Displaying and Modifying Rendered Images
Rendered images that you have saved to disk can be recalled for viewing and modification via the Display Image dialog ( ).
The Equalize function is used to color-correct a washed out or overly dark image. This is done by finding the highest and lowest values for the red, green and blue components of each color. Once these values are identified, an averaging operation is performed to push the high and low values to white and black respectfully. This results in a wider separation of dark to light areas in the image.
Similar in operation to the Picture control on a television, the Gamma Correction function brightens or darkens a large portion of what is known as the middle colors of an image. This avoids changing a true black or white value to a gray value.
In general, Gamma Correction helps improve a dark image so that subtle details can be seen.
Two typical methods for working with Gamma Correction are:
- Save the image at the default gamma value of 1.0, to avoid data loss, and then enable gamma correction at display time.
- Save the image with the gamma set for the brightest media, say 1.8 for display, then adjust the value for printing.
You can set the gamma value for an image when you create a saved image. At a system level, you can set the gamma value for your display by entering a value into the Gamma Correction setting in the Preferences dialog View Options category.
The Tint function modifies the RGB value of each pixel in the image.
For instance, to "tint" an image with a touch of yellow, you would adjust the blue color to a lower value. This subtracts blue and reveals its complement — yellow. Setting red, green or blue to zero causes that color to be removed from the image. This also causes the complement to that primary color to dominate the image.
The Negate function converts an image into its negative or color complement. This function is especially useful for enhancing dark grayscale images where details are easily lost in the black background.
The Blur function minimizes jagged edges by creating a smooth transition between adjacent pixels.
All images are organized by their resolution and their color depth. Color depth refers to the number of bits assigned to each pixel in the image. The more bits, the larger the number of colors that can be represented. Promis.e can be used to display images with anywhere from 1 bit of color (black-and-white) to 24 bits of color (also known as "true" or RGB color).
The Color Mode function is used to adjust an image's color depth either up or down. This means you can take an image that contains 24 bits of color (representing 16.7 million possible colors) and reduce it to black-and-white, grayscale (256 shades of gray), 16 colors or 256 colors.
In response to a request to reduce the color depth — for example, from 256 colors to 16 — the image is dithered. This is a method by which adjacent pixels are modified in color to approximate the previous value of the center pixel. This is similar in function to how magazines produce color on the printed page.