Faster processing for estimation only

[andrews05]

Is there any possibility for libdeflate to perform even faster when we only want to know what the size would be?

Oxipng currently performs various types of evaluations using libdeflate at lower levels before performing a final compression at a higher level. E.g. the Brute filtering strategy compresses a small portion of the image data using each PNG delta filter to work out which might be best. This is already impressively fast using libdeflate at level 1 but is naturally still a lot slower than other filtering strategies. Some mid levels are also used for evaluating transformations without keeping the result. Any chance for higher performance here would be amazing.