Colour Calibration Discussion

  • Hi everyone, we have a great tutorial for colour calibration but I somehow don't get it perfect. I thought it would be nice to have a thread to discuss and gather tips for reaching the perfect colours. So feel free to add your expertise below.


    Common issues I experienced so far:
    - green cast on yellow
    - dark grey reproduced as green
    - dark brown reproduced as red


    My understanding of the settings:


    Whitelevel: Maximum brightness of the colour
    Gamma: Brightness curve of the colour (outputColour = inputColour^Gamma)
    Pure colour settings: Additional colour mixed into pure colour in order to reproduce TV image
    Threshold: Data below set value will be lost
    Temperature: ? (Is there a difference to whitelevels?)
    Saturation: Amount of general colour (low settings will mix the other two colours into the output to reduce saturation, right?)
    Brightness/Luminance: Amount of white (increases or decreases the output values of all colours at the same time)


    Now to my problem:
    I used the wiki etc. but there is an issue that I can't fix and maybe it's my perfectionism :D
    I got my white levels fine. Green and especially Blue are way to bright so I reduce them significantly. White is alright then. I use the grey scale pictures to calibrate the gamma values. So I get a nice grey. Now comes the problem. If I am around a gamma of 2.5 or higher, dark colours are fine. Even a dark brown is somewhat possible. Problem is that midtones are way to saturated. If I reduce the saturation I lose most of the colour in bright colours and a decent amount in pure colours.
    So another option is to reduce gamma to around 2. That way midtones become brighter and therefore less saturated. But then dark colours become way to saturated and intense. For example a subtle dark brown becomes a very saturated red. Another effect is that the Leds light up on black which shouldn't happen. Of course a threshold solves this but then you lose colour nuances. (Example: threshold=0,2=51; 200/50/0 will be 200/0/0)


    I don't really know how to fix this. Also how does the temperature effect the colours? Whitelevel is the maximum brightness of the colour. But what does temperature do?


    Lets gather some input. I am sure some of you encountered this. Maybe we can also think of ways on how to improve the colour processing algorithms. I think that the more people understand how hyperion processes the colour, the more ideas will come on how to improve it. One way that was discussed is to reduce saturation for dark colours. But maybe you have got more ideas.


    Cheers.
    doc.ex

  • Great idea, yeah this forums needs anyway more topics with overall conversations about all topics to share experience and ideas :)
    The biggest problem of Hyperion i think are the led chipset variety. If i see for example that bad white values for ws2801- crazy. There is not much space to create colors.
    But i have to admit i still fight with the new calibration even with my APAs, My old configuration had very very good color adjustment. nearly everthing perfect! Desert, yellow, brown, cyan and grey levels. Very amazing. I need to create a video of this to show you.



    Maybe
    @AEtHeLsYn want so say something to this ;)


  • The biggest problem of Hyperion i think are the led chipset variety. If i see for example that bad white values for ws2801- crazy. There is not much space to create colors.
    But i have to admit i still fight with the new calibration even with my APAs, My old configuration had very very good color adjustment. nearly everthing perfect! Desert, yellow, brown, cyan and grey levels. Very amazing. I need to create a video of this to show you.


    Yeah, for my lpd8806 I need to reduce the white levels to about 255/140/100. Thats pretty bad as well. But I guess thats the price when you buy cheap chinese stuff without a proper quality assurance. I have the feeling that my old calibration was working better as well. The pure colours weren't as good since I didnt't have the option to correct them but, apart from that everything was fine. But the same settings don't work anymore. Because of the lower gamma values the leds turn on on black. Threshold is something I try to avoid for above mentioned reasons

  • Try some "extreme" settings. And use the whitelevel values to dimm down your leds (even though wiki told us not to do so :P )
    I get some pretty nice brown tones this way, without ruining other colors or brightness situations.



    However, with these low values, hyperion seems to become a little bitchy :D Weird "pop up / jumpy" effects here and there and sometimes totally wrong colors. When i move a window there and move it back color is fine again.

  • @HalbesHaehnchen I tried your method. I did achieve some great brown tones, but because of the low whitelevel values, a lot of dynamic range is lost. However your method kinda works with the backlight option since you don't need a lot of dynamic range. I however prefer the leds off on black so I kept to my old settings and tweaked them until I got satisfied. I attached my config for everyone interested. Dark tones are still a little oversaturated and bright areas lack saturation but the midtones are perfect. :)


  • Keep in mind that those settings are specific to my combination of strip and tv, so you probably have to adjust them quite a bit. However the best midtone colours I could reach required the gamma values in the 2.3 to 2.5 region. So maybe that is of help to you.

  • Well I think the leds are just poorly optimised for human perception. Human eyes are more sensitive to certain colours. For example, we are much more sensitive to green than to red and blue. In other words, when the leds emit the same brightness for all colours, we we would perceive the colour as warm green. I guess my strip is just really bright for blue and not bright enough for red, which is why I have to adjust a lot. That also takes away a lot of dynamic range within the colour channels. I will buy new leds in the future. I am just not sure yet which ones. Maybe RGBW and I also wanna try a different layout. More like an oval shape instead of rectangular, to get a nice halo and improve the diagonal glow.

  • some info about temperature:
    this is not implemented, this is just the old "correction"
    "temperature" makes a linear mapping between input values 0-255 to output values 0-limit


    limit is the thing you can configure in config (red green blue).


    temperature values 255 255 255 in above example makes nothing. This maps input values 0-255 to output values 0-255 (per channel).


    I suggest: delete temperature block from config and save performance and memory, because it is useless and somhow the adjustment code contains same feature

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