Hi Seyedeh,
If your LED light sources are of the RGB type, then you should not rely on a
digital camera to determine the correlated color temperature. The reason is
that the RGB spectra are fairly saturated, and most cameras do not measure
saturated colors accurately.
If your LED light source uses white LEDs, then you *might* get a reasonable CCT
result if you convert the images using the dcraw freeware tool to a linear
output format such as 16-bit TIFF. For example, I would use:
dcraw -w -4 -t 0 -T input.raw
The dcraw program has a much better notion of the correct color space for most
cameras than Photoshop or the camera itself. Since Photosphere and hdrgen take
the JPEG from the camera, their color results are not as reliable. Also, you
don't need HDR to measure a light source, as you don't care about light/dark
detail. You just have to make sure your exposure is not clipped.
Cheers,
-Greg
> From: "Mahlab, Seyedeh Farzaneh" <[email protected]>
> Date: February 6, 2017 1:53:22 PM PST
>
> Hi every one
> I am taking HDR images of different white LED light sources with different
> color temperature emitting on white diffusive background. I am trying to
> calculate CCT of each light source based on RGB extracted. But I am not sure
> how wide an HDR image can cover the differences between white color, like
> cool white and warm, based on RGB. I also illustrate them on chart to see how
> RGB values are acting for different light sources. As shown in the following:
>
> So my question is : 1)is HDR able to give me the difference between white
> colors (different CCT) based on RGB value ?( or would I be able to extract
> CCT from an HDR image ?)
> 2) when the light source is getting cooler, R values getting slightly lower.
> Is this point of view acceptable here ? B and G value are almost the same. Is
> there a reason for that ?
> Thank you very much !
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