Camera Image Quality Metrics (Sharpness) - Revision history

imported>Projects221: /* Experiments and Results */

2014-03-20T05:15:34Z

Experiments and Results

← Older revision		Revision as of 05:15, 20 March 2014
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	[[File:Dish-psize-1_5_10.png \|center\|800x600px]]		[[File:Dish-psize-1_5_10.png \|center\|800x600px]]

	One more observation is that when pixel size is large, there are some "bumps" in acutance values. In the following images we vary the pixel size from 7 micrometer to 9 micrometer. Although the image in the middle corresponds to the largest acutance value, it still looks blurrier ~~that~~ the first image on the left. This suggests that acutance might not be a very accurate metric when pixel size is large.		One more observation is that when pixel size is large, there are some "bumps" in acutance values. In the following images we vary the pixel size from 7 micrometer to 9 micrometer. Although the image in the middle corresponds to the largest acutance value, it still looks blurrier than the first image on the left. This suggests that acutance might not be a very accurate metric when pixel size is large.
	[[File:Mcbeth-psize-7_8_9.png \|center\|800x600px]]		[[File:Mcbeth-psize-7_8_9.png \|center\|800x600px]]

imported>Projects221: /* Experiments and Results */

2014-03-20T05:13:29Z

Experiments and Results

← Older revision		Revision as of 05:13, 20 March 2014
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	==Experiments and Results==		==Experiments and Results==
	To explore whether MTF50 and Acutance correlates well with human viewing experience, we selected 4 different types of scene: landscape, fruit, color checker and human face. As we vary f/# from 1 to 10 and pixel size from 1 to 10 micrometer, we ~~would~~ generate 100 groups of data. For each combination we ~~would~~ keep the mean illuminance at 100 Candelas/m2, field of view at 5 degree and viewing distance at 1m. Then we measure MTF50 and Acutance against a B/W slanted bar and generate actual images on the above 4 different scenes.		To explore whether MTF50 and Acutance correlates well with human viewing experience, we selected 4 different types of scene: landscape, fruit, color checker and human face. As we vary f/# from 1 to 10 and pixel size from 1 to 10 micrometer, we generate 100 groups of data. For each combination we keep the mean illuminance at 100 Candelas/m2, field of view at 5 degree and viewing distance at 1m. Then we measure MTF50 and Acutance against a B/W slanted bar and generate actual images on the above 4 different scenes.

	Below is a plot of MTF50 and acutance against F/# and pixel size. As we can see both MTF50 and acutance benefit from lower F/# and smaller pixel size. Also both metrics vary a lot in our sweep range.		Below is a plot of MTF50 and acutance against F/# and pixel size. As we can see both MTF50 and acutance benefit from lower F/# and smaller pixel size. Also both metrics vary a lot in our sweep range.

imported>Projects221: /* Methods */

2014-03-20T05:12:08Z

Methods

← Older revision		Revision as of 05:12, 20 March 2014
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	==Methods==		==Methods==
	The Modulation Transfer Function (MTF) is defined as the normalized magnitude of the Fourier Transform of the imaging system’s point spread function. Practically,it is a metric quantifying the sharpness of the image over the range of special frequencies below Nyquist frequency of the system. We measured the system MTF using the ISO standard ISO 12233. This method uses a B/W slanted bar image as the test scene and then measure the response on a rectangular area at the edge to estimate the system MTF. MTF50 is a specific value which indicate the spatial frequency where the amplitude of MTF curve fall to 50% of the maximum amplitude.		The Modulation Transfer Function (MTF) is defined as the normalized magnitude of the Fourier Transform of the imaging system’s point spread function. Practically,it is a metric quantifying the sharpness of the image over the range of special frequencies below Nyquist frequency of the system. We measured the system MTF using the ISO standard ISO 12233. This method uses a B/W slanted bar image as the test scene and then measure the response on a rectangular area at the edge to estimate the system MTF. MTF50 is a specific value which indicate the spatial frequency where the amplitude of MTF curve fall to 50% of the maximum amplitude. We also used Acutance, which is calculated using the lens's frequency response and an ISO12233 specific weighting function. Acutance measures the edge sharpness of a picture.

	We uses the Image Systems Evaluation Toolkit (ISET) to simulate the image system response in MATLAB. This software set consists of four modules: Scene, Optics, Sensor, and Processor. The Scene module represents the input scene as a multidimensional spectral radiance array at each pixel. The Optics module converts the scene radiance data into an irradiance image through the optics. The Sensor module then transform the irradiance to sensor signal using a model account for both optical and electrical properties of the sensor and pixel. The Processor module finally transforms the electrons on each pixels into a digital image that is rendered for a color display. This module includes algorithms for demosaicing, color conversion to a calibrated color space, and color balancing.		We uses the Image Systems Evaluation Toolkit (ISET) to simulate the image system response in MATLAB. This software set consists of four modules: Scene, Optics, Sensor, and Processor. The Scene module represents the input scene as a multidimensional spectral radiance array at each pixel. The Optics module converts the scene radiance data into an irradiance image through the optics. The Sensor module then transform the irradiance to sensor signal using a model account for both optical and electrical properties of the sensor and pixel. The Processor module finally transforms the electrons on each pixels into a digital image that is rendered for a color display. This module includes algorithms for demosaicing, color conversion to a calibrated color space, and color balancing.

	We first evaluate the sensitivities of each parameter of the image system to the final image quality. As a result, the F# and pixel size of the sensor changes the sharpness of image a lot and the effect of other parameters as photon noise, view distance and luminance are insignificant. By sweeping F# and pixel size, we obtain the metric values of MTF50 and acutance for each settings. Then for each specific setting, we simulate the response image using multispectral data of actual scenes. In this project, we choose the image data of face, fruit and landscape to test.		We first evaluate the sensitivities of each parameter of the image system to the final image quality. As a result, the F# and pixel size of the sensor changes the sharpness of image a lot and the effect of other parameters as photon noise, view distance and luminance are insignificant. By sweeping F# and pixel size, we obtain the metric values of MTF50 and acutance for each settings. Then for each specific setting, we simulate the response image using multispectral data of actual scenes. In this project, we choose the image data of face, fruit and landscape to test.

	==Experiments and Results==		==Experiments and Results==

imported>Projects221: /* Experiments and Results */

2014-03-20T04:49:37Z

Experiments and Results

← Older revision		Revision as of 04:49, 20 March 2014
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	Finally we keep F/# fixed at 1 and vary pixel size. As we can see from the following image, the increasing of pixel size significantly lowered image quality. The effect is more severe than increasing F/#		Finally we keep F/# fixed at 1 and vary pixel size. As we can see from the following image, the increasing of pixel size significantly lowered image quality. The effect is more severe than increasing F/#
			[[File:Fix-fn.png \|center\|800x600px]]
	[[File:Dish-psize-1_5_10.png \|center\|800x600px]]		[[File:Dish-psize-1_5_10.png \|center\|800x600px]]

imported>Projects221: /* Experiments and Results */

2014-03-20T04:48:24Z

Experiments and Results

← Older revision		Revision as of 04:48, 20 March 2014
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	[[File:Dish-psize-1_5_10.png \|center\|800x600px]]		[[File:Dish-psize-1_5_10.png \|center\|800x600px]]

	One more observation is that when pixel size is large, there are some "bumps" in acutance values. In the following images we vary the pixel size from 7 micrometer to 9 micrometer. Although the image in the middle corresponds to the largest acutance value, it still looks blurrier that the first image on the left.		One more observation is that when pixel size is large, there are some "bumps" in acutance values. In the following images we vary the pixel size from 7 micrometer to 9 micrometer. Although the image in the middle corresponds to the largest acutance value, it still looks blurrier that the first image on the left. This suggests that acutance might not be a very accurate metric when pixel size is large.
	[[File:Mcbeth-psize-7_8_9.png \|center\|800x600px]]		[[File:Mcbeth-psize-7_8_9.png \|center\|800x600px]]

imported>Projects221: /* Experiments and Results */

2014-03-20T04:45:12Z

Experiments and Results

← Older revision		Revision as of 04:45, 20 March 2014
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	[[File:Face-f--1_5_10.png \|center\|800x600px]]		[[File:Face-f--1_5_10.png \|center\|800x600px]]

			Finally we keep F/# fixed at 1 and vary pixel size. As we can see from the following image, the increasing of pixel size significantly lowered image quality. The effect is more severe than increasing F/#
	[[File:Dish-psize-1_5_10.png \|center\|800x600px]]		[[File:Dish-psize-1_5_10.png \|center\|800x600px]]

			One more observation is that when pixel size is large, there are some "bumps" in acutance values. In the following images we vary the pixel size from 7 micrometer to 9 micrometer. Although the image in the middle corresponds to the largest acutance value, it still looks blurrier that the first image on the left.
	[[File:Mcbeth-psize-7_8_9.png \|center\|800x600px]]		[[File:Mcbeth-psize-7_8_9.png \|center\|800x600px]]

imported>Projects221: /* Experiments and Results */

2014-03-20T04:40:32Z

Experiments and Results

← Older revision		Revision as of 04:40, 20 March 2014
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	[[File:Acutance_vs_mtf50.png\|center\|800x600px]]		[[File:Acutance_vs_mtf50.png\|center\|800x600px]]

	Now we start to analyze the effect of degrading metrics on real images. In the following scenes we can see that as MTF50 and acutance becomes smaller, all the images become ~~more and more blurry~~. One interesting observation is that MTF50 is not a linear metric. In these images, as F/# increases from 1 to 5, MTF50 has degraded by about 250. As F/# increases from 5 to 10, MTF50 has degraded by only 60. ~~Although~~ the difference in ~~MTF50~~ value ~~is different~~, the images demonstrated similar sharpness difference when F/# varies from 1 to 5 and 5 to 10.		Now we start to analyze the effect of degrading metrics on real images. In the following scenes we can see that as MTF50 and acutance becomes smaller, all the images become blurrier. One interesting observation is that MTF50 is not a linear metric. In these images, as F/# increases from 1 to 5, MTF50 has degraded by about 250. As F/# increases from 5 to 10, MTF50 has degraded by only 60. Despite the difference in metrics value, the images demonstrated similar sharpness difference when F/# varies from 1 to 5 and 5 to 10.
	[[File:Fix-pixel-size.png \|center\|800x600px]]		[[File:Fix-pixel-size.png \|center\|800x600px]]
	[[File:Dish-f--1_5_10.png \|center\|800x600px]]		[[File:Dish-f--1_5_10.png \|center\|800x600px]]

imported>Projects221: /* Experiments and Results */

2014-03-20T04:38:39Z

Experiments and Results

← Older revision		Revision as of 04:38, 20 March 2014
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	[[File:LoResFemale5_Cx.png\|center\|800x600px]]		[[File:LoResFemale5_Cx.png\|center\|800x600px]]

	Below is a plot of MTF50 against acutance when pixel size is fixed at 1 micrometer and F/# is varied from 1 to 10.		Below is a plot of MTF50 against acutance when pixel size is fixed at 1 micrometer and F/# is varied from 1 to 10. These two metrics are correlated.
	[[File:Acutance_vs_mtf50.png\|center\|800x600px]]		[[File:Acutance_vs_mtf50.png\|center\|800x600px]]

imported>Projects221: /* Experiments and Results */

2014-03-20T04:37:58Z

Experiments and Results

← Older revision		Revision as of 04:37, 20 March 2014
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	==Experiments and Results==		==Experiments and Results==
	To explore whether MTF50 and Acutance correlates well with human viewing experience, we selected 4 different types of scene: landscape, fruit, color checker and human face. As we vary f/# from 1 to 10 and pixel size from 1 to 10 micrometer, we would generate 100 groups of data. For each combination we would keep the mean illuminance at 100 Candelas/m2, field of view at 5 degree and viewing distance at 1m. Then we measure MTF50 and Acutance against a B/W slanted bar and generate actual images on the above 4 different scenes.		To explore whether MTF50 and Acutance correlates well with human viewing experience, we selected 4 different types of scene: landscape, fruit, color checker and human face. As we vary f/# from 1 to 10 and pixel size from 1 to 10 micrometer, we would generate 100 groups of data. For each combination we would keep the mean illuminance at 100 Candelas/m2, field of view at 5 degree and viewing distance at 1m. Then we measure MTF50 and Acutance against a B/W slanted bar and generate actual images on the above 4 different scenes.

			Below is a plot of MTF50 and acutance against F/# and pixel size. As we can see both MTF50 and acutance benefit from lower F/# and smaller pixel size. Also both metrics vary a lot in our sweep range.
	[[File:LoResFemale5_Cx.png\|center\|800x600px]]		[[File:LoResFemale5_Cx.png\|center\|800x600px]]
	~~Plots of MTF50 and acutance against F/# and pixel size. As we can see both MTF50 and acutance benefit from lower F/# and smaller pixel size. Also both metrics vary a lot in our sweep range.~~

			Below is a plot of MTF50 against acutance when pixel size is fixed at 1 micrometer and F/# is varied from 1 to 10.
	[[File:Acutance_vs_mtf50.png\|center\|800x600px]]		[[File:Acutance_vs_mtf50.png\|center\|800x600px]]
	~~Plots of MTF50 against acutance when pixel size is fixed at 1 micrometer and F/# is varied from 1 to 10.~~

			Now we start to analyze the effect of degrading metrics on real images. In the following scenes we can see that as MTF50 and acutance becomes smaller, all the images become more and more blurry. One interesting observation is that MTF50 is not a linear metric. In these images, as F/# increases from 1 to 5, MTF50 has degraded by about 250. As F/# increases from 5 to 10, MTF50 has degraded by only 60. Although the difference in MTF50 value is different, the images demonstrated similar sharpness difference when F/# varies from 1 to 5 and 5 to 10.
	[[File:Fix-pixel-size.png \|center\|800x600px]]		[[File:Fix-pixel-size.png \|center\|800x600px]]
	[[File:Dish-f--1_5_10.png \|center\|800x600px]]		[[File:Dish-f--1_5_10.png \|center\|800x600px]]
	[[File:Mcbeth-f--1_5_10.png \|center\|800x600px]]		[[File:Mcbeth-f--1_5_10.png \|center\|800x600px]]
	[[File:Tomato-f--1_5_10.png \|center\|800x600px]]		[[File:Tomato-f--1_5_10.png \|center\|800x600px]]
	Now we start to analyze the effect of degrading metrics on real images. In the above scenes we can see that as MTF50 and acutance becomes smaller, all the images become more and more blurry. One interesting observation is that MTF50 is not a linear metric. In the images above, as F/# increases from 1 to 5, MTF50 has degraded by about 250. As F/# increases from 5 to 10, MTF50 has degraded by only 60. Although the difference in MTF50 value is different, the images demonstrated similar sharpness difference when F/# varies from 1 to 5 and 5 to 10.

			The other interesting observation is that a lower MTF50 and acutance can actually make human face images look better. This blurriness can make the image look "softer" and provide a better viewing experience.
	[[File:Face-f--1_5_10.png \|center\|800x600px]]		[[File:Face-f--1_5_10.png \|center\|800x600px]]

imported>Projects221: /* Experiments and Results */

2014-03-20T04:33:19Z

Experiments and Results

← Older revision		Revision as of 04:33, 20 March 2014
Line 26:		Line 26:
	[[File:Fix-pixel-size.png \|center\|800x600px]]		[[File:Fix-pixel-size.png \|center\|800x600px]]
	[[File:Dish-f--1_5_10.png \|center\|800x600px]]		[[File:Dish-f--1_5_10.png \|center\|800x600px]]
	~~[[File:Face-f--1_5_10.png \|center\|800x600px]]~~
	~~[[File:Dish-f--6_8_10.png \|center\|800x600px]]~~
	~~[[File:Face-f--6_8_10.png \|center\|800x600px]]~~
	[[File:Mcbeth-f--1_5_10.png \|center\|800x600px]]		[[File:Mcbeth-f--1_5_10.png \|center\|800x600px]]
	~~[[File:Mcbeth-f--6_8_10.png \|center\|800x600px]]~~
	[[File:Tomato-f--1_5_10.png \|center\|800x600px]]		[[File:Tomato-f--1_5_10.png \|center\|800x600px]]
	[[File:~~Tomato~~-f--~~6_8_10~~.png \|center\|800x600px]]		Now we start to analyze the effect of degrading metrics on real images. In the above scenes we can see that as MTF50 and acutance becomes smaller, all the images become more and more blurry. One interesting observation is that MTF50 is not a linear metric. In the images above, as F/# increases from 1 to 5, MTF50 has degraded by about 250. As F/# increases from 5 to 10, MTF50 has degraded by only 60. Although the difference in MTF50 value is different, the images demonstrated similar sharpness difference when F/# varies from 1 to 5 and 5 to 10.

			[[File:Face-f--1_5_10.png \|center\|800x600px]]

	[[File:Dish-psize-1_5_10.png \|center\|800x600px]]		[[File:Dish-psize-1_5_10.png \|center\|800x600px]]
	[[File:Mcbeth-psize-7_8_9.png \|center\|800x600px]]		[[File:Mcbeth-psize-7_8_9.png \|center\|800x600px]]

← Older revision		Revision as of 04:33, 20 March 2014
Line 26:		Line 26:
	[[File:Fix-pixel-size.png \|center\|800x600px]]		[[File:Fix-pixel-size.png \|center\|800x600px]]
	[[File:Dish-f--1_5_10.png \|center\|800x600px]]		[[File:Dish-f--1_5_10.png \|center\|800x600px]]
	~~[[File:Face-f--1_5_10.png \|center\|800x600px]]~~
	~~[[File:Dish-f--6_8_10.png \|center\|800x600px]]~~
	~~[[File:Face-f--6_8_10.png \|center\|800x600px]]~~
	[[File:Mcbeth-f--1_5_10.png \|center\|800x600px]]		[[File:Mcbeth-f--1_5_10.png \|center\|800x600px]]
	~~[[File:Mcbeth-f--6_8_10.png \|center\|800x600px]]~~
	[[File:Tomato-f--1_5_10.png \|center\|800x600px]]		[[File:Tomato-f--1_5_10.png \|center\|800x600px]]
	[[File:~~Tomato~~-f--~~6_8_10~~.png \|center\|800x600px]]		Now we start to analyze the effect of degrading metrics on real images. In the above scenes we can see that as MTF50 and acutance becomes smaller, all the images become more and more blurry. One interesting observation is that MTF50 is not a linear metric. In the images above, as F/# increases from 1 to 5, MTF50 has degraded by about 250. As F/# increases from 5 to 10, MTF50 has degraded by only 60. Although the difference in MTF50 value is different, the images demonstrated similar sharpness difference when F/# varies from 1 to 5 and 5 to 10.

			[[File:Face-f--1_5_10.png \|center\|800x600px]]

	[[File:Dish-psize-1_5_10.png \|center\|800x600px]]		[[File:Dish-psize-1_5_10.png \|center\|800x600px]]
	[[File:Mcbeth-psize-7_8_9.png \|center\|800x600px]]		[[File:Mcbeth-psize-7_8_9.png \|center\|800x600px]]