.png)
Color Curves
This transformation lets you adjust the color curves of an image. Using color curves you can alter each of the three components that make up a color image using the HSV, HSL, or RGB color model. This lets you adjust the hue, saturation, and brightness of an image all in one operation. Or you can adjust its red, green, and blue channels independently.
The color curves dialog is resizable; the larger you make it, the larger its curve control (see below) gets. The color curves dialog has the following controls:
Amount
The amount control lets you control how much of the color curve transformation is applied to the input image. You can apply a percentage of the transformation to the entire image, or you can specify an amount mask to restrict the effects of the transformation to only part of the input image.
If the input image is color then this control lets you select whether you want to work in the RGB, HSV, or the HSL color space.
According to the color space you select, you can further select which of the three components you wish to work on. For example, if you choose the HSV color space, then you can switch among the H, S, and V components. Each component has its own curve and can be adjusted independently of the other two. When you apply the transformation to the input image, each of the three components is modified according to its own curve.
In the RGB color space, you can adjust the individual red, green and blue channels, or you can select All which displays a combined histogram and applies the same curve to all three channels.
The Curve Control occupies the entire bottom part of the color curve dialog.
Hue Curves
When you are modifying the HSV or HSL hue (H) component, things work a little differently than for saturation or brightness.
Since hue is circular, it starts and ends with the same color (red). Therefore, hue curves wrap around from the right hand to the left-hand edge of the graph. The first and last points on the curve are actually the same point, so when you adjust one the other moves at the same time. Also these two points are fixed at red and can only move up or down and not left or right.
Unlike brightness and saturation curve, hue curves represent a change in hue, not the hue value. The no-change curve is a horizontal line through the middle of the graph called the zero-line, rather than the more familiar diagonal line from lower left to upper right. Where the curve lies above the zero-line, hue is shifted to the right -- where the curve is below the zero-line hue is shifted to the left. The further the curve lies above or below the line, the further the shift. The following example of a hue curve applies a hue shift to orange pixels in the input image which shifts them to the right, towards yellow and green.
.png)
.png){kind=small}
Base Histogram on Masked Area Only
The curve control displays both a histogram and a curve. If this button is raised, the histogram is based on the entire input image. If depressed, the histogram is based on just the currently masked area as defined by the amount mask. If there is no mask, the histogram is based on the entire image. If there is a mask but it is entirely black, the histogram is not displayed. Changing this setting only affects the way histograms are displayed and has no effect on the output image.
If you are using a mask to limit the action of the transformation to just part of the image, this control lets you see the histogram of just the part you are adjusting.
Settings Menu
Load Color Curves -- lets you restore a previously saved set of color curves for application to the same or to a different image. You can import Picture Window curves (with the file extension .cc), Photoshop Curve files (with the file extension .acv) or Photoshop map files (with the file extension .amp), depending on the File Type you select.
Save Color Curves -- lets you save the current color curves in a file for later use.