Shadows in the corner of tablet  - Page 1
Forum section: electronics / projects

author: autobot
author_rank: Regular Contributor
timestamp: May 04, 2015, 03:29:36 pm
content: Hi,Bought a new cheap chinese tablet. Great spec for the price. But it has a problem with black round shadows in the corners, more visible when the screen is more lit.So why does this happen? what's the technical name ? does this problem gets worse over time ? or except the corner shadows, this in general should have no effect on the display long term ?Thanks.

author: ChristofferB
author_rank: Frequent Contributor
timestamp: May 04, 2015, 04:13:06 pm
content: Not sure, could it just be uneven backlight? does the touch screen work in the areas?

author: autobot
author_rank: Regular Contributor
timestamp: May 04, 2015, 05:19:17 pm
content: Yes , the touch screen seems to work in the corners. Also , if it's helpful , it's an IPS screen.

author: miguelvp
author_rank: Super Contributor
timestamp: May 05, 2015, 01:39:08 am
content: A picture is worth a thousand words

author: Niklas
author_rank: Frequent Contributor
timestamp: May 05, 2015, 05:42:37 am
content: My guess is that you have rows of backlight LEDs along the edges of the display that lights up a plastic sheet from the sides. The emitted light pattern from each LED is spreading out at an angle. Take a paper, draw a rectangle 10x5 cm and mark every cm along the edges but not at the corners. From each marked location, draw a 3 cm long triangle that spreads 3 cm. You will see that most of the rectangle will have overlaps, but not at the edges or in the corners.In order to save money they have not placed LEDs at the corners of the display. The technically best position would probably be at 45 degrees, which would differ from the rest of the LEDs and add cost.On DSLRs you can find a similar problem, called vignetting, caused by a circular beam light that lights up a square sensor. The vignetting is more significant when the lens is stopped down (higher F-stop value, F11, F16...) which corresponds to a smaller diameter of the light beam that hits the sensor. The workaround is to apply a correction, as part of a lens correction profile, in the post processing.

author: electr_peter
author_rank: Unknown
timestamp: May 05, 2015, 06:49:29 am
content: Three possible suspects:tablet screen is designed badly and have black corners by defaultback-lighting sheets delaminated or there is some gapLEDs are not functioning in the corners - I have experienced this myself with laptop screens

author: dexters_lab
author_rank: Unknown
timestamp: May 05, 2015, 06:53:36 am
content: stress to the LCD panel can cause all sorts of colour shifts and shadowing effects, this can also happen if the case is not quite true or the glue isn't applied evenly to stick the panel to the chassis

author: autobot
author_rank: Regular Contributor
timestamp: May 05, 2015, 10:38:23 am
content: Thanks for the answers!Picture is here :https://drive.google.com/file/d/0B3THJMD3YeKbeGdDazFQWGxUSU10S1d5RE1NdEJGcG9ZZXRJ/view?usp=sharingAnd from all the answers i get that it's usually doesn't get worse with time ?

author: electr_peter
author_rank: Unknown
timestamp: May 05, 2015, 11:19:51 am
content: Quote from: autobot on May 05, 2015, 10:38:23 amIf LEDs are burning out or backlight sheets are delaminating, then it could get worse sooner or later.