lossless compression of still images - recommendations?

[Colin Law]

On 18 February 2017 at 22:43, Karl Auer <kauer at biplane.com.au> wrote:
> On Sat, 2017-02-18 at 21:11 +0000, Colin Law wrote:
>> On 17 February 2017 at 21:11, Robert Heller <heller at deepsoft.com>
>> wrote:
>> >
>> > Use tar+bzip2.
>> I thought that the OP meant that he wanted to compress the series of
>> images, making use of the fact that they are little changed from one
>> image to the next. Much like video is stored.
>
> Because the images are very alike, they should compress exceptionally
> well. That's kinda how modern compression works; it looks for recurring
> sequences in the data and replaces them with a index numbers
> representing those sequences. It stores the sequence once, and the
> index many times. Multipass compression looks for metasequences and
> does the same with them.
>
> I think the OP will get better compression out of tarring them up
> first, then compressing them, because that lets the compression program
> look for sequences across the whole set, not just within one image.
> However, it would be worth trying both (compress first and tar first).
> It would also be worth trying a few different compression programs.

Yes of course you are right, I had not considered the fact that
compressing the tarred fileset will detect the repeated patterns
across the set. I was thinking that the intention was to compress
separately, which would be less likely to find the repeats, I presume.

Colin