topic Re: IMX6DL: How to do LCD calibration ? in i.MX Processors

IMX6DL: How to do LCD calibration ?

robinsingh — Fri, 26 Aug 2016 17:48:53 GMT

Hi All

The red colour on my LCD is little off, it does not exactly looks like perfect red. So i want to calibrate this LCD. And i am looking for the suggestion to do that:

here is gamma correction steps, i already tried and did not get the good result

Gamma correction on i.MX6

ipu-examples release notes - v0.1

ipu-examples/framebuffer_ex1.c at master · rogeriorps/ipu-examples · GitHub

Tried above gamma correction sample code but LCD calibration become more bad.

here is my platform and setting for LVDS interface :[ Android 4.4 kernel 3.10 ]

LCD panel uses (HX8282 -Source driver / HX8696 -Gate Driver) ---SPI interface is not out from the Panel for control so i can not set the panel registers.

====(drivers/video/mxc/mxc_lcdif.c)===================================

static struct fb_videomode lcdif_modedb[] = {

{
/* lcd 1024x600 @ 60 Hz , pixel clk @ 66MHz */
"HiMAX-WSVGA", 60, 1024, 600, 25000 , 155, 160, 8, 23, 4, 4,
FB_SYNC_CLK_LAT_FALL,
FB_VMODE_NONINTERLACED,
0,},

};

===( DTS file ) ===========:

mxcfb1: fb@0 {
compatible = "fsl,mxc_sdc_fb";
disp_dev = "ldb";
interface_pix_fmt = "RGB24";
default_bpp = <24>;/*<24>;*/
int_clk = <0>;
late_init = <0>;
status = "okay";
};

================================================================

Questions :

1) I used the ipu example code for gamma correction, where Gout array is :

int gout[16] = {0,2,4,8,16,32,64,96,128,160,192,224,255,255,255,255}; this setting do not have any impact on my LCD color, is there any other gout value for my processor imx6dl , which i need to use or How will i calculate these value , any suggestion ?

2) Reference manual section: 38.4.9.6 Gamma correction says" Required gamma correction slope for a specific panel/display should be provided by the display manufacturer " , can you point me, what will be the value i will be suing from gamma slope in the sample code ?

3) Regarding Data format, My LCD support RGB stripe(LCD document does not provide good details about this), And "RGB24" is working for me with reasonable result. Android HAL is using HAL_PIXEL_FORMAT_RGB_565 . is there anything i need to look from this perspective, In terms of IPU Color space conversion ?

4) Any other pointer or reference for LCD panel calibration ?

Thanks

Robin Singh

Re: IMX6DL: How to do LCD calibration ?

igorpadykov — Mon, 29 Aug 2016 00:02:43 GMT

Hi Robin

one can try to use yuv viewer tool to show the YcbCr & Y’Cb’Cr image to

get an intuitive color change perception. Gamma correction slope for a specific

panel/display should be provided by the display manufacturer, one can try to

change koefficients experimentally to see effect and imitate it on PC computer.

Also one can try hue control (implemented by mixing the Cb and Cr data)
using formula provided on

http://www.google.ch/patents/US20040021671
https://en.wikipedia.org/wiki/Hue

Best regards
igor
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Re: IMX6DL: How to do LCD calibration ?

vikaspatil — Thu, 29 Dec 2016 05:41:03 GMT

Hi Robin,

Looking for the same solution for custom target based on i.MX6Dualite. Have you achieved it? Could you share your finding and solutions if possible?

Thanks & Regards,

Vikash