extropolated megapixels

Hi Richard,

Welcome to Digicamhelp.

I can be wrong, but I think you meant "interpolation." If so, this relates to when you change the size of an image and it is resampled (pixel dimensions changed). Intepolation refers to the actual resampling method. Most of us don't even realize this is being done when we resize an image...the software just does it's job in the background.

Here's some information and an illustration about how an image looks after it is resampled:

http://www.digicamhelp.com/what-is-resampling/

As you can see by the illustration, the resampling improves the look of an image after resizing. Realize though, if you alter the size too much, particularly when enlarging, the resampled image can appear blocky looking, ie. pixelated.

According to Adobe Photoshop help files, "resampling refers to changing the pixel dimensions (and therefore display size) of an image. When you downsample (or decrease the number of pixels), information is deleted from the image. When you resample up (or increase the number of pixels), new pixels are added based on color values of existing pixels. You specify an interpolation method to determine how pixels are added or deleted."

^{Note: emphasis mine}

Photoshop offers three intepolation methods, and I again quote from Adobe's help files:

"Nearest Neighbor (Jagged) for the fast but less precise method. This method is recommended for use with illustrations containing non-anti-aliased edges, to preserve hard edges and produce a smaller file. However, this method can result in jagged effects, which become apparent when distorting or scaling an image or performing multiple manipulations on a selection.

(Photoshop) Bilinear for a medium-quality method.

Bicubic (Smooth) for the slow but more precise method, resulting in the smoothest tonal gradations.

I know all this seem to be very technical, but there is no simple way to explain it. To be honest, all most of us need to do is use the default interpolation method of our photo editing software. Bicubic is usually the default.

I hope the information has helped; if not, let us know.