Composing Digital Images With ColorBender
Presented by video conference at CUNY, NYC, on 4/28/2006 by George Dalke, Palo Alto.
Introduction
Image composition is used to attract the viewer's attention to certain objects and areas. The following painting by Bernard Londinsky, appropriately called Composition-de-fruits-et-coquillages-bois, shows many of the techniques of composition. In this image, one can easily see the effective use of brightness, contrast, colorfulness, texture and sharpness.
http://www.dicart-net.fr/photos/LONDINSK/amg0000.htm
ColorBender can selectively apply its operations to any combination of regions, colors and neutrals. Consequently it is extremely effective for composing digital images.
This presentation is organized as follows.
- The vocabulary used by ColorBender to describe selective operations.
- The basic tenets of composition, and how they are used in ColorBender.
- Several examples showing the application of these techniques.
The vocabulary used with ColorBender describes objects and operations in terms of the visual effects they produce and the visual changes that are intended. It also adopts the artist's model of tints and shades to describe tone changes.
This is unlike other image processing applications that base much of their vocabulary on historical conventions, image processing technical jargon, the physics of color and light, and, finally, the physiology of the eye. While these are technically interesting, they do not readily translate to what you see and what you want to do.
The ColorBender vocabulary consists of
- Colors
- Neutrals
- Tones
- Regions
The colors and neutrals used in ColorBender are:
- Colors = (red, yellow, green, cyan, blue, magenta)
- Neutrals = (white, gray, black)
Color tone is based on tints and shades, explained in the following diagram.
Color tone is any combination of white, black and the pure color. An example of the tone diagram in the Munsell color systems is shown below.
http://www.learn.londonmet.ac.uk/packages/synthlight/visuals/chapter1/munsell.html
The tone planes of other color systems are shaped and labeled differently. Yet, in each of these systems, mixing white and black with a pure hue to obtain intermediate tones is a valid visual concept.
A part of composition is the correct placement of objects of interest. The following example follows the "rule of thirds" placing the point of interest on one of the four key points.
The standard names of the columns and rows are shown in the following figure.
left center right top
middle
bottom
As an example, the region described by the "bottom row and middle right" should be easily understood.
The region around one of the "rule of thirds" key points is called a quad since it has four cells. The following figure shows the "top left quad."
left center right top
middle
bottom
In the above graphic of the girl, she is positioned in the top left quad and is viewing the top right quad. When composing, one might decide to enhance her, or, rather, what she is looking at.
The color bender selectors are shown in the following figure.
These buttons can be set to any pattern of regions, colors and neutrals and, subsequently, image operations will be restricted to those selections.
Since there are 18 buttons, the user can set 2^18 or 262,143 different patterns. After selecting a pattern and applying operations, a new pattern can be selected and a new set of operations applied. This sequence can be repeated indefinitely. ColorBender automatically accumulates the entire sequence of patterns and sets of operations without requiring an "apply" or "save" operation. This not only makes ColorBender easy to use, the number of possible operations is enormous yet the control is precise and intuitive.
The boundaries of the selections, regardless of the pattern, are extremely smooth, so there are no visible artifacts.
The three buttons below the regions selectors perform the following operations repectively: turn on all region selectors, invert the current selection pattern, inable symmetric processing for which an operation applied to the selected region has the inverse operation applied to the unselected region. The two buttons below the color selectors perform the following operations: turn on all color selectors, invert the current selection pattern.
While describing tone is the first step, we must now establish a vocabulary for changing tones. As an example, from the above figure we have extracted the region around the color 5/10 (value/chroma).
We define the following operations to describe how the center color is changed to give the other 8 colors. Note that most imaging applications adjust two or four of these variations, whereas ColorBender adjusts all 8.
whiter lighter brighter grayer more vivid blacker darker deeper
The ColorBender slider adjusts tones on any the following four axes.
- darker - lighter
- deeper - whiter
- grayer - more vivid
- blacker - brighter
For comparison, Photoshop (TM) Hue/Saturation controls (with preserve luminance set) adjusts tone along two axes named saturation and lightness. The saturation control adjusts tone differently for each color. For example, blues change from more vivid to grayish black, and greens from more vivid to grayish white. The Photoshop lightness control actually adjusts tone along a "bent" axis from blacker to whiter.
ColorBender Tone Operations
The following is the list of the ColorBender selective operations presented in the operation popup menu. The four tone adjustment axes for colors are the 7-10 entries.
For the following example, ColorBender reduced brightness and sharpness in the bottom left region. This helps bring visual focus to the center.
For following example, ColorBender selectively adjusts brightness and texture for the middle row and uses different adjustments for the top and bottom rows. The intent of this processing is to increases the visual depth and help guide attention to the middle of the image. Notice the extremely smooth brightness variation between the bottom and middle rows. If there were transition artifacts, they would likely appear in the cloud reflections.
The original image is shown on the top and the ColorBender processed image is shown on the bottom. Also the ColorBender auto black point and auto white point were set to overcome some confused color management.
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