Author Topic: NHD-2.7-12864UCY3 Uneven brightness depending on neighboring pixels  (Read 1043 times)

mikaeleiman

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I'm testing the NHD-2.7-12864UCY3 for suitability in one of our products, and I'm experiencing an annoying problem: it seems like a lone pixel is brighter than several consecutive pixels.

See the attached image for an example. All lit pixels are set to the same brightness value, but the ones that form a row are a lot dimmer than the one with no (horizontally) adjacent pixels such as the ones in the text "Hej Lowe". You can see variations even in the text, although it's not as obvious.

I've tried tweaking the init parameters for the screen to compensate for this, but so far I haven't found anything that makes a difference. I'm using the suggested init values from the documentation and example code.

It's like there's a per-row energy budget that gets distributed among the lit pixels.

ps. The captcha is horrible. I've failed five times trying to post this.

Paul_B

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Re: NHD-2.7-12864UCY3 Uneven brightness depending on neighboring pixels
« Reply #1 on: October 20, 2016, 08:06:54 AM »
Thank you for the information, since the NHD-2.7-12864UCY3 is a Monochrome Passive-Matrix OLED display unfortunately the slight change in luminance is a characteristic of this OLED technology. To illuminate any particular pixel line in a passive-matrix display, electrical signals are applied to the row line and column line. The more current pumped through each pixel diode, the brighter the pixel.

Iíve heard of customers implementing some software correction routines to help with this issue when using monochrome OLED displays, by way of increasing/decreasing the grayscale (brightness) value of a particular pixel based on how many pixels are ON in that row.


mikaeleiman

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Re: NHD-2.7-12864UCY3 Uneven brightness depending on neighboring pixels
« Reply #2 on: October 21, 2016, 08:19:48 AM »
I tested with a simple "adjust pixel value based on lit pixels per row" thing, it turned out somewhat ok - see attached image. With a bit more tuning it could probably be improved a bit further.

To improve brightness (since this forces pixels values down to about half of max for single pixels), I increased the SET_PRECHARGE_VOLTAGE value from 0x10 to 0x25, which seems to result in a brightness about equal to what single pixels have with the default value. Is this something that will result in display damage or degradation over time, and lower screen lifetime, or is that mainly determined by pixel brightness over time?

mikaeleiman

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Re: NHD-2.7-12864UCY3 Uneven brightness depending on neighboring pixels
« Reply #3 on: November 22, 2016, 06:16:42 AM »
To improve brightness (since this forces pixels values down to about half of max for single pixels), I increased the SET_PRECHARGE_VOLTAGE value from 0x10 to 0x25, which seems to result in a brightness about equal to what single pixels have with the default value. Is this something that will result in display damage or degradation over time, and lower screen lifetime, or is that mainly determined by pixel brightness over time?

Does anyone know if this will cause problems, or if it's safe?

 

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