Google Pixel 4a Lens Shading - Revision history

imported>Student221: /* Exposure */

2020-11-28T00:07:59Z

Exposure

← Older revision		Revision as of 00:07, 28 November 2020
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	To have a clearer comparison, we plot the mean and standard derivation of the corrected image with different exposure time in Fig. 10. It matches what we conclude from Fig. 9. The standard derivation and mean are similar for different exposure time.		To have a clearer comparison, we plot the mean and standard derivation of the corrected image with different exposure time in Fig. 10. It matches what we conclude from Fig. 9. The standard derivation and mean are similar for different exposure time.

	[[File:Jiahui_fig17.png\|600px\|center\|thumb\|'''Figure 10''': Mean and standard derivation of the corrected images with different exposure time.		[[File:Jiahui_fig17.png\|600px\|center\|thumb\|'''Figure 10''': Mean and standard derivation of the corrected images with different exposure time.]]

	===ISO speed===		===ISO speed===

imported>Student221: /* ISO speed */

2020-11-28T00:07:21Z

ISO speed

← Older revision		Revision as of 00:07, 28 November 2020
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	We now fix the exposure time and analyze the influence of the ISO speed. The ISO speed has a great influence on noise level and the total illumination. However, when we subtract the Black level illumination and normalized the data, the relative illumination curve shape should not be influenced, as shown in Fig. 11. So we can draw similar conclusions as in exposure duration study that the ISO speed won't influence the relative illumination shape thus share the same lens shading correction map.		We now fix the exposure time and analyze the influence of the ISO speed. The ISO speed has a great influence on noise level and the total illumination. However, when we subtract the Black level illumination and normalized the data, the relative illumination curve shape should not be influenced, as shown in Fig. 11. So we can draw similar conclusions as in exposure duration study that the ISO speed won't influence the relative illumination shape thus share the same lens shading correction map.

	[[File:Jiahui_fig12.png\|600px\|center\|thumb\|'''Figure 11''': We plot blue channel data with different ISO speed time with the same exposure time and cut at the center of the images. Left: Unnormalized image data with ISO speeds. Right: normalized data with ISO speeds. ]]		[[File:Jiahui_fig12.png\|600px\|center\|thumb\|'''Figure 11''': We plot blue channel data with different ISO speed time with the same exposure time and cut at the center of the images. Left: Unnormalized image data with different ISO speeds. Right: normalized data with different ISO speeds. ]]

	===Cos4th===		===Cos4th===

imported>Student221: /* ISO speed */

2020-11-28T00:06:55Z

ISO speed

← Older revision		Revision as of 00:06, 28 November 2020
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	We now fix the exposure time and analyze the influence of the ISO speed. The ISO speed has a great influence on noise level and the total illumination. However, when we subtract the Black level illumination and normalized the data, the relative illumination curve shape should not be influenced, as shown in Fig. 11. So we can draw similar conclusions as in exposure duration study that the ISO speed won't influence the relative illumination shape thus share the same lens shading correction map.		We now fix the exposure time and analyze the influence of the ISO speed. The ISO speed has a great influence on noise level and the total illumination. However, when we subtract the Black level illumination and normalized the data, the relative illumination curve shape should not be influenced, as shown in Fig. 11. So we can draw similar conclusions as in exposure duration study that the ISO speed won't influence the relative illumination shape thus share the same lens shading correction map.

	[[File:Jiahui_fig12.png\|600px\|center\|thumb\|'''Figure 11''': ~~Mean~~ and ~~standard derivation~~ of the ~~corrected~~ images with ~~different exposure time~~.]]		[[File:Jiahui_fig12.png\|600px\|center\|thumb\|'''Figure 11''': We plot blue channel data with different ISO speed time with the same exposure time and cut at the center of the images. Left: Unnormalized image data with ISO speeds. Right: normalized data with ISO speeds. ]]

	===Cos4th===		===Cos4th===

imported>Student221: /* Exposure */

2020-11-28T00:06:31Z

Exposure

← Older revision		Revision as of 00:06, 28 November 2020
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	To have a clearer comparison, we plot the mean and standard derivation of the corrected image with different exposure time in Fig. 10. It matches what we conclude from Fig. 9. The standard derivation and mean are similar for different exposure time.		To have a clearer comparison, we plot the mean and standard derivation of the corrected image with different exposure time in Fig. 10. It matches what we conclude from Fig. 9. The standard derivation and mean are similar for different exposure time.

	[[File:Jiahui_fig17.png\|600px\|center\|thumb\|'''Figure 10''': ~~We plot blue channel data with different ISO speed time with the same exposure time~~ and ~~cut at the center~~ of the images~~. Left: Unnormalized image data~~ with ~~ISO speeds. Right: normalized data with ISO speeds~~. ]]		[[File:Jiahui_fig17.png\|600px\|center\|thumb\|'''Figure 10''': Mean and standard derivation of the corrected images with different exposure time.

	===ISO speed===		===ISO speed===

imported>Student221: /* ISO speed */

2020-11-28T00:05:25Z

ISO speed

← Older revision		Revision as of 00:05, 28 November 2020
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	===ISO speed===		===ISO speed===
	We now fix the exposure time and ~~analysis~~ the influence of the ISO speed. The ISO speed has a great influence on noise level and the total illumination. However, when we subtract the Black level illumination and normalized the data, the relative illumination curve shape should not be influenced, as shown in Fig. 11. So we can draw similar conclusions as in exposure duration study that the ISO speed won't influence the relative illumination shape thus share the same lens shading correction map.		We now fix the exposure time and analyze the influence of the ISO speed. The ISO speed has a great influence on noise level and the total illumination. However, when we subtract the Black level illumination and normalized the data, the relative illumination curve shape should not be influenced, as shown in Fig. 11. So we can draw similar conclusions as in exposure duration study that the ISO speed won't influence the relative illumination shape thus share the same lens shading correction map.

	[[File:Jiahui_fig12.png\|600px\|center\|thumb\|'''Figure 11''': Mean and standard derivation of the corrected images with different exposure time.]]		[[File:Jiahui_fig12.png\|600px\|center\|thumb\|'''Figure 11''': Mean and standard derivation of the corrected images with different exposure time.]]

imported>Student221: /* Exposure */

2020-11-28T00:04:20Z

Exposure

← Older revision		Revision as of 00:04, 28 November 2020
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	===Exposure===		===Exposure===
	We are going to fix the ISO speed first (isospeed=198 in analysis). There are 5 unique exposure durations, each has 5 sampled images with the same ISO speed. We are going to average the 5 samples with the same exposure duration and same ISO speed.		We are going to fix the ISO speed first (isospeed=198 in analysis). There are 5 unique exposure durations, each has 5 sampled images with the same ISO speed. We are going to average the 5 samples with the same exposure duration and same ISO speed.
	In Fig. 8, we plot the normalized and unnormalized blue channel illumination data cutting at the center of the images.		In Fig. 8, we plot the normalized and unnormalized blue channel illumination data cutting at the center (y=0) of the images.

	[[File:Jiahui_fig15.png\|600px\|center\|thumb\|'''Figure 8''': We plot blue channel data with different exposure time with ISO198 at the center of the images. Left: Unnormalized image data with different exposure time. Right: normalized data with different exposure time. ]]		[[File:Jiahui_fig15.png\|600px\|center\|thumb\|'''Figure 8''': We plot blue channel data with different exposure time with ISO198 at the center of the images. Left: Unnormalized image data with different exposure time. Right: normalized data with different exposure time. ]]

imported>Student221: /* ISO speed */

2020-11-28T00:03:11Z

ISO speed

← Older revision		Revision as of 00:03, 28 November 2020
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	===ISO speed===		===ISO speed===
	We now fix the exposure time and analysis the influence of the ISO speed. The ISO speed has a great influence on noise level and the total illumination. However, when we subtract the Black level illumination and normalized the data, the ~~The provided data has a small number of ISO with the same exposure time~~. We can ~~only find at most 3 iso speeds with the same exposure. We then perform~~ similar ~~analysis~~ as in ~~the~~ exposure duration~~. You may find~~ the ~~data and figures in the supplementary slides and codes. The conclusion is that,~~ ISO speed ~~seems to have a larger~~ influence to the correction map~~, which might be better to re-fit the model with different iso speeds~~.		We now fix the exposure time and analysis the influence of the ISO speed. The ISO speed has a great influence on noise level and the total illumination. However, when we subtract the Black level illumination and normalized the data, the relative illumination curve shape should not be influenced, as shown in Fig. 11. So we can draw similar conclusions as in exposure duration study that the ISO speed won't influence the relative illumination shape thus share the same lens shading correction map.

	[[File:Jiahui_fig12.png\|600px\|center\|thumb\|'''Figure 11''': Mean and standard derivation of the corrected images with different exposure time.]]		[[File:Jiahui_fig12.png\|600px\|center\|thumb\|'''Figure 11''': Mean and standard derivation of the corrected images with different exposure time.]]


	===Cos4th===		===Cos4th===

imported>Student221: /* Conclusions */

2020-11-27T23:59:05Z

Conclusions

← Older revision		Revision as of 23:59, 27 November 2020
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	== Conclusions ==		== Conclusions ==
	In conclusion, we have explored different polynomial models for lens shading correction under different conditions. The results show that the lens shading may be corrected better with higher order polynomial function. We conclude that, when performing the raw image processing, one needs to separate color channels and subtract the Black Level intensity before processing the data.		In conclusion, we have explored different polynomial models for lens shading correction under different conditions. The results show that the lens shading may be corrected better with higher order polynomial function. We conclude that, when performing the raw image processing, one needs to separate color channels and subtract the Black Level intensity before processing the data.
	For different exposure ~~duration~~ and ISO ~~speed~~, one might use the same lens shading correction map with relative illumination and correct data normalization methods.		For different exposure durations and ISO speeds, one might use the same lens shading correction map with relative illumination and correct data normalization methods.
	The lens shading is caused by the intrinsic lens geometric distortion. The optical system is linear, so this phenomenon is intrinsic and should not depend on the illumination intensity.		The lens shading is caused by the intrinsic lens geometric distortion. The optical system is linear, so this phenomenon is intrinsic and should not depend on the illumination intensity.
	There are some other issues we meet during the data analysis process.		There are some other issues we meet during the data analysis process.

imported>Student221: /* Black Level and Relative illumination */

2020-11-27T23:57:13Z

Black Level and Relative illumination

← Older revision		Revision as of 23:57, 27 November 2020
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	If we do not subtract the black level intensity, what we actually calculate is		If we do not subtract the black level intensity, what we actually calculate is
	<center> <math> (E_{\theta}+Black)/( E_0+Black) </math>, </center>		<center> <math> (E_{\theta}+Black)/( E_0+Black) </math>, </center>
	which gives a wrong ~~fitting~~ conclusions that Black level intensity and the absolute intensity will influence the line shape and fitting parameters.		which gives a wrong conclusions that Black level intensity and the absolute intensity will influence the line shape and fitting parameters.

	Thus it is important to subtract the black level intensity and use the relative illumination to calculate the lens shading correction map.		Thus it is important to subtract the black level intensity and use the relative illumination to calculate the lens shading correction map.

imported>Student221: /* Black Level and Relative illumination */

2020-11-27T23:56:47Z

Black Level and Relative illumination

← Older revision		Revision as of 23:56, 27 November 2020
Line 68:		Line 68:
	If we do not subtract the black level intensity, what we actually calculate is		If we do not subtract the black level intensity, what we actually calculate is
	<center> <math> (E_{\theta}+Black)/( E_0+Black) </math>, </center>		<center> <math> (E_{\theta}+Black)/( E_0+Black) </math>, </center>
	which ~~means~~ Black level intensity and the absolute intensity will influence the line shape and fitting parameters.		which gives a wrong fitting conclusions that Black level intensity and the absolute intensity will influence the line shape and fitting parameters.

	Thus it is important to subtract the black level intensity and use the relative illumination to calculate the lens shading correction map.		Thus it is important to subtract the black level intensity and use the relative illumination to calculate the lens shading correction map.