Imageworld LLC

Pixel (Picture Element)
A single unit in an electronic image. This is not simply “dot” as in “dots per inch” a Pixel is a single unit or point in an image and data as to the color of that point. Color ranges from black and white to common PC displays offering up to 32 bits per pixel or over 16 million colors per Pixel.
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Lossless
A data compression algorithm that ensures no original data is lost during the compression process, often resulting in larger file sizes. Lossless compression becomes important when post processing of data could affect data quality. A prime example is photograph enlargement. If a portion of a photograph is used to create a new photograph that is then enlarged to be the same size as the original the effect of data loss may now become apparent to the naked eye.
http://www.imageworldllc.com/document-glossary-of-terms/

Lossy
A data compression algorithm that allows reduction (loses) information during the compression process. Lost information has minimal effect on the quality of the image and/or can be recovered by interpolation from remaining data. Lossy algorithms tend to create smaller file sizes and depending upon the data (image, video, or audio) and the subsequent use or display of the data be minimally or undetectable.
http://www.imageworldllc.com/document-glossary-of-terms/