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Lightcrafter 4500 greyscale linearity

boblee
Prodigy 90 points

I am displaying a horizontal ramp image and the intensity profile is not linear.  There is a large discontinuity at code 112 when using HDMI input in video mode.  The ramp is linear below this code but has banding throughout the ramp above 112. 

Using the LED intensity controls to look at the colors one by one it is clearly the blue channel at fault.  Red and green are linear. 

Staying in video mode and switching the "source" to "internal test pattern" gives the same result (banding) and again only on the blue channel.

How to fix?

  • 0
    TI__Mastermind 30875 points

    Hello Boblee,

    Video Mode is not a desired use model for greyscale linearity measurements. Note in the video mode the % of frame time allocated b/w Red and Green and Blue is not even, Red - 35%, G - 45%, and Blue - 20%. So in 20% time not all 8-bits  of greyscale are shown. Finally Video Mode is for intended for general human viewing not for machine level measurements.

    So, please perform the tests, by configuring it in Pattern Mode with source as external RGB port.

    Regards,

    Sanjeev

  • 0 in reply to Sanjeev
    Prodigy 90 points

    Hi Sanjeev,

    I do have here a human viewable application and need to use the video mode with HDMI.  I have not "measured" anything- the problem is evident by straight visual inspection.  I found the code value where the discontinuity exists by using a photo editor program to query pixel values on my PC desktop screen.

    The picture below shows the problem.  This image results from these settings: Video Mode + Internal Test Pattern + RGB Ramp.  The discontinuity in the blue ramp is undesirable by itself, but it also causes the white point to shift on the grey ramp.

    The red and green ramps are smooth.  How can the blue ramp be made smooth?

  • 0 in reply to boblee
    TI__Mastermind 30875 points

    Hello Boblee,

    Thanks for providing the picture.

    We want to let you know that the Smooth Ramp + White Point => requires retuning the [Video Sequences] . I am afraid this is something not available in the Advanced Light Control chipsets. The LightCrafter4500 is geared more toward industrial application or non-human inspection systems than basic video projection system. Look at the following chipsets from TI http://www.ti.com/lsds/ti/dlp/video-and-data-display/getting-started.page they are like regular display projectors.

    Let us know if it helps.

    Regards,

    Sanjeev