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Does LightCrafter Color presents colors on HDMI mode RGB video streaming independently??

Mohammad Hossein Khani
Prodigy 50 points

Hi,

I work on color vision and I want to use lightcrafter EVM to for color presentation. For me it is important that I can drive each LED independently through HDMI port with Opengl program.

I wanted to measure the spectrum of LEDs with spectrometer (Thorlabs) and I noticed that when I increase the intensity of one LED like blue, I see an increase in intensity of another LED like green.  It seems that some color correction or color modification gets place in the FPGA of the lightcrafter.
 So my question is, doese lightcrafter displays colors independent of each other when it is on HDMI streaming mode or not?

if FPGA enhance or modify the RGB presentation, is there a way to disable this feature? (I look into the ti programmers guide, but I couldn't find out where to modify the hex values)

I use lightcrafter control software version 5.0.0 (latest version on ti webpage)

Thanks in advance.

Best.

  • 0
    TI__Genius 11355 points

    Hi Mohammad,

    Thanks for posting. Can you provide some more detail on your use case and how you are testing? What are your HDMI Port Display Mode Settings and LED current values? What are you adjusting them to? Any other steps you are performing in your tests?

    Thanks,

    Clinton

  • 0 in reply to Clinton Rodgers
    Prodigy 50 points

    Hi Clinton,

    Thanks for your response,

    In principle I investigate the mechanisms of color processing in the mouse retina. I present visual stimuli from a RGB projector (in this case Lightcrafter evm) and record the activity of mouse retina and based on this I am interested to know how chromatic stimuli is processed in the eye.

    Since neurons are inherently nonlinear for me it is really important that my stimulus presentation of each color is linear, stable, fast and at the same time independent of other colors. To achieve these I do gamma correction. I use a photodiode (PDA-750 Terahertz Technologies) and measure all the possible intensities that my graphic card can generate (8 bit GPU, 256 intensity steps generated by custom made OpenGL program) and then using a transfer function, I make each LED's presentation linear. Furthermore I measure the spectrum of each LED (Thorlabs ccs200 spectrometer) to calculate isomerization rate of each cone in mouse retina.

    Before I go through details of measurement, it is important to say since mouse retina is only dichromatic and has UV and green cones, I had to modify the light engine of lightcrafter to have effective stimuli presentation. I therefore replaced the blue LED of the lightcrafter with UV LED (nichia NCSU276A- (U365)) and made a new lens system with all new UV fusing lenses.

    First time when I measured the spectrum I found strange fluctuations in the intensity of each LEDs. For that measurement I used RGB video streaming with 864x480 resolution at 60 Hz.

    Now I did intensity measurement using photodiode, so I measured all the intensity values of 1) UV, 2)Green, 3) Red, 4) Green+Red (Yellow), 5) UV + Green (Cyan), 6) UV + Red (Purple), 7) UV + Green + Red   (White). I did these measurements in 864x480 resolution and also 608x684 and I attached the curve I got from these measurements. 

    As you can see for all the LEDS these are fluctuations at different intensity values. I guess this has been reported before in this post


    Two more things, first for my measurements I used value of 1 for all LEDs at lightcrafter gui. The reason for that is lightcrafter is too bright for retina and it bleaches the retina so I want it to be as dim as possible that why I prefer to use it with LED values at 1. I did however some measurement with LED values at 274 and saw same fluctuation in LEDs curve. In case of UV LED the fluctuation were so much my photo-diode could not read stable values at all.

    Second my uv LED is not as bright as OSARAM green and red LEDs therefore in measurement with two colors (cyan, purple) and white we cannot see the effect of uv LED clearly. However when I measured the uv only with more precision (nA instead of microA) I saw same fluctuations.

    so now my questions:

    first what is the source of these fluctuations, does it depend on the HDMI video streaming mode or the resolution of the lightcrafter? is there a way to solve this problem?

    Second could replacing blue LED with uv have some influence on these fluctuations, if yes then why I get them with green and red LEDs too. I checked the connection of uv LED with its LED base and there is no problem with LED connection. I checked the forum and there are others who did the same uv replacement, I guess there is even a commercial version of lightcrafter with uv too, so do you know if they report same problem or not?

    last, my question is about the independence of the RGB LEDs in lightcrafter. At least from my measurement it seems that each LED works independent of others. It seems that there is no color correction circuit that interfere with presentation of each color or no optimization one color to another one or similar things that I saw in some commercial projectors.

    Sorry for the very long question, and thanks a lot for reading and answering them in advance.

    Calibration_Plots_All at LED value 1_with640x608.rarCalibration_Plots_Allat LED value 1_with864x480.rar