Pixellation v JPEG artefacts

The description of JPEG artefacts and the example image given in the course notes (Photography 1 Expanding your Vision, 32-3) differ slightly from my understanding of the term. In particular, the image appears to be exhibiting pixellation rather than artefacts.

This is an exercise to deliberately degrade an image in an attempt to explore the difference.

An enlarged portion of each image is presented below.

IMG_4141 orig extract

Portion of the original image. There is minor pixellation arising from the enlargement process.

IMG_4141 artefacts3 extract

Portion of image displaying JPEG artefacts. The image is broken into squares, each of which has simplified slightly but still displays internal detail. JPEG artefacts often manifest as ‘halos’ at hard edges. It is possible to provoke stronger artefacts by sharpening or levels adjustments between successive re-savings.

IMG_4141 pixellated extract

Portion of image displaying pixellation. Each 4×4 square is a single colour and detail has been lost.

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