December 2007 | Tips and tricks
Zooming screenshot tips
Interpolation Methods
Pixel interpolation is the process of determining a value for an unknown or new pixel, based on known, and typically nearby, pixel values. SOCET GXP supports four pixel interpolation methods for zooming and for generation of reduced resolution datasets (RSets). When selecting an algorithm for use, consider the time constraints and image quality requirements of the products to be created.
The following are the supported methods in highest complexity (slowest) to lowest complexity (fastest) order: lagrange, bicubic, bilinear, and nearest neighbor. The term complexity generally corresponds to image clarity; however this depends greatly on the raster dataset being interpolated, and the type of analysis to be performed.
Guidelines for use:
- Lagrange provides the best overall and best zoom-in quality
- Bicubic is a good choice when zooming out, but upon zooming in, the smoothing tends to blur the image
- Bilinear is a good option to use instead of the bicubic method if smoothing becomes a problem
- Nearest neighbor should be used for speed and performance only, as the quality results in rough, staircase edge artifacts
- Since bilinear is hardware accelerated, it provides good performance and decent quality
- The size and shape of a feature in the image does not matter, use any interpolation method
- For panchromatic or multispectral images, use any interpolation method
- For SAR data, lagrange is ideal to use with SOCET GXP
- More artifacts are evident in images with high contrast
- RSet generation is performed once, therefore, it is worthwhile to use a more complex interpolation method if a group of analysts will be spending time zoomed out on an image
- Zoom interpolation takes place each time you zoom in or out on an image; a faster algorithm is generally desirable
- Remember, what you see visually is a tradeoff between processing time and quality
The default RSet generation interpolation method is nearest neighbor. For better quality, change the interpolation method to lagrange for RSet generation. To set preference, from the Workspace Manager, select Tools > Preferences > Load/Unload > RSet Generation, or select b. You can also change the interpolation method from the Multiport main menu; select View > Zoom > Zoom Interpolation.
| Interpolation method examples showing zoom | |
 64:1 (1.562% zoom) lagrange |
 800% zoom lagrange |
 64:1 (1.562% zoom) bicubic |
 800% zoom bicubic |
 64:1 (1.562% zoom) bilinear |
 800% zoom bilinear |
 64:1 (1.562% zoom) nearest neighbor |
 800% zoom nearest neighbor |
| Interpolation method examples showing RSet generation | |
 Whole scene zoom - lagrange |
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 Whole scene zoom - nearest neighbor |
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