From: luweitest@gmail.com   
      
   On 2024-12-11 7:34, Michael Uplawski wrote:   
   > Supersedes for typo, Kraut2English in progress   
   >   
   > Good afternoon.   
   >   
   > My question first: Is it possible to measure the wavelength of the   
   > light emitted or reflected from a surface in a way that would be   
   > practicable for just anybody, and with objects that would have to be   
   > “tested” all few minutes?   
   > ...   
   Yes, like bob posted, what you need is a spectrometer designed for   
   surface reflectance measurement (380~780nm). I am not familiar with the   
   products in the market, yet I think it could use an integration sphere   
   with an opening size to cover a meaningful area, but not too big to   
   deviate much from the measurement principle, maybe 5~10mm diameter, and   
   with a space that could hold an apple under the opening.   
      
   Then you need the software to calculate the colour of the surface.Some   
   device may have the feature, or you can DIY (in principle, by multiply   
   the incident spectrum (sun's spectrum AM1.5 could be a reference), the   
   measured reflectance spectrum, and the 3 response curve of the human   
   eye,and integrate across 380~780nm). You will get a color coordinate,   
   which are 3 quantitative value that can be used to compare, reproduce,   
   or automatic select by machine.   
      
   It should be noted that the result is the colour and brightness   
   perceived by a "standard" observer (the integration sphere), not the   
   same as human eyes perceived in normal conditions. So you should not   
   select an area of the "preferred" colour (in this case green) directly   
   from the colour space (as in   
   https://en.wikipedia.org/wiki/File:CIE1931xy_CIERGB.svg), instead, like   
   in machine learning, you should use the "preferred" apples as samples to   
   get a "preferred" colour space area, then use it as the selection standard.   
      
   --   
   Wei Lu   
   PGP:	0xA12FEF7592CCE1EA   
      
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    * Origin: you cannot sedate... all the things you hate (1:229/2)