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Esta demonstração apresenta uma comparação entre a codificação JPEG 2000
e a codificação JPEG "convencional". Ao contrário de outras demonstrações,
poderá verificar que é feita uma tentativa de ser tão objectivo quanto possível.
Com a codificação JPEG convencional, a utilização de um factor de compressão
demasiado elevado causa artefactos indesejáveis, tais como
With conventional JPEG encoding, applying too much compression will
cause very undesirable artefacts, such as harsh boundaries between different
areas of colour, visible blocks, and fringes around edges.
Rather than compress so hard, a good way to reducing these artefacts is
to reduce the overall image size before compressing it
- the easiest thing to do is to halve it in both dimensions. JPEG
compression then has to be far less abrupt to get to the same
target file size - providing the image can then be enlarged up again
to the original size. This works particularly well if the resulting
image uses interpolation rather than replication to put back the missing
pixels!
The following screens allow you to compare parts of several high quality
test images to compare the effect of fairly severe amounts of JPEG and
JPEG2000 compression. You will need a later version of a browser,
capable of supporting embedded PNG. We recommend
Netscape Communicator V4.7. All images are transmitted as PNG to
avoid further distortion. Please note that the full size images vary
from 200 Kbytes to over 2 Mbytes in size, before you start to look at them!
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