i.MX ProcessorsのトピックRe: imx6 android - dithering 24bit graphics on 18bit panel

imx6 android - dithering 24bit graphics on 18bit panel

mrabe — Tue, 17 May 2016 11:50:20 GMT

Hi,

We have a few problems with dithering in Android.

In our test arrangement, we've connected a 18bit panel via LVDS to an i.mx6 Quad.

Running Android 5.0 on it, a gradient test image shows a lot of chunks (as limited by the 18bit panel) - So It seems like dithering is not working. - But if we enable "Disable HW-Overlay" in the developer settings, everything get's dithered correctly.

Has anyone experienced similar problems, and/or got any idea on how to fix this problem?

Thanks in advance.

Re: imx6 android - dithering 24bit graphics on 18bit panel

SergioSolis — Tue, 24 May 2016 17:37:34 GMT

Hello Matthias,

I am unable to reproduce the problem since I don't have an 18bit panel, but can you please send me a photo of how it looks?, with and wihtout hardware overlays... if you disable to overlays, does it look good on any circumstance? (photos, videos, general UI, etc).

I would appear that the problem is the pixel clock and you would need to modify the settings to match with the 18bit panel.

Re: imx6 android - dithering 24bit graphics on 18bit panel

mrabe — Wed, 25 May 2016 16:36:29 GMT

Hi,

Thanks for the support.

The overall looks are improved by disabling hw overlays. - But our customer noticed that there is a problem with certain types of fonts. However I haven't been able to reproduce this for myself by now.

Here are the pictures you asked for.

"normal operation" with Display configured as RGB666 on an 16Bit Framebuffer.

Here with disabled hw overlay:

Any ideas what might be off?

Re: imx6 android - dithering 24bit graphics on 18bit panel

gary_bisson — Fri, 10 Jun 2016 09:10:56 GMT

Hi,

This is the same issue as this one:

Android ICS -> Lollipop upgrade on IMx6 creates image binding

Have you tried setting the bpp to 32-bit? Are you sure your LVDS display framebuffer is actually 24-bit (check the sysfs entries)?

Otherwise the difference with or without the HW overlays is the use of the GPU2D, when HW overlays are disabled everything goes through GPU3D instead of GPU2D.

Regards,

Gary

Re: imx6 android - dithering 24bit graphics on 18bit panel

gary_bisson — Mon, 13 Jun 2016 09:26:18 GMT

Hi SergioSolis,

Do you have a Hannstar 10" display (the one present on the Sabre SD Platform)? This latter is 18-bit LVDS display and the issue can be reproduced with it.

linux-2.6-imx.git - Freescale i.MX Linux Tree

Also I suggest downloading DisplayTester app and use the gradient test to see the issue.

As a FYI, once the bpp is set to 32, I couldn't reproduce the issue on HDMI display but it is still present on LVDS.

Please advise.

Regards,

Gary

Re: imx6 android - dithering 24bit graphics on 18bit panel

mrabe — Mon, 13 Jun 2016 12:03:28 GMT

Hi,

thanks for the response.

Yes, we've tried setting the default_bpp to 32 and it's a little bit better (since now, we can use the full RGB666 not only RGB565).

But it's still not great.

Our devicetree setting look like this - Can you see anything wrong with that?

/ {
        mxcfb1: fb@0 {
                disp_dev = "ldb";
                interface_pix_fmt = "RGB666";
                default_bpp = <32>;
                int_clk = <0>;
                late_init = <0>;
                status = "okay";
        };
};

&ldb {
        status = "okay";

        lvds-channel@0 {
                fsl,data-mapping = "spwg";
                fsl,data-width = <18>;
                crtc = "ipu2-di0";
                primary;
                status = "okay";

                display-timings {
                        /* ... */
                };
        };
};

Thanks again,

- Matthias Rabe

Re: imx6 android - dithering 24bit graphics on 18bit panel

SergioSolis — Tue, 14 Jun 2016 16:35:39 GMT

Hello Matthias,

It appears that the "chunks" are not identical between R G and B. R and B look to be the same and G is a bit more granular. Because of this, an immediate thought is that there is a mismatch in the RGB config somewhere, most likely the FB or the overlay. Something is likely configured for 565 rather than 666, can you check this?

Re: imx6 android - dithering 24bit graphics on 18bit panel

mrabe — Wed, 15 Jun 2016 10:33:17 GMT

Hi Sergio,

thanks for the response.

You are correct - Since RGB666 needs 2bit more, than a 16bit Framebuffer can offer, everything falls back to RGB565. But a 16Bit FB get dithered correctly if HW Overlay is disabled. That's why I took those example images for you.

A 24Bit/32Bit Framebuffer, that fits RGB666 doesn't get dithered, neither HW Overlay is enabled nor disabled.

I attached a picture for you, that shows RGB666 with 32Bit Framebuffer (sorry for the image quality, but you can still see the chunks),

Re: imx6 android - dithering 24bit graphics on 18bit panel

SergioSolis — Wed, 22 Jun 2016 18:55:44 GMT

Hello Matthias,

Was the change made in the Device Tree file to change the display from RGB666 to RGB565?

Re: imx6 android - dithering 24bit graphics on 18bit panel

mrabe — Fri, 24 Jun 2016 10:26:49 GMT

Hello Sergio,

yes, we tried this before, but there seems to be no difference between RGB666 an RGB565 with a 16Bit framebuffer.

Although RGB666 with 32Bit is a little bit better (as mentioned above).

Re: imx6 android - dithering 24bit graphics on 18bit panel

rogerio_silva — Fri, 24 Jun 2016 13:39:40 GMT

Hi,

I reproduce the problem on i.MX6Qsabresd + android and also on i.MX6Q Auto + Linux from NXP Yocto BSP.

Sending the gradient image to the both layers, background (/dev/fb0) and foreround (/dev/fb1), the image is correctly displayed.

When using a video player to display the png, the image is degraded as shown by the pictures sent by Matthias.

I'm supposing that the problem happens when the picture is displayed using v4l2 output (/dev/video17) and the color format set on v4l2 may be wrong.

I`ll make some tests and post the results here.

Re: imx6 android - dithering 24bit graphics on 18bit panel

rogerio_silva — Fri, 01 Jul 2016 13:20:47 GMT

The issue was escalated to Android R&D team and the solution is not complete yet.

Re: imx6 android - dithering 24bit graphics on 18bit panel

gary_bisson — Fri, 01 Jul 2016 13:28:55 GMT

Hi,

Well some customers already received updated hwcomposer libraries from NXP with the fix:

Android ICS -> Lollipop upgrade on IMx6 creates image binding

Regards,

Gary

Re: imx6 android - dithering 24bit graphics on 18bit panel

rogerio_silva — Fri, 01 Jul 2016 13:53:09 GMT

Hi Gary,

After that message, customer noticed some issues on image quality. This was reported on our internal ticket.

Would you like to test this preliminary composer library?

Best regards,

Rogerio

Re: imx6 android - dithering 24bit graphics on 18bit panel

gary_bisson — Fri, 01 Jul 2016 15:26:02 GMT

Hi Rogerio,

Sure, if you have Marshmallow libraries I'd be happy to try them out.

Regards,

Gary

Re: imx6 android - dithering 24bit graphics on 18bit panel

rogerio_silva — Mon, 04 Jul 2016 14:01:53 GMT

Hi Gary,

See attached hwcomposer_fsl.imx6.so file that fixes the issue, please replace device/fsl-proprietary/fsl-hwc/hwcomposer_fsl.imx6.so with attached binary.

Please, let me know about your tests and results.

Best regards,

Rogerio

Re: imx6 android - dithering 24bit graphics on 18bit panel

gary_bisson — Mon, 04 Jul 2016 18:17:24 GMT

Hi Rogerio,

I've tested it on Nitrogen6x + Hannstar display.

It works fine with a 16bpp framebuffer but the problem still exists with a 32bpp framebuffer.

Regards,

Gary

Re: imx6 android - dithering 24bit graphics on 18bit panel

rogerio_silva — Tue, 05 Jul 2016 16:52:49 GMT

Hi Gary, did you also tested on HDMI 32bpp? Is it ok on HDMI?

Re: imx6 android - dithering 24bit graphics on 18bit panel

gary_bisson — Tue, 05 Jul 2016 16:54:43 GMT

No, as I said I only tested LVDS, since not every case is working I didn't even try HDMI.

Gary

Re: imx6 android - dithering 24bit graphics on 18bit panel

rogerio_silva — Tue, 05 Jul 2016 18:13:31 GMT

I understand. I'll check it.