Inexpensive LED Video Wall - Revision history

imported>Projects221 at 04:40, 12 December 2015

2015-12-12T04:40:20Z

← Older revision		Revision as of 04:40, 12 December 2015
Line 77:		Line 77:

	== Results ==		== Results ==
	[[File:~~LEDBeforeAfter~~.~~jpg~~\|thumb\|256px\|A ~~before and after~~ image of ~~our~~ color ~~correction process~~]]		[[File:VideoWallMacbeth.png\|thumb\|256px\|A simulated image of the raw RGB values sent to the display to render a Macbeth color chart]]
	After combining the work of Luminance Correction with the correct color space conversions, we were able to dramatically improve the color rendering of our display.		After combining the work of Luminance Correction with the correct color space conversions, we were able to dramatically improve the color rendering of our display.
	=== Color Correction Pipeline ===		=== Color Correction Pipeline ===
Line 87:		Line 87:
	# Send RGB values to the Teensy chip for distribution		# Send RGB values to the Teensy chip for distribution

	Below is a ~~Macbeth~~ color ~~chart rendered to simulate the RGB values we must send our LED wall in order to accurately display color:~~		Below is a side by side comparison of two panels, one without color correction (left) and one with (right).

	[[File:~~VideoWallMacbeth~~.~~png~~\|thumb\|512px\|none]]		[[File:LEDBeforeAfter.jpg\|thumb\|512px\|none]]

	== Conclusions ==		== Conclusions ==

imported>Projects221: /* Luminance Correction */

2015-12-11T22:30:03Z

Luminance Correction

← Older revision		Revision as of 22:30, 11 December 2015
Line 46:		Line 46:
	'''Imaging'''		'''Imaging'''

	The first step in this process was to actually attempt to record the relative illumination that each LED was outputting. We did this with a high quality camera and imaged the panels individually in full red, full green, and full blue. The largest issues we had with this step of the calibration process was the fact that the panels had to be imaged over multiple days, which can lead to slight inconsistencies in the distance between the panels and the camera. We also had issues with some panels not being wired correctly for imaging (i.e. some of our ground a power leads were improperly assembled, creating a voltage drop and shift in color), and these issues were then subsequently fixed later. The color of the affected LEDs changed significantly between the capture process and the final assembly of the display, which meant the color correction was inaccurate for these pixels. These strips are fairly evident in pictures of the finished display.		The first step in this process was to actually attempt to record the relative illumination that each LED was outputting. We did this with a high quality camera and imaged the panels individually in full red, full green, and full blue. The largest issues we had with this step of the calibration process was the fact that the panels had to be imaged over multiple days, which can lead to slight inconsistencies in the distance between the panels and the camera. We also had issues with some panels not being wired correctly for imaging (i.e. some of our ground power leads were improperly assembled, creating a voltage drop and shift in color), and these issues were then subsequently fixed later. The color of the affected LEDs changed significantly between the capture process and the final assembly of the display, which meant the color correction was inaccurate for these pixels. These strips are fairly evident in pictures of the finished display.

	[[File:LEDCorrectionResults.jpg\|thumb\|200px\|A before and after of the corrected display. Note that we closed the greatest variance between pixels by a factor of 3]]		[[File:LEDCorrectionResults.jpg\|thumb\|200px\|A before and after of the corrected display. Note that we closed the greatest variance between pixels by a factor of 3]]
Line 55:		Line 55:
	'''Correcting'''		'''Correcting'''

	The final step of process was to store these coefficients in a look up table so that the software could access color correction data on a per pixel basis.		The final step of process was to store these coefficients in a look up table so that the software could access color correction data on a per pixel basis.

	=== Color Space Conversion ===		=== Color Space Conversion ===

imported>Projects221: /* LED Sourcing */

2015-12-11T22:17:39Z

LED Sourcing

← Older revision		Revision as of 22:17, 11 December 2015
Line 26:		Line 26:
	The obvious solution to reducing costs was simply to purchase inexpensive LEDs. As stated above, commercial displays rely on LEDs that are color matched after manufacturing, resulting in astronomical costs. Since we lacked the means to obtain such LEDs, our strategy from the outset was to find the best performance to cost ratio and attempt to correct inadequacies in our software.		The obvious solution to reducing costs was simply to purchase inexpensive LEDs. As stated above, commercial displays rely on LEDs that are color matched after manufacturing, resulting in astronomical costs. Since we lacked the means to obtain such LEDs, our strategy from the outset was to find the best performance to cost ratio and attempt to correct inadequacies in our software.

	We began sampling products from a number of different vendors internationally. To meet our specification of a 20,000 pixel display, we needed to spend approximately $0.20 per LED. We also needed LEDs with a WS2811 chipset, as that allowed us to control all three colors in a single, well documented module. With the assistance of Joyce Farrell and her lab at Stanford University, we were able to measure our candidates with a color spectrometer to assess quality and consistency. The LEDs we ended up selecting were chosen for one reason in particular; while they exhibited an expected variation in luminance across approximately ~~fifty~~ samples, their wavelength output was extremely consistent, making the color correction process considerably easier.		We began sampling products from a number of different vendors internationally. To meet our specification of a 20,000 pixel display, we needed to spend approximately $0.20 per LED. We also needed LEDs with a WS2811 chipset, as that allowed us to control all three colors in a single, well documented module. With the assistance of Joyce Farrell and her lab at Stanford University, we were able to measure our candidates with a color spectrometer to assess quality and consistency. The LEDs we ended up selecting were chosen for one reason in particular; while they exhibited an expected variation in luminance across approximately twenty samples, their wavelength output was extremely consistent, making the color correction process considerably easier.

	[[File:LEDWallSoftware.png\|thumb\|200px\|Our control pipeline]]		[[File:LEDWallSoftware.png\|thumb\|200px\|Our control pipeline]]

	=== Control Architecture ===		=== Control Architecture ===
	In order to control our display, we developed a pipeline that captures video from a monitor, applies color correction, and distributes chunks of the image to specific panels. In order to accomplish this task cheaply and efficiently, we turned to popular Arduino based products for their low cost and well documented libraries.		In order to control our display, we developed a pipeline that captures video from a monitor, applies color correction, and distributes chunks of the image to specific panels. In order to accomplish this task cheaply and efficiently, we turned to popular Arduino based products for their low cost and well documented libraries.

imported>Projects221: /* Methods */

2015-12-11T22:16:05Z

Methods

← Older revision		Revision as of 22:16, 11 December 2015
Line 20:		Line 20:

	== Methods ==		== Methods ==
	[[File:LEDIntensityDistributionGraph.png\|thumb\|256px\|The spectral power distributions of approximately 50 sampled LEDs. Note the variation in power but not in wavelength for R, G, & B]]		[[File:LEDIntensityDistributionGraph.png\|thumb\|256px\|The spectral power distributions of approximately 20 sampled LEDs. Note the variation in power but not in wavelength for R, G, & B]]
	In order to meet our specifications, we devised a number of processes and investigations that served the overall processes of sourcing, manufacturing, and controlling our display. Unfortunately, detailing all of these is beyond the scope of this article, and as such, we will be focusing primarily on our methodology for color calibration and control.		In order to meet our specifications, we devised a number of processes and investigations that served the overall processes of sourcing, manufacturing, and controlling our display. Unfortunately, detailing all of these is beyond the scope of this article, and as such, we will be focusing primarily on our methodology for color calibration and control.

Line 73:		Line 73:

	=== Gamut Mapping ===		=== Gamut Mapping ===
	Early on in our research, we were concerned that our display may not be able to reproduce all of the colors in a given color space. We therefore investigated techniques for compressing color gamuts, fully expecting to include this in our mathematical operations. When measuring the SPD of our LEDs, we were happy to discover our display was capable of producing a much wider color gamut than most commercially available monitors, rendering this step unnecessary.		Early on in our research, we were concerned that our display may not be able to reproduce all of the colors in a given color space. We therefore investigated techniques for compressing color gamuts, fully expecting to include this in our mathematical operations. When measuring the SPD of our LEDs, we were happy to discover our display was capable of producing a much wider color gamut than most commercially available monitors, rendering this step unnecessary.

	== Results ==		== Results ==

imported>Projects221: /* Appendix B */

2015-12-11T22:11:29Z

Appendix B

← Older revision		Revision as of 22:11, 11 December 2015
Line 96:		Line 96:

	== Appendix B ==		== Appendix B ==
	This project was completed jointly by Stephen Hitchcock and Matt Lathrop. Almost all work was done jointly and there was no clear devsion of work for the work done for this class.		This project was completed jointly by Stephen Hitchcock and Matt Lathrop. Almost all work was done jointly, and there was no clear devsion of work for the work done for this class.

imported>Projects221: /* Appendix B */

2015-12-11T22:11:03Z

Appendix B

← Older revision		Revision as of 22:11, 11 December 2015
Line 96:		Line 96:

	== Appendix B ==		== Appendix B ==
			This project was completed jointly by Stephen Hitchcock and Matt Lathrop. Almost all work was done jointly and there was no clear devsion of work for the work done for this class.

imported>Projects221 at 13:48, 11 December 2015

2015-12-11T13:48:28Z

← Older revision		Revision as of 13:48, 11 December 2015
Line 76:		Line 76:

	== Results ==		== Results ==
			[[File:LEDBeforeAfter.jpg\|thumb\|256px\|A before and after image of our color correction process]]
	After combining the work of Luminance Correction with the correct color space conversions, we were able to dramatically improve the color rendering of our display.		After combining the work of Luminance Correction with the correct color space conversions, we were able to dramatically improve the color rendering of our display.
	=== Color Correction Pipeline ===		=== Color Correction Pipeline ===
Line 90:		Line 91:

	== Conclusions ==		== Conclusions ==
			Overall, we discovered that it is possible to build an LED video wall for significantly less than commercial alternatives. Through our experience, we have realized just how crucial accurate color rendering is both from a technical and artistic perspective. We have certainly increased both the credibility and the usefulness of our product by taking measures to ensure that colors on a computer monitor match what will eventually be sent to our display. We would like to thank Joyce Farrell, Pat Hanrahan, Michael Ramsuar, and Brian Wandell for their support of this project.

	== Appendix A ==		== Appendix A ==

	== Appendix B ==		== Appendix B ==

imported>Projects221 at 13:37, 11 December 2015

2015-12-11T13:37:52Z

← Older revision		Revision as of 13:37, 11 December 2015
Line 86:		Line 86:

	Below is a Macbeth color chart rendered to simulate the RGB values we must send our LED wall in order to accurately display color:		Below is a Macbeth color chart rendered to simulate the RGB values we must send our LED wall in order to accurately display color:
	[[File:~~Example~~.~~jpg~~]]
			[[File:VideoWallMacbeth.png\|thumb\|512px\|none]]

	== Conclusions ==		== Conclusions ==

imported>Projects221 at 13:32, 11 December 2015

2015-12-11T13:32:54Z

← Older revision		Revision as of 13:32, 11 December 2015
Line 76:		Line 76:

	== Results ==		== Results ==
			After combining the work of Luminance Correction with the correct color space conversions, we were able to dramatically improve the color rendering of our display.
			=== Color Correction Pipeline ===
			Our final process for color correction is as follows:
			# Convert captured RGB values from sRGB monitor into linear RGB
			# Correct per pixel variance using dSLR generated look up table
			# Convert clamped values into XYZ color space
			# Convert from XYZ into the RGB color space for our LEDs
			# Send RGB values to the Teensy chip for distribution

	~~=== Color Correction Pipeline ===~~		Below is a Macbeth color chart rendered to simulate the RGB values we must send our LED wall in order to accurately display color:
			[[File:Example.jpg]]

	== Conclusions ==		== Conclusions ==

imported>Projects221 at 13:23, 11 December 2015

2015-12-11T13:23:49Z

← Older revision		Revision as of 13:23, 11 December 2015
Line 57:		Line 57:

	=== Color Space Conversion ===		=== Color Space Conversion ===
			[[File:LEDGammaCurve.png\|thumb\|256px\|The SPD of our sample before and after normalization]]
	[[File:LEDSPDNormalization.png\|thumb\|256px\|The SPD of our sample before and after normalization]]		[[File:LEDSPDNormalization.png\|thumb\|256px\|The SPD of our sample before and after normalization]]

Line 73:		Line 73:

	=== Gamut Mapping ===		=== Gamut Mapping ===
			Early on in our research, we were concerned that our display may not be able to reproduce all of the colors in a given color space. We therefore investigated techniques for compressing color gamuts, fully expecting to include this in our mathematical operations. When measuring the SPD of our LEDs, we were happy to discover our display was capable of producing a much wider color gamut than most commercially available monitors, rendering this step unnecessary.

	== Results ==		== Results ==