"Jpegpixi" is short for "JPEG pixel interpolator". The intent of the
program is to interpolate pixels in JFIF images (commonly refered to as
"JPEG images"). This is useful to correct images from a digital camera
with CCD defects. For example, if one pixel is always bright green, this
pixel can be interpolated away with jpegpixi.

Jpegpixi is unique in that it tries to preserve the quality of the JFIF
image as much as possible. Usual graphics programs decode JFIF images
when they are loaded, and re-encode them when they are saved, which
results in an overall loss of quality.  Jpegpixi, on the other hand, does
not decode and re-encode the image, but manipulates the encoded image
data (known as the "DCT coefficients"). Therefore, the blocks (typically 
8x8, 8x16, or 16x16 pixel areas) which contain the pixels to be
interpolated are minimally disturbed, and other blocks remain
pixel-by-pixel identical to the original image.

WWW: http://jpegpixi.sourceforge.net/