Color scale in "Sentinel Hub Playground" images


#1

Hello everybody

I’m currently using “Sentinel Hub Playground” (I plan also to move to the EO-browser soon, although I have still some problems with this - depending probably on my PC browser).

Now, what is a bit problematic with Playground, is that most of the available renderings (like “Color Infrared”, “Vegetation index” or “Moisture index”) cannot be easily understood because of the absence of a colorbar showing the color scale and the corresponding values.
For example, what is color associated to the highest moisture index, dark blue or light blue or something else? This is not easy to figure out since no information is given on that.
Apart from “Natural color” rendering, obviously , all the others renderings suffer more or less from this issue.

Another point (maybe trivial for you) but that it is not entirely clear to me is the the following: is the color scale always the same (for example: does the same color correspond to the same Moisture index value, in all the the maps, at any time and in any place, or there is some kind of normalisation in every map/tile, so that the same color corresponds to a value depending on the map?)
This should be clear if you could provide some color bar associated to the map, by the way.

So, is it possible to show the color scale (with the corresponding numerical values) on the Playground rendering itself? Or, if it is not, where can I find at least a reference color scale?
Is this problem bypassed or fixed by using your “EO-browser”?

Thank you in advance and best regards!


#2

Hello Nicola,

Playground currently doesn’t support legends and we are unable to promise if and when they will be added. That said, EO Browser does support them, and it should be very similar to Playground in its core functionality (it has many other features, but you can ignore those until you need them).

Could you share the problems you are having with EO Browser so we can advise on how to solve them?

Kind regards,

Anze @ Sinergise


#3

Dear Anze
many thanks first.

“Playground currently doesn’t support legends”-> ok, I understand…
What can you tell me about my second question, please, i.e wheter the colors in all the maps are univocal, regardless of the time and of the place (so that different Playground images can be straightforwardly “compared”)?
Sorry if it is a silly question or if even it doesn’t make any sense, I don’t know how you create these images, so in principle I cannot know how it works.

“Could you share the problems you are having with EO Browser” -> I’m using Safari 9.1.1 on MacOSX10.11, so I’m not realli up-to date, it’s probably my fault on this… I’ll try to download some newer browser, like Opera or Chrome (do you have any other suggestion?).
Anyway, what I do now is just to go to:


then I leave the dafault values (even with the map centered around Rome), I click on “Search” button and everything disappears!!!
I have the last version of java installed and everything enabled, so I think it is just an issue of Safari…

Best regards
Nicola


#4

Let me try to answer some of your questions:
Satellite imagery is a bit tricky - the sensors on the satellite are generally calibrated pretty well, so the same “situation” should result in the same value (reflectance). However, there is atmosphere in a way and this is changing - clouds, fog, thickness of the atmosphere, angle of the sun, etc. All of these affect the values. The atmospherically corrected data should improve this to some extent, so I recommend you use “L2A” type of the data (there is an option for this in EO Browser). However, this is still approximation so some changes remain.

I recommend using Chrome, it will probably work best.


#5

Hi Grega.
Thank you for your comments about the calibrations and for your suggestion concerning the browser.
Chrome works really well together with EO Browser, I have just started practising with the different options and with the available representations and so on…
Now I’m back to my first question - how can I get a colorbar or any useful information about the color scale for all-except-for-the-true-color images?


#6

You will find the legend by expanding the layer name, see the image below.
Legend is only available where we found reasonable information behind, e.g. NDVI, scene classification (with L2A), Sentinel-5P values, etc. Many EO products are not that straightforward to “interpret”. You will probably have to study the details of each of these indices.

I suggest checking:


https://www.indexdatabase.de/

Once you get familiar with the data and indices, you can create your own layers and define the legend however it fits you:
https://www.sentinel-hub.com/faq/how-define-custom-legend