openslide.level-count: '2'

[Mathieu Malaterre]

On Sun, Sep 27, 2015 at 12:44 AM, Benjamin Gilbert <bgilbert at cs.cmu.edu> wrote:
> On 09/22/2015 02:56 AM, Mathieu Malaterre wrote:
>> On Tue, Sep 22, 2015 at 8:36 AM, Benjamin Gilbert <bgilbert at cs.cmu.edu> wrote:
>>> In general, OpenSlide does not synthesize intermediate levels; we try to
>>> deliver the information actually present in the slide file, and leave
>>> the post-processing to the application. (There is one driver, hamamatsu,
>>> which does synthesize levels due to some quirks of the format.)
>>
>> Tiles are Progressive JPEG ?
>
> Hamamatsu VMS has two levels, consisting of one JPEG each.  (If the
> slide hits the 16-bit limit in width or height, level 0 is divided into
> several JPEGs.)  A "tile" is a run of MCUs between two restart markers,
> so tiles are e.g. 4096x8 pixels.  There's an index file giving the byte
> offsets of a subset of the restart markers.
>
> Since substantial downsampling is necessary for this format, and because
> OpenSlide has access to a format-specific performance optimization that
> is unavailable to the application -- scaled decoding through libjpeg --
> OpenSlide performs the downsampling in this case.

Thanks for the explanation ! I had seen the fuzzy search for restart
marker but did not know what it was for.

-M