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How is luminance calculated?

Hi,

I'm using the Color Plane Extraction function on Vision Assistant to extract an the luminance plane of an image, but was wondering how exactly the luminance is calculated? Also, what is the difference between luminance and intensity?


Thanks!

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http://en.wikipedia.org/wiki/Luminance

 

While luminance is rather clearly defined, intensity isn't. It could be synonimous to luminance intensity but it can also mean a number of other things.

Rolf Kalbermatter
My Blog
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Hi Rolf,

 

I know you posted almost year ago, but I currently also run into similar problem. 

 

You are pointing to the wiki where luminance is defined in terms of luminous flux.

I think in regards to the LV calculations the question is how it is obtained from RGB values, then the closest answer is here (referred to as relative luminance):

 

http://en.wikipedia.org/wiki/Luminance_(relative)

 

What is puzzling is that according to this formula you can easliy use all 24bits of color information to get luminance, yet LabView is only yielding 8bit plane for luminance?

 

Does anyone know how LV is calculating that?

 

Mike

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Hi bignicewolf,

 

Here are some resources for how RGB and HSL images are represented. Luminance is just a component of HSL. For a 32-bit RGB image converted to a 32-bit HSL image, the luminance component would be 8 bits.

 

Image TypesMeasure Color Statistics

 

David B.
Applications Engineer
National Instruments
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Hi dshusker,

 

Thank you for the answer, knowing the inner image representation helps to understand why you have 8bits for Luminance plane. 

 

To be diligent on this thread can you answer how the luminance is internally calculated ? (from 24bits of RGB -> 8 bits of Luminance in HSL format)

 

I'm wroking in spectral imaging field and each color chanel carries diffrent portion of the information, yet some analysis is best done in HSL domain so knowing exaclty how you go from RGB to HSL would be very helpfull.

 

Regards,

 

Mike

 

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I'm not sure how the calculation is done off the top of my head, but you may try looking at the Vision Concepts Manual for this.

Applications Engineer
National Instruments
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I just tested this and luminance in LabVIEW is calculated as:

 

L = 0.299*R + 0.587*G + 0.114*B

 

See http://en.wikipedia.org/wiki/Luma_%28video%29 for more info about luminance (or luma).

 

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could you pls send me the VI which can meaure the y luma, u chroma component of the color image

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could you pls send me the VI which can meaure the y luma, u chroma component of the color image

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Hi Chris,

 

welcome to the forum!

 

Why do you need to post your question twice?

 

And what have you tried so far to create a VI from the (simple) equation given some years before?

Best regards,
GerdW


using LV2016/2019/2021 on Win10/11+cRIO, TestStand2016/2019
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