Graphics Reference
In-Depth Information
the top, you are saying “every source value to the right of this point should be mapped to
100.” In turn, every value along the line to the next point is also remapped.
The best way to see this visually is to load the “ramp_from_0-254” file. I created
this image in Photoshop; it has a gentle S shape to it if you look at it with the waveform
monitor. Make some adjustments to it in the Curves tool. Watch the Luminance Waveform
monitor (LUMA WFM in Color Finesse) while moving the bottom left point of the graph to
the right, straight along the bottom of the graph. Notice that the waveform flattens along
the bottom right, corresponding to how far you move the point along the Master Graph.
Also notice that in the video monitor, the amount of the ramp that is completely black has
increased. Now move it straight up along the left edge. The black level in the waveform rises
and the video monitor becomes washed out because there's no longer anything mapped
to pure black. In both cases, notice that the most extreme change, visually, is in the blacks
or shadows. The gammas move fairly significantly and the highlights don't change much.
Now do the same for the point at the top right corner of the graph, representing
the highlights. Move it down along the right edge, watching as the waveform monitor
drops along the right edge from 100 and the video monitor becomes less contrasty
because there are no longer any bright whites. Then move the top righthand point to the
left along the top edge. Notice that the image in the waveform monitor flattens along
the top as all of the values are clipped to 100. Also notice how it changes in your video
monitor. The pure white band to the right of the ramped gradation becomes broader and
broader as you move the point to the left.
For now, we will concern ourselves only with the first graph, which
controls the master level.
We'll start by determining where our black level (shadows) should be.
Looking at the LUMA WFM display, you can see that there is almost no
part of the image registering below 30IRE. You can also see that there is
significant clipping of the highlights by looking at the tight, flat line along
the top of the waveform at 100IRE. That means that we probably will not
be able pull any detail out of the sky.
Let's start with fixing the black levels first. This item is usually the first
thing that should be fixed, but it's doubly important to start with in this
instance because that's where the majority of the problem with this image
resides.
So, to lower the black level using curves, you click on the point at the
lower left corner and drag it to the right, along the bottom of the graph.
If you wanted to raise the black level instead, you'd drag the same point
straight up, along the left hand edge of the graph.
Under the graph, you can see a numerical value for your adjustment.
When you get to about 40 input, 0 output, some of the darker portions of the
waveform display start to crush along the bottom. This is where you start to
lose detail in some of the blacks. From here, the amount that you crush that
T I P
Some applications allow
you to lock the axis in
which you drag the cursor
to either horizontal-only
or vertical-only by holding
down the Shift key.
 
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