Acuity (Edges and Textures)

Acuity operations are

• Edge, sharpen and blur
• Texture, enhance and smooth

ColorBender simplifies acuity enhancements by showing images actual size and allowing the user to set the correct resolution (ppi). The steps are:

• Set the resolution (PPI) for the intended output device. If moire is a problem, use a smaller value, and if moire is not a problem then use a larger value (this will increase the file size).
• Adjust the edges visually.
• Adjust the textures visually
  

Background

Adjusting acuity in most applications is confusing for three primary reasons.

• Properly adjusting acuity depend on the image resolution. (For these applications, the user must set the radius of the transform filter, generally measured in pixels, but the radius of the visual effect is measured in distance.)
• Filtering is used for visual enhancement but is also used to reduce aliasing and moire patterns. Invariably, one must compromise between these two purposes.
• The preview device may have different resolution than the ultimate output device, and the interactive visual enhancement and aliasing decisions don't scale properly between the two outputs. This is exasperated by the habit of "zooming in" to see pixel details. For resolution independent processing, this is not recommended

Aliasing definition: http://en.wikipedia.org/wiki/Aliasing

Moire definition: http://en.wikipedia.org/wiki/Moiré_pattern

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ColorBender Technical Solution

ColorBender automatically calculates the antialiassing filters based on the resize settings (size and ppi). (These filters may have a pixel radius up to 300 pixels. They are pre-computed when an image is open so there is no delay when they are used.)

Recognizing and eliminating aliasing problems

For this example, a 2560 x 1920 pixel digital image is shown at 4.00 x 2.67 inches and 640 PPI. The following screen shot shows what happens on a 100 PPI display without proper filtering. While the image seems to be sharp notice that the chain fence has severe moire patterns.

  
A 640 PPI image shown on a 100 PPI display. Note the moire patterns in the fence.

To correct this problem, simply set the PPI to 100, the display resolution. Notice that most of the fence moire has been eliminated. However, the image is now softer.

  
By setting the PPI to 100, the moire patterns are nearly eliminated

Edge Sharpen and Blur

As a separate operation, the image can be sharpened as shown next. The image is sharper and the moire has been increased slightly.

The following shows the effect of blurring the image. While the moire has been reduced, the image is now too soft.

By using ColorBender's selective operation capability, the left middle and left bottom regions have been excluded, and the rest of the image sharpened. This was done just two clicks and a slider adjustment. Notice that the part of the fence in the center was not smoothed since it is in the same region as the face.

Texture Acute and Smooth

Texture adjustments do not effect edges significantly. For the following two examples the chain fence is only effected slightly. Compare the detail in the hair on the next two images to understand the difference between acute and smooth texture.

The texture in this image has been over adjusted to show it's characteristics. First, the texture has been smoothed without blurring the edges. This smoothing is very effective at reducing image noise.

ColorBender 1.1 is a Universal Application that runs on Mac OS X 10.4 or later

© 4G Color 2005, 2006, 2007 all rights reserved, Website updated March 7, 2007