Display pattern inversion using internal patterns

Ku,

I am very sorry that I missed responding to your message. I need to look into this and understand what is going on. I will respond to you as soon as possible.

Best regards,

Pascal

Hello Pascal,

Thank you for clarifying the script for internal patterns. I can understand the i2c protocol better now.

We are trying to study the flicker fusion threshold for human eyes when using structured light patterns. We are hoping that by inverting the patterns at a rate in the range of 100Hz-600Hz, the projected light can appear completely steady to human eyes and that any flickering is not perceived by the human eyes.

I intentionally 'slow down' the internal patterns to inverting rates of 150Hz, 300Hz, and 600Hz.

As expected, when I try to invert the patterns at a rate of 150Hz, my eyes can notice the patterns are swithcing

When I increase the inverting rate to 600Hz, my eyes only see uniform display and can no longer see the patterns that are being used.

However, there is a very disturbing artifact that I can notice with my eyes at all three frequencies. That is, my eyes can notice vertical streaks appearing on the display at about every 2 seconds interval. The location of the vertical streaks seem to correspond to the boundary location between the ON and OFF light pattern. Please see below for examples. I used Photoshop to edit the display to illustrate what my eyes see. I was not able to capture these streaks with my camera even when I prolong the camera exposure time to 2- 3 seconds.

Can you offer some explanations why there may be vertical streaks when inverting patterns? For our applications, it is very important that the human eyes perceive only a homogeneous display with no flickering and no streaks.

I can only hypothesize. But if you can offer any comments, that would be greatly appreciated.

My current guess is that each subsequent internal pattern is displayed with slightly unequal brightness and my eyes are picking up the subtle difference in signal intensity between each repeating patterns.

Thank you

The scripts that were used to generate the above conditions are as followed (similar to what you suggested except I set different instruction for subaddress xD3, xD4)

Script:

bus3-i2c 0x1b wb4 0x24 0x00000000

bus3-i2c 0x1b wb4 0x1F 0x0000000A (set display mode to 1200Hz)

bus3-i2c 0x1b wb4 0xBE 0x00000040

if inverting patterns at a rate of 1200/8=150Hz, then I run this

bus3-i2c 0x1b wb4 0xD3 0x00000000

bus3-i2c 0x1b wb4 0xD4 0x000000FF

if inverting patterns at a rate of 1200/4=300Hz, then I run this

bus3-i2c 0x1b wb4 0xD3 0x0000000F

bus3-i2c 0x1b wb4 0xD4 0x0000000F

if inverting patterns at a rate of 1200/2=600Hz, then I run this

bus3-i2c 0x1b wb4 0xD3 0x00000033

bus3-i2c 0x1b wb4 0xD4 0x00000033

bus3-i2c 0x1b wb4 0xD7 0x00000011

bus3-i2c 0x1b wb4 0xD8 0x00000011

bus3-i2c 0x1b wb4 0xD9 0x00000011

bus3-i2c 0x1b wb4 0xDA 0x00000011

bus3-i2c 0x1b wb4 0xDB 0x00000011

bus3-i2c 0x1b wb4 0xDC 0x00000011

bus3-i2c 0x1b wb4 0xDD 0x00000011

bus3-i2c 0x1b wb4 0xDE 0x00000011

bus3-i2c 0x1b wb4 0x29 0x00000000

bus3-i2c 0x1b wb4 0xD2 0x00000000

bus3-i2c 0x1b wb4 0xD2 0x000000F1 (this is repeating 16 patterns)

bus3-i2c 0x1b wb4 0x29 0x00000001

Ku

Ku,

I do believe that I have an explanation for what you are seeing. It is not a "glitch" in the pattern, or the hardware. It is your eyes! Your eyes naturally exhibit quick, jerky movements, one of which is called a saccade. The evolutionary function of this is to "dither" the image on the retina to sharpen and refresh the image processed by the retina/brain. If you stare at something for several seconds, and suppress the saccade, your visual field will become de-sensitised.

These saccade movements make it look like there are glitches in the patterns which are being projected in rapid sequence. This is entirely an effect of the eyes' motions interacting with the patterns position as seen on the retina.

Try looking at the patterns and intentionally jerking your eye position. See if you can induce these artifacts.

Perhaps this is it.

Best regards,

Pascal

Hi Pascal,

It is fun that a discussion about the pico projector turns into a discussion about vision and neuroscience.

Your explanation seems to make sense.  The vertical streaks seem to appear more frequently with more frequent blinking. 

If I use finer patterns with only 2-4 pixels stripe width and its inversion, instead of observing steaks between patterns boundary, I would notice that the original patterns jump out at me every 2 seconds. It seems like this is due to saccadic masking causing the stopped clock illusion.

Is it possible to minimize this effect when using the structured light patterns? Our current hypothesis is that we may reduce this stopped-clock illusion if we cycle through as many different patterns as we can in specific sequence. Have you come across possible strategies before?

If not, does Texas Instrument provide pico projector that provides light patterns outside of visible spectrum?

Finally, on page 14 of the Pico kit application report, it says that "the internal pattern generator supports up to a 32 frame deep repeating pattern set". However, I am not clear how by only choosing up to 15 choices of patterns allow display of 32 frames of different patterns.

On page 28 of the chipset programmer's guide, 5 bits (bit 8:4) of of xD2 is allocated to set the number of patterns minus one that will be displayed before pattern sequence repeats. 

Does this mean if I want to display beyond the 17th pattern using 

bus3-i2c 0x1b wb4 0xDF 0x00000055
bus3-i2c 0x1b wb4 0xE0 0x00000055

bus3-i2c 0x1b wb4 0xE1 0x00000066
bus3-i2c 0x1b wb4 0xE2 0x00000066

bus3-i2c 0x1b wb4 0xE3 0x00000077
bus3-i2c 0x1b wb4 0xE4 0x00000077

bus3-i2c 0x1b wb4 0xE5 0x00000088
bus3-i2c 0x1b wb4 0xE6 0x00000088

I will need to set the maximum number of different patterns possible is by using the i2c command like this:

bus3-i2c 0x1b wb4 0xD2 0x000001F1 (this means 31+1 patterns, right)

Thank you

Best,

Ku

Thank you Pascal for all your help and suggestions

I got a LightCommander to play with now.

Best,

Ku

Great!

Pascal