How to calculate numers inside an array in python?

Question

I want to check some Numbers for a color recognition. I'm new to python so please do not judge me.

thresholdR = 50
thresholdG = 50
thresholdB = 50
middleValue = [225,165, 25]
    
lowerBound = [middleValue - thresholdR/2,middleValue - thresholdG/2,middleValue - thresholdB/2]
upperBound = [middleValue +  thresholdR/2,middleValue + thresholdG/2,greenMiddle + thresholdB/2]

When I try to run this I get the error:

TypeError: unsupported operand type(s) for -: 'list' and 'float'

I don't know how to fix this I would be so pleased if you could help me!

middleValue is a list. You can't subtract a value from it. Do you want to calculate those lower/upper bounds for every element of middleValue? — kuro
– kuro, Commented Apr 28, 2021 at 14:00
Did you mean: middleValue[0] - thresholdR/2 to mean red value - threshold/2? — quamrana
– quamrana, Commented Apr 28, 2021 at 14:01
@kuro yes thats right so I would have to use middleValue[0], middleValue[1] and middleValue[2] ? — Mr Spoony
– Mr Spoony, Commented Apr 28, 2021 at 14:01

Siddartha Reddy · Accepted Answer · 2021-04-28 14:21:48Z

1

You can not just substract a integer from a list. Maybe u mean this

lowerBound = [middleValue[1] - thresholdR/2,middleValue[2] - thresholdG/2,middleValue[3] - thresholdB/2]
upperBound = [middleValue[1] +  thresholdR/2,middleValue[2] + thresholdG/2,middleValue[3] + thresholdB/2]

answered Apr 28, 2021 at 14:21

Siddartha Reddy

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Smolakian · Accepted Answer · 2021-04-28 14:23:19Z

0

You need to add array indexers to your middleValue references.

lowerBound = [middleValue[0] - thresholdR/2,middleValue[1] - thresholdG/2,middleValue[2] - thresholdB/2]

edited Apr 28, 2021 at 14:23

answered Apr 28, 2021 at 14:03

Smolakian

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