When I click on "information" of a Landsat 8 image (bands 1,2,3,4,5,6 and 7 are combined), I get three RGB values: 10928, 10137 and 10265 respectively.
What do these values mean?
They don't correspond to the usual 0-255 RGB values.
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It is because the Landsat 8 images are provided in 16 bit instead of 8 bit in previous Landsat images. It is stated clearly in USGS-Landsat-8:
These sensors both provide improved signal-to-noise (SNR) radiometric performance quantized over a 12-bit dynamic range. (This translates into 4096 potential grey levels in an image compared with only 256 grey levels in previous 8-bit instruments.) Improved signal to noise performance enable better characterization of land cover state and condition. Products are delivered as 16-bit images (scaled to 55,000 grey levels).
Here is another information using How does Landsat 8's 12-bit data improve data products?, and the answer is:
Landsat 8’s Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS) sensors provide improved signal-to-noise (SNR) radiometric performance quantized over a 12-bit dynamic range.
This translates into 4096 potential grey levels, compared with only 256 grey levels in previous 8-bit instruments. Improved signal to noise performance enables improved characterization of land cover state and condition.
The 12-bit data are scaled to 16-bit integers and delivered in the Level-1 data products. Products are scaled to 55,000 grey levels, and can be rescaled to the Top of Atmosphere (TOA) reflectance and/or radiance using radiometric rescaling coefficients provided in the product metadata file (MTL file).