[GTALUG] Help need in bash

[Clifford Ilkay]

>
> On 2018-06-01 10:34 AM, D. Hugh Redelmeier via talk wrote:
> * cjpeg - the IJG/libjpeg-turbo command offers easier access to JPEG
> options than IM/GM's convert, such as greyscale
>
> * you can very often have a much lower JPEG quality than defaults, but
> keep the originals somewhere safe 'cos JPEG is lossy
>
> * don't use arithmetic-coding compressed JPEGs: the browser support is nil
>
> * (almost all) JPEGs are made up of 8×8 px colour approximation cells.
> If your image isn't an exact multiple of 8 px in each direction, you're
> going to waste space in the file
>
> * consequently, cropping a JPEG can do unexpected bad things to the
> output. jpegtran — another IJG/libjpeg-turbo tool — is one of the very
> few programs that can do a true lossless crop of a JPEG file
>
> * JPEGs are for continuous-colour photographic images, and any sharp
> change in colour — like you'd get in computer-generated or line graphics
> — causes weird colour fringes / artifacts around the edges. The "modern"
> way to deal with this is to rack the JPEG quality up to 95%+ and live
> with huge files. The "right" way to deal with this is to add a *tiny*
> bit of colour noise to the image, and it will kill the fringes off.
> (JPEGs essentially store the result of signal processing the source
> image rather than the image itself. If you've ever played with signals
> (analogue or digital), sharp edges in any input waveform can cause
> "filter ringing" or unwanted harmonics in the output. JPEG fringes are
> unwanted filter harmonics, basically)
>
> * BUT … nobody really cares (or needs to) about JPEG size these days as
> every webpage is megabytes of crap anyway.
>
> * almost nobody (outside specialist domains) uses the replacement for
> the JPEG format, JPEG-2000. This is a shame, as it has some very nifty
> features like progressive viewing (so an overview will only load a small
> part of the file) and truly impressively tiny file sizes. JPEG-2000
> takes a fair amount of processing power to render (deemed too much/too
> slow for the web circa 2001) and was until recently encumbered by some
> annoying patents. Ubuntu deals with this very badly by patching a bunch
> of tools (like ImageMagick) such that when you ask for JPEG-2000, it
> gives you a JPEG. This is bad and wrong and they must get off my lawn
> forthwith.



Hugh, you reminded of this presentation I watched a few days ago. <
https://youtu.be/hQZ7Xg7q7zw>. Highly recommended.


Regards,

Clifford Ilkay

+1 647-778-8696
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