johnvanvliet

All of us have some pet peeve ,or more than just a few sometimes

mine
JPEG COMPRESSION ARTIFACTS !!!!

most of my time in digital image restoration is trying to REMOVE and undo these "cow pucks "

Now the use of jpg / jpeg image format on the net is one of those necessary evils
( like messing up the incantation Gort: "Klaatu barada n?? n something ??? necktie ," when ash picks up the Necronomicon )
--- shop smart , shop S-Mart ---


if not done well EVIL things will happen

from years and years of looking into a "grain viewer " on an enlarger easel for printing photos , one of the truths is...
-- the EYES HAVE IT --

the eye is a GREAT image to use for a demonstration

the Original image is the Kodak "k04.bmp"
http://scien.stanford.edu/index.php/...es-and-videos/
http://scien.stanford.edu/images/labsite/k04.bmp

using the Eye is the FIRST point i look for focusing a image in an enlarger and it REALLY shows the jpg lousy compression artifacts
the jpg format is called a lousy format because the compression IS NOT DATA LOSS LESS
you PERMANENTLY loose a ton of information in the image
-- NEVER TO BE RECOVERED !!!!

an example
most people tend to do this
1) save a jpg from the web
2) make a small edit and RE-SAVE it as a jpg
3) make a second small change and RE-SAVE the RE-SAVED jpg image as a jpg

5) at some point you realize that the image now "looks HORRENDOUSLY hideous"

-- a close up of the original image

-- a jpg save image

see the squares in the second image , it looks "boxy "

now the ORIGINAL bit mapped cropped image is 3.9 Mib and the jpg image is 27 Kib and a png of this image is 1.9 Mib
there is a lot of image lost in making it only 27 kb in size

it is a small size BUT you loose a lot in doing that

so

if one MUST use the jpg format
convert it to a jpg in THE VERY VERY last step !!
the very last thing is save it as a jpg ( and NEVER!!! reuse that jpg)
also you have a level of compression
you can save most images at 96 % -- only toss out 4% of the quality and have it the same size as the LOSSLESS compressed image format
PNG

there is really NEVER a need to go below 90 to 95 % in saving a jpg