Hi Pavel,
On 12/31/18 5:28 PM, Pavel Machek wrote:
Hi!
There is still HSV approach [0] in store. One problem with proposed
implementation is fixed algorithm of RGB <-> HSV color space conversion.
Maybe allowing for some board specific adjustments in DT would add
more flexibility.
[0] https://lkml.org/lkml/2017/8/31/255
Yes we could do HSV. Problem is that that we do not really have RGB
available. We do have integers for red, green and blue, but they do
not correspond to RGB colorspace.
OK, so conversion from HSV to RGB would only increase the aberration.
So, let's stick to RGB - we've got to have some stable ground and this
is something that the hardware at least pretends to be compliant
with.
I'm not saying that we should stick to RGB. I'm just saying that
problem is complex.
And no, hardware does not even pretend to be compliant with RGB color
model ( https://en.wikipedia.org/wiki/RGB_color_model ). In
particular, in RGB there is non-linear brightness curve.
Quotation from the wiki page you referred to:
"RGB is a device-dependent color model: different devices detect or
reproduce a given RGB value differently, since the color elements (such
as phosphors or dyes) and their response to the individual R, G, and B
levels vary from manufacturer to manufacturer, or even in the same
device over time. Thus an RGB value does not define the same color
across devices without some kind of color management"
This claim alone leaves much room for the manufacturers to pretend that
their devices are compliant with RGB model.
Much room, but everyone agrees that R=G=B=255 should be some kind of
white, and what other colors "approximately" mean.
I have two monitors, and no, colors don't match.
Do you have access to RGB led? Try to compare two monitors, and then
RGB led with monitor. RGB led will be _way_ off.
This chart makes sense:
https://www.rapidtables.com/web/color/RGB_Color.html
Try it on your LED device...
I believe problem to start with is the "white" problem. Setting
R=G=B=255 will _not_ result in anything close to white light on
hardware I have.
RGBW LED controllers solve this problem. For the devices without
white/amber we cannot do more than the hardware allows for.
But the hardware can do some kind of white. It is just that R=G=B=255
will result in green-ish-blue and something like R=255, G=50, B=10 is
neccessary to get approximation of white.
IMO good start would be to specify what kind of intensities are
neccessary to approximate white. And then try converting from RGB to
led intensities, and see if it somehow works.
I don't have access to RGB LED, and unfortunately have lack of time
currently to play with it even if I had one.
In order to gain a full understanding of your idea of RGB to LED
intensity conversion, we'd need to see the full algorithm.
It feels like imposing some restrictions on user regarding
the available scope of colors to set.
--
Best regards,
Jacek Anaszewski
