primary colors (red, green, and blue) and the three secondary colors (cyan, magenta, and yellow). The center of each target represents the broadcast-safe saturation level of the color. Figure 2 shows my scope with the cursor sitting in a solid blue frame. Notice that the white dot now sits outside of the scope's 100% circle well beyond the blue hue target. This indicates not only that my frame is blue, but that it's also well beyond broadcast legal saturation. This gives me important information because I could now apply a saturation filter to my frame or use other techniques that can help me tone down the saturation of the blue.


My scope indicates that the video frame is blue and is over saturated.

Now let's look at a more real-life example. Figure 3 shows my project with the cursor sitting inside a frame of video. I've docked my Vectorsope next to the Video Preview window so that you can see both the scope and the frame of video that it's analyzing. Notice that now we have more than just a single dot in the scope. Instead, we see an array of multiple dots, each of which represents a different color in the video frame. Together, they form a distinct pattern that trends from the center of the scope generally toward the area between the blue and cyan targets. This tells us what our eyes already know: There is a lot of blue in this video frame!


You can look at the Vectorscope to analyze the color tint in the video frame.

But this also gives us information that our eyes cannot necessarily know. For instance, you can see that none of the dots extends past the color targets and this assures us that the saturation levels in this frame are broadcast legal. We could also compare the readout for this video clip to that from a different clip to see if we notice any color matching problems that our eyes might not be able to catch in the lighting we're working under.

Click PLAY or press spacebar to start or stop video

As I mentioned, you can use video filters to affect your video and see those changes reflected in the Vectorscope. For instance, Figure 4 shows my project once I've added the HSL Adjust filter, increased the saturation to the maximum, and changed the hue to give the frame a magenta tint. You can clearly see those changes reflected in the Vectorscope.


The Vectorscope clearly shows the highly saturated magenta hue that I've applied with the HSL Adjust filter.

Let's look at a more complex example. Figure 5 shows what my project looks like when the cursor sits on a frame with more colors. The Vectorscope shows at least three distinct color trends toward red, blue, and yellow and you can see how that corresponds to the frame in my Video Preview window.


Three distinct "arms" in the Vectorscope reflect the red, blue, and yellow colors in my video.

I can see by the Vectorscope that my blues are not very close to approaching my broadcast legal saturation limit and I might be able to make this video look more vibrant if the blues were more saturated. Figure 6 shows my project after I've applied the Secondary Color Corrector filter to this clip and used it to add more saturation to just my blues.


I've used the Secondary Color Corrector filter to add saturation to my blues for a more vibrant blue stripe in the sail.

Compare Figures 5 and 6 and notice that the blue stripe on the sail is more vibrant in the second picture. Accordingly, the Vectorscope shows a longer "arm" toward the blue while the other two arms toward Red and Yellow remain unchanged from the one picture to the next. Hopefully this demonstrates one way that you can use the information that the Vectorscope provides to enhance the look of your videos. If an arm extends toward the space between two color targets and you're wondering whether it exceeds safe levels, point your mouse to the Vectorscope. A Yellow circle emanates from your mouse location. Position the circle so that it intersects the center of a target and you can then easily see if any dots fall outside of the circle.

Next, let's look at the Waveform monitor. To view the waveform monitor, select Waveform from the Scope Selector drop-down list in the Video Scopes window. This tool gives you a readout of your video's luminance value. In common terms, it shows you the video's brightness levels. It can also give you information on color values if you view it in composite mode, but as we just discussed, the vectorscope gives you great color information, so typically you'll use this monitor set to the Luminance setting.

It's easy to read the waveform monitor. Looking at the monitor from left to right corresponds exactly to looking at the Video Preview window from left to right. In other words, white dots on the left edge of the waveform monitor represent the luminance values of whatever you see on the left edge of the Video Preview window. The monitor shows the luminance value as a percentage vertically. Let's take a look at an example that should make this clearer. Figure 7 shows my project with the waveform monitor directly below my Video Preview window.


The bump in the Luminance values corresponds to the brightness in the Video Preview window.

You can see that the bump in the Luminance plot corresponds exactly to the left/right position of the bright area of the video frame. In the example above, you can see that aside from the area of the luminance bump the luminance values are heavily concentrated in the lower portion of the monitor between 20% and 30%. Look at the image in the Video Preview window and you can easily see that the areas to the left and right of the streak of sunlight are very dark.

Figure 8 shows another example. Notice how the luminance values are heavily concentrated in the area between about 10% and 60%. This indicates that we have some room to play with the luminance values. We can add contrast to the clip to spread the luminance values out a bit.


The Waveform monitor shows that the luminance values are concentrated mostly between 10% and 60%.

Figure 9 shows my project after I've added a Brightness and Contrast filter to the clip and increased the contrast quite a bit. The waveform monitor shows that I've spread the luminance values out over a much wider range.


You can add contrast to your video in order to spread your luminance values.

If you look closely, you'll see the beginnings of a heavy concentration of dots at the 110% line and more at about -7%. These values are the limits of acceptable luminance values. The concentration at these values indicates that by adding contrast, I've begun to push my luminance values to the limits. As I push more values to the upper limit, I begin to "blow out" my bright areas. These areas begin to lose detail and simply turn to white. To see this, look at the detail of the waves crashing into the shore.

At the other end, of the spectrum, the concentration down around -7% means that I'm beginning to "crush my blacks." This means my blacks begin to lose detail and simply turn completely black. To see this, look at the object in the very lower-left corner of the clip.

You'll want to be very careful about overdoing this by blowing out too much brightness and crushing too much black, but in this case I felt that the overall improvement to the clip was worth a little blowout and crushing. Notice how the contrast has made the clip look more vivid and alive than it originally was.

Also, make sure to check the whole clip, not just a single frame like I have here. What looks like an acceptable level of blowout on this frame could look really, really bad on a different frame! To check the entire clip, click the Update Scopes while Playing button and play through the clip again. You can now keep your eye on the scopes as they change along with the changing video information in the clip.

This is just one simple example of how the waveform monitor can help you improve your video. Sure, I could have done this without the aid of the waveform monitor, but it was looking at the waveform that made it instantly clear that I had some room to play with my contrast settings. And using the waveform monitor as I adjusted the contrast alerted me to the fact that I was beginning to blow out the whites and crush the blacks. All useful information!

You have to be careful though, because if you concentrate too much on one scope you can make changes that cause different problems that only show up on a different scope. For example, select Vectorscope/Waveform from the Scope Selector drop-down list to show both scopes simultaneously. In Figure 10 you can see that the contrast changes I made to my video while watching the Waveform monitor have caused some real problems in my Vectorscope. Notice how far my red values exceed the Red target zone in my Vectorscope.


Contrast I added to my video while watching the Waveform monitor has caused my red values to greatly exceed the Red target zone in my Vectorscope monitor.

Next, select Histogram from the Scope Selector drop-down list. This scope, shown in Figure 11 gives you a quick look at the brightness and contrast of your video. It shows luminance values from 0, which is black, to 255, which is white and the number of pixels in your image at each luminance value (represented by the height of the histogram at each value). You can use this information to get a quick sense of a clip's exposure and contrast and to quickly compare exposure levels and contrast between two clips to see how well they might match.


The Histogram shows you valuable information about exposure and contrast.

You can see that the histogram in Figure 11 is heavily weighted to the dark values on the left with little or nothing showing in the upper range (light values) on the right. This shows that the clip may have been underexposed and might give us a clue that we could stand to add a brightness filter and perhaps a bit of contrast to this image. Adding brightness to the image will shift the entire histogram toward the right while adding contrast will spread the histogram out to distribute it more evenly. You can see this in the histogram in Figure 12 which shows my project after I've added brightness and contrast to this clip.


I've spread the histogram out more evenly over all luminance values with a Brightness and Contrast filter.

You can also set the histogram to show you red, green, and blue individually so you can get a sense of color distribution in your project. Choose the color you want to see from the drop-down list at the top of the scope. You might use the information you see for a given color in conjunction with the three-wheel Color Correction filter to, for example, remove some of the reds from the shadows or add blues to the midtones.

Finally, select RGB Parade from the Scope Selector drop-down list. With the RGB Parade monitor, you can analyze the luminance of individual RGB components of your video to get a quick look at where these colors fall within the range. You read the RGB Parade in much the same way as you do the Waveform monitor in that the waveform for each color component relates to the Video Preview window from left to right with luminance represented vertically.

Figure 13 shows my project with the RGB Parade open. It's easy to spot the bump in each waveform that represents the splash of reflected sunlight in the Video Preview window. It's also easy to see that while the reds and greens in the shot extent almost all the way to the 255 maximum, the blues fall far short of that mark. This indicates that if we want to, we have some room to pump up the blues a bit.


The RGB Parade monitor shows separate graphs for each of the Red, Green, and Blue color components in your video frame.

For instance, you could apply a Color Curves filter to the clip and change the Blue curve to raise the luminosity of the Blue. Figure 14 shows my project after I've applied the Color Curve filter in this way.


The Color Curve filter has been used to pump up the blues a bit.

Notice that the clip in the video preview window has a bluer tint to it than it did before I applied the effect (refer back to Figure 13). You can see in the RGB Parade monitor that the base of the blue curve has been lifted higher than that of the red and green curves. You can also see that I have even more room to spare and could safely bring the blues up more, but the blues begin to look quite unnatural if I bring them up too much, so I've kept the effect a bit more subtle. If I bring the blues (or any other color) up far enough, I'll exceed the 255 top end and begin to lose the details in my blues as I blow them out. The same is true if I lower a color below the 0 bottom end where I'll begin to turn the video black.

I hope this look at the video scopes in Vegas Pro software has been helpful and has given you some ideas that will help you improve the look of your next video. Before I end, I want to mention a couple very important points. First, it's critical for you to do your best to understand and verify, if possible, what happens to your video after you deliver it. Will it be compressed somehow? What will it be viewed on? Will it be broadcast? The answers to these types of questions have definite impact on the color correction steps you take in reaction to what you see in the scopes.

And finally, I am by no stretch of the imagination a trained colorist. The filtering suggestions I have made in this article are for illustrative purposes only and should not be taken as definitive solutions to the problems that the scopes have identified. My goal here was not to train you in the fine art of color correction, but rather to show you how you can use the video scopes to analyze your video. How you fix any problems you find through your analysis is a different matter entirely!

For more training resources for Vegas Pro and all of the other Sony Creative Software products, including many free tutorial videos, visit the training page at www.sonycreativesoftware.com/training.


Page: 1


Gary Rebholz, is the training manager for Sony Creative Software. Gary produces the popular Seminar Series training packages for Vegas Pro, ACID Pro, and Sound Forge software.
He is also co-author of the book Digital Video and Audio Production. Gary has conducted countless hands-on classes in the Sony Creative Software training center, as well as at tradeshows such as the National Association of Broadcasters show.
 





About Video Based Tutorials - Contact Us - Advertise With Us - Privacy Guidelines