Is lossless image compression the expected default for image APIs?

[Simon (der_smon)]

Hello everyone,

I was wondering if the assumption is correct, in order to decide on how to setup the defaults for the Elixir/Erlang library we are working on.

Regards

Simon

[Andrew Hankinson]

Depends what you mean?

For the source files, it varies from raw, uncompressed, lossless TIFF, to TIFF with JPEG compression. For JPEG2000, it can also vary from lossy to lossless, but at least the container and the image format are (mostly) the same. Most servers auto-detect the input file format and react accordingly, though, so I'm not sure what the "defaults" are that you want to set?

For the delivery, the only real choices are JPEG, PNG, or WebP, so it's likely that it's a lossy format.

-Andrew

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[Simon (der_smon)]

Ah, sorry: I meant the response images. I realised that my bitonal webp images had quite a number of grey pixels because of the lossy compression and wondered if that is considered acceptable as the default.

[Robert Casties]

On 04.08.25 16:05, 'Simon (der_smon)' via IIIF Discuss wrote:
>
> Ah, sorry: I meant the response images. I realised that my bitonal webp
> images had quite a number of grey pixels because of the lossy compression
> and wondered if that is considered acceptable as the default.

Some of the response formats like JPEG and WebP do not really support
bitonal images in the sense that all pixels are either black or white. I
think it is fine to create a bitonal image and feed it to the JPEG or
WebP encoder.

I also think the bitonal option stems from ancient times when
black-and-white images were appreciably smaller and easier to process
than full-color images -- circumstances which doe not really apply any more.

Best
Robert

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Dr. Robert Casties -- Digital Humanities Scholar
Max Planck Institute for the History of Science
Boltzmannstr. 22, D-14195 Berlin
Tel: +49/30/22667-342

[Samuel Bradshaw]

WebP also supports lossless compression, so it is possible to have a pure bitonal image (and it's generally smaller than PNG for lossless).

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