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, if you 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, making a rough
adjustment without regard to looking at any Histogram. Originally the value
were a little different then shown above.
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 filter 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.
