Advanced Color Curves

This is a untouched original image and a default Color Curve filter as it appears immediately after dropping on the timeline. With most browsers, you can right click on the first image and save it to your system, then drop it on a track on the timeline in Vegas and follow along or use your own material that has a similar problem you wish to correct The image I've selected is fairly typical in that it lacks contrast and is a little washed out. Alongside the image is the FX Color Curve filter as it appear if you drag and drop it on the timeline without selecting any presets.

The arrows point to the tangent controls (small gray square) that modify the curve. We're going to go step by step to show you how easy it is to modify specific areas of a image without adversely affecting areas that need very little or no adjustment. The most obvious problem here is the low tones or shadows need the most correction which is also apparent in the histogram and waveform if you're using version four.

If you don't add any points anywhere along the diagonal line (explained later) the tangent handle pulls the curve from the default end points at either end of the line. To adjust darker tones or shadows, position your cursor over the lower tangent handle (red arrow) and it should change to a four headed arrow. While holding down your left mouse button drag the tangent control down and to the right. Comparing the before and after image you'll note the skin tone is slightly darker but the shirt has darkened the most with the hair also picking up darker shades.

If you have version four of Vegas you can observe the changes you make in the histogram and waveform scopes. As you pull the curve around the distribution of pixels in the waveform will shift. Note that in the original waveform, far left, there is hardly any representation in the 90 to 100 range. Also notice the cluster of pixels is overly bright in the 60-70 range at the left of the waveform.

After adjustment there is an expansion in the upper area with a better distribution of pixels as shown in the corrected waveform with a corresponding drop in the 70-80 range. While its hard to see in this small an image there is also more even distribution in the lower ranges as show by the bottom red arrow if you look very close.

Using the color curve filter does not add any pixels, it just shifts their placement. This is why it is best to start with this filter unless the image is so poor more forceful adjustments need be made with levels, gamma and gain, which ideally are more useful for further fine tuning after adjusting using curves.

Changes in the curve also show up in the histogram. The more "curve" in the line the more a shift there will be along the horizontal axis in the histogram. This is the "secret" to adjusting images that are unbalanced having too many spikes in either shadows or highlights.

With just a little practice using color curves you can restore balance and frequently make dramatic improvements. In the image we used there isn't any major problem, it just is washed out and lacks contrast and would benefit from some rise in the highlight range as well to increase overall brightness.

The all-important midtone region that makes up the bulk of most images is acceptable as-is in this sample and really requires little if any adjustment. If you were to use the brightness/contrast filter you would increase/decease all pixels an equal amount thus distorting the the distribution of pixels ending up shifting the mid range either too much or too little. Because this image isn't that far off, correcting with the brightness/contrast filter would achieve similar results. However the further off the image, the more important using Color Curves as opposed to the brightness/contrast filter becomes.

Looking at the second color curve (above) you'll see the top right portion has a very minor upward curve, (note the tiny amount I pulled the top handle) the middle section now has a slight bias down and to the right or a bit in favor of shadows, while the bottom third has traveled the furthest down and right effecting the darkest shades the most.

There is no magical formula. Every image will be slightly different, but the basic steps to correct are the same. If an image is too dark, reversing the curves making them go in the opposition direction usually works well.

The red arrows in this after histogram shows the effect after the final curve adjustment has been made, shown lower on this page. I placed the after histogram under the original to illustrate how it is altered. Again because the source image isn't too far off the changes are more subtle. Note that the first two arrows point to a increase in lower ranges and a gentle softening and spreading out of the mid range area. The highlight range (third arrow) hasn't changed that much.

Next, we want to brighten the highlights a little. Position cursor over the upper tangent handle, dragging it up and to the left. This will boost the highlights. While most of the effect is in the top third of the curve, note that moving the top of the curve further to the left and in a somewhat steeper arc it also pulls the middle portion and lower portions of the curve with it. This is not a mistake, rather part of the correction process.

Without any set point or unlocking the tangents the curve moves as a unit. As you suspect that can be altered, which we'll explain in a later step. For now, we want the curve to behave as a single unit. Remember as you adjust one end or the other the more you adjust the more effect it will have on the opposite end and to a lessor extent the middle. So as you can see, I went back and pulled the bottom handle further out and now both handles are roughly the same distance out from the original diagonal line with the curve itself starting to look like the the letter "S", hence where it gets its name, "S" curve. Note that without touching any hue control and using the color curves filter exclusively, the hair and shirt after taken on more yellows and the skin has more luminance without being too red.

Now right click near the center of the curve and add a point as shown by the red arrow. Now there are two new tangent handles pointed to by the blue arrows in the diagram. Position your cursor over the center point you just created and while holding your left mouse button down very slowly drag up, down and right, left to achieve the best overall balance. As you can see I ended up a bit right and a tad below dead center. Check the histogram waveform and image for the most balance. Again I picked up a little more color in the hair and shirt, it doesn't show that well in a small web image, but is more noticeable when viewing on a external monitor.

Finish by right clicking on the center point, now uncheck lock tangents. This allows you to fine tune the top and bottom half of the curve separately. You of course can add as many points as you want anywhere along the line and adjust only a very small portion of the image. You'll mostly need to do the midtones which account for most pixels in most images.

By having the tangents unlocked they now swing on their own axis. So dragging just the top tangent control (middle blue arrow) counterclockwise you can boot highlights in all areas in a curve ABOVE the set point. Going in one direction or another pulling and pushing the tangent handle effects the slope of the curve, but only the portion about the set point. By dragging the bottom tangent control (bottom blue arrow) you increase/decrease shadows dragging the bottom half of the curve without effecting the the top half of the curve. If necessary the top end of the curve (right most blue arrow) can be pushed in a steeper arc adjusting the brightness, likewise for the bottom tangent control to make adjustments to the darkest shades. So the starting end points of the curve extreme top and bottom can be shifted as well. After all that pushing and dragging, you may find that a slight nudge in one area or the other while watching the image, histogram and waveform gives the best overall result.

Before and after. While the various steps are a little tedious the first few times you try them, soon you'll think nothing of the process and adjust color curves in a manner of a few seconds or so. After a time, you'll also develop a sixth sense and indistinctively know pretty much what type of curve is necessary. You may find it helpful to save as a preset custom curves you make, then you can drag and drop the custom color curve preset to the timeline and probably make good adjustments with just minor tweaking not needing to go through all the steps from scratch.

OK, now the image is well balanced and we're ready to do the next step, more finely adjust the colors. For that we'll use two new filters in version four, Color Corrector and Color Corrector Secondary to further refine the skin and hair tones. That's will be covered in the next tutorial in detail.