Ivo is there a link to the correct colour palette for HST , HOO SOO images . and what does HOO and SOO stand for obviously HST I know Hubble Space Telescope , so many you tubers kicking out images just wanted to get to the bottom of what the correct colouring should be ie scientific as opposed to artistic licence .
Regards Dave
Hst and Hoo , Sho colour references
Re: Hst and Hoo , Sho colour references
It's a bit more subtle than that.
There is no prescribed mapping of the narrowband filters to a specific hue. Anything goes.
The point of the color mapping, is to make different emission concentrations visible. E.g. by looking at the hue of an area, you should be able to tell what emissions are dominant.
With the above goal in mind, although you can pick any color you like for the various bands, people tend to pick colors that are complementary in the RYB or RGB color wheel (say blue and orange/yellow, cyan and red, etc.). This maximises a human's ability to discern between regions of different emissions.
Where things go wrong, is usually when people make mistakes in processing that cause hue shifts and makes it impossible to compare areas of different emissions in the image.
To demonstrate one such common mistake using simple color chart(source Fernandes, João Carlos & Campos Neves, Jose & Sepúlveda, Manuel & Afonso, J.L.. (2008). Simple camera calibration for light measurements. IEEE International Symposium on Industrial Electronics. 1025-1028. 10.1109/ISIE.2008.4677211. );
Now watch what happens when the the blue channel alone is non-linearly stretched extremely hard in GIMP;
Versus what happens in StarTools (which linearly throttles channels);
We just massively increased the blue channel, skewing any blue "emission" to maximum. In other words, the blue channel should really be "useless" and any colors we should be seeing should be solely the result of variations in the green and/or red channels. Blue is sticking at 100% blue for the purpose of hues.
In other words we should be seeing hues between cyan and purple and nothing else.
Take the yellow square for example. A yellow square is made up of max red, max green and very little blue. Therefore, maxing out the blue as well should yield white (max red, max green, max blue). This happens correctly in the ST image.
In the image with the blue channel individually stretched vs the others, we can see hues that vary all over the place, not to mention brightness differences. Now thinking back to the purpose of channel mapping. Suppose we mapped S-II to red, Ha to Green and O-III to blue (the famous Hubble palette, aka SHO or RGB:SHO palette). In the ST image we maxed O-III, causing every square to exhibit lots of O-III equally.
The other images, however, erroneously suggests that some areas have more O-III than others. For example, the background now has been given lots of O-III versus brighter squares. This would not be accurately reflecting reality.
Hope this helps!
There is no prescribed mapping of the narrowband filters to a specific hue. Anything goes.
The point of the color mapping, is to make different emission concentrations visible. E.g. by looking at the hue of an area, you should be able to tell what emissions are dominant.
With the above goal in mind, although you can pick any color you like for the various bands, people tend to pick colors that are complementary in the RYB or RGB color wheel (say blue and orange/yellow, cyan and red, etc.). This maximises a human's ability to discern between regions of different emissions.
Where things go wrong, is usually when people make mistakes in processing that cause hue shifts and makes it impossible to compare areas of different emissions in the image.
To demonstrate one such common mistake using simple color chart(source Fernandes, João Carlos & Campos Neves, Jose & Sepúlveda, Manuel & Afonso, J.L.. (2008). Simple camera calibration for light measurements. IEEE International Symposium on Industrial Electronics. 1025-1028. 10.1109/ISIE.2008.4677211. );
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- Reflective-color-chart-reference.png (59.03 KiB) Viewed 1871 times
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- Untitledheavystretch.png (52 KiB) Viewed 1871 times
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- Reflective-color-chart-reference_ST.png (54.06 KiB) Viewed 1871 times
In other words we should be seeing hues between cyan and purple and nothing else.
Take the yellow square for example. A yellow square is made up of max red, max green and very little blue. Therefore, maxing out the blue as well should yield white (max red, max green, max blue). This happens correctly in the ST image.
In the image with the blue channel individually stretched vs the others, we can see hues that vary all over the place, not to mention brightness differences. Now thinking back to the purpose of channel mapping. Suppose we mapped S-II to red, Ha to Green and O-III to blue (the famous Hubble palette, aka SHO or RGB:SHO palette). In the ST image we maxed O-III, causing every square to exhibit lots of O-III equally.
The other images, however, erroneously suggests that some areas have more O-III than others. For example, the background now has been given lots of O-III versus brighter squares. This would not be accurately reflecting reality.
Hope this helps!
Ivo Jager
StarTools creator and astronomy enthusiast
StarTools creator and astronomy enthusiast
Re: Hst and Hoo , Sho colour references
Thanks for the explanation Ivo 