Computing L1C TCI from RGB Bands

Optical Toolbox
1

Hello,

I am trying to reproduce the TCI RGB 8bits image from the B04, B03 and B02 bands of an image and failing to reproduce the exact results,

Currently I tried the following (from the 16bits band data)

  • Clip to and normalize each band by 4095 then stretch to [0,255]*
  • Normalize each band by the maximum per band, then stretch to [0,255]**
  • Clip to and Normalize each band in the [1th percentile / 99th percentile] of each band,then stretch to [0,255]***
  • Normalize by 10000, clip to 0.2 then stretch to 0-255 as per User Guides - Sentinel-2 MSI - Definitions - Sentinel Online - Sentinel Online

In numpy, providing x is the RGB in int16 obtained from [B04, B03, B02] converted to float32:

*: x = np.clip(x / 4095., 0., 1.) * 255. (then to np.uint8)
** x = x / np.maximum(x, axis=(0,1))
*** x = (x - np.percentile(x, 1) ) / (np.percentile(x, 99) - np.percentile(x,1)) . clip(0.,1.) )

Is there an official public algorithm to convert [B04, B03, B02] to the TCI jp2 ?

For reference, thereā€™s also a ā€œcustom scriptā€ on sentinel hub to get TCI (custom-scripts/sentinel-2/true_color/script.js at main Ā· sentinel-hub/custom-scripts Ā· GitHub) but I donā€™t know the starting spaceā€¦

Best regards,

2

Hii,

In sentinel - 2A assets there is ā€˜visualā€™ property which returns rgb image of 8-bits, but I am unable to reproduce the same with with 16-bit values from (B2, B3, B4) bands through any kind of normalization.
I am currently searching all over the internet, for such public algorithm to convert 16 bit sentinel-2A images to 8-bit images.

Am wondering if you found any?

3

The EO Browser says it uses a gain of 2.5 for each of the three bands.

4

Hi can someone from the sen2cor team answer this? I canā€™t find the exact equation for computing TCI from the RGB assets anywhere for either L2A or L1C

5

@Sen2cor_dev_team

6

I found this post: What is the algorithm used to normalize 16-bit valued sentinel-2A bands to 8-bit valued bands? - #7 by TomAugspurger

but the primary answer only references internal Java code that is difficult to follow. Would be great to have the exact equation in the docs in pseudocode.

1 Like
7

Dear @rbavery,

In Sen2Cor v2.11 a saturation at 25% of surface reflectance is used to generate the L2A TCI.

Meaning that a pixel with a surface reflectance of 25% (or higher) will be set at 255 in the 8bits image.

Please note that the official L2A TCI generated by ESA uses a software component external to Sen2Cor. It is the same software component used to generate the L1C TCI, with different configuration parameters.

A previous answer is available here: What is the valid range for the TCI product? - #2 by TomAugspurger

We may add this information to the Sen2Cor Frequently Asked Questions.

Cheers,
@Sen2cor_dev_team