[gdal-dev] What is lost when converting 12 bit imagery to 8 bit?

[Patrick Young]

I would guess you usually see 8bit RGB images because that is what your
monitor can display.   What is lost is a deeper question, per channel you
have to squeeze the original [0 - 4095] pixel value range per channel down
to [0 -255], and there are lots of ways to do it.  The problem is sometimes
called tone mapping
<https://en.wikipedia.org/wiki/Tone_mapping#:~:text=Tone%20mapping%20is%20a%20technique,a%20more%20limited%20dynamic%20range.>.
Planet had a nice blog post describing how they manually convert their
imagery to 8bit RGB here <https://www.planet.com/pulse/color-correction/>.
If you were using the imagery for analytic things (e.g. converting pixel
values to reflectance) you'd probably not want the 8bit product.

To get GDAL in the mix, note that gdal_translate can do simple tone mapping
for you:
https://gdal.org/programs/gdal_translate.html#cmdoption-gdal_translate-scale

Patrick





On Wed, Mar 17, 2021 at 3:23 PM <Matt.Wilkie at yukon.ca> wrote:

> SPOT 6/7 satellite imagery is captured with a dynamic range of 12 bits per
> pixel per channel (ref <https://eos.com/spot-6-and-7/>). However almost
> all of the SPOT imagery I have seen in use has been 8 bits per channel, and
> split into RGB natural colour (Bands-321) and Near-infrared-RG false colour
> (Bands-432). What information is lost in this 12 to 8 bits conversion?
>
> I'm wondering if we should be altering our request for purchase
> specifications to deliver the full bit depth.
>
> *Although I'm referencing SPOT imagery specifically the question is
> general and really applies to any satellite or sensor system.*
>
> Cross-post:
> https://gis.stackexchange.com/questions/390315/what-is-lost-when-converting-12-bit-imagery-to-8-bit
>
>
>
>
>
> *Matt Wilkie*
>
> Geomatics Analyst
>
> Environment | Technology, Innovation and Mapping
>
> T 867-667-8133 | *Yukon.ca <http://yukon.ca/>*
>
> *Hours: 08:30-16:30, Tue-Wed: Office, Thu-Fri: Remote.*
>
>
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