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Author Topic: remove the Bayer data and quadruple your resolution in B&W?  (Read 6527 times)
bwana
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« Reply #20 on: March 17, 2012, 11:27:30 AM »
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tnx pointing me to your raw import plugin in your sig, djjoofa.

I am using Mac OSX SnowLeopard and PS cs5 and importing Fuji raf files taken with a Fuji x10 camera.
This camera has the EXR sensor which simultaneously captures two offset 6 mp exposures whose ev differ  by one stop. It recombines these exposures to allow increased dynamic range.
Interestingly, photoshop creates 5 different images when i open up one raf file.Find it here:
http://dl.dropbox.com/u/29887336/fuji%20x10%20test%20image/DSCF1215.RAF

One large image is full frame, 2848x2144 pixels, wherein you can clearly see the bayer array when viewing the image at 400% magnification. Then there are 4 additional images at 1424x1072, which probably represent the individual GRGB sets of the CFA.

I find many interesting things comparing these images-for example the smooth clear blue sky actually is represented by pixels whose luminance varies. Even when I open up the the processed jpg (http://dl.dropbox.com/u/29887336/fuji%20x10%20test%20image/DSCF1215.JPG),
 the sky is 'mottled'-but only of course if you 'pixel peep'.

I was hoping to get 'increased resolution' by averaging out the luminance fluctuation of the bayer array filter-lets-eliminating the screen door effect but keeping the 'pristine' photo information. Alas, as pointed out by others above, the actual luminance fluctuation depends on the frequency of the incident light, so there is no simple way to get this. In fact the processed jpg (when desaturated to give a b&w image) is better than the raw image. The concept of looking at IR frequencies to minimize spectral absorption differences of the CFA elements is interesting as just pointed out. But I imagine this would require an IR illminator and a wratten 87a filter. Without the illuminator, the photographs would be rather dark and require long exposures. Of course, with todays new sensors capable of iso 25600 with low noise(take that tri-X!), one might imagine some awesome pics. Anyway, it would make an interesting photograph printed large. Thank you
« Last Edit: March 17, 2012, 03:33:19 PM by bwana » Logged
t6b9p
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« Reply #21 on: March 17, 2012, 11:54:37 AM »
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But I imagine this would require an IR illminator and a wratten 87a filter. Without the illuminator, the photographs would be rather dark and require long exposures.

DSLR sensors are inherently sensitive to IR, remove the ICF/AA and replace it with the appropriate thickness 830nm filter and exposure times are fine. IR "illuminator" = sunlight/daylight

Outdoor in sunlight, using an 830nm converted D200, ISO 200, f/8, ~1/40s.
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bwana
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« Reply #22 on: March 17, 2012, 03:31:57 PM »
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well, after seeing what's really on the sensor, i realize how confused i really was. A D800 only has 36 million photosites so there's no way the resolution can be increased. the pixel averaging of demosaicising may add chroma info where there was none before. no new pixels can be made.and not much luminance accuracy is lost.
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joofa
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« Reply #23 on: March 18, 2012, 12:35:25 AM »
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tnx pointing me to your raw import plugin in your sig, djjoofa.

You are most welcome.

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Interestingly, photoshop creates 5 different images when i open up one raf file.Find it here:
http://dl.dropbox.com/u/29887336/fuji%20x10%20test%20image/DSCF1215.RAF

One large image is full frame, 2848x2144 pixels, wherein you can clearly see the bayer array when viewing the image at 400% magnification. Then there are 4 additional images at 1424x1072, which probably represent the individual GRGB sets of the CFA.

Yes, the 2848x2144 pixels image is the actual unDemosaiced raw image data. The additional four 1424x1072 images are the separate GRGB planes from the CFA. If you just want to get the unDemosaiced raw image data without the 4 CFA planes you can turn off the "RGBG" checkbox in the RawImport dialog box.

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Joofa
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RFPhotography
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« Reply #24 on: March 27, 2012, 08:36:10 AM »
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You won't get a quadrupling of resolution.  No one has mentioned the Foveon sensor.  If memory serves, it shows about a 1/3 to 1/2 increase in detail resolution over Bayer sensors (e.g., a 12MP Foveon shows resolution equivalent to about 16 to 18MP Bayer sensor). 
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BartvanderWolf
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« Reply #25 on: March 27, 2012, 09:59:49 AM »
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You won't get a quadrupling of resolution.  No one has mentioned the Foveon sensor.  If memory serves, it shows about a 1/3 to 1/2 increase in detail resolution over Bayer sensors (e.g., a 12MP Foveon shows resolution equivalent to about 16 to 18MP Bayer sensor). 

Hi Bob,

The Sigma cameras with a Foveon sensor don't use an AA-filter. That's what causes the higher signal level in the highest spatial frequencies. Resolution is determined by the sampling density and the System MTF.

Cheers,
Bart
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RFPhotography
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« Reply #26 on: March 27, 2012, 10:06:34 AM »
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Very true, Bart!  And I should have said that too.  Apologies for the confusion and thanks for the clarification.
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hjulenissen
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« Reply #27 on: April 02, 2012, 04:52:06 AM »
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Hi Bob,

The Sigma cameras with a Foveon sensor don't use an AA-filter. That's what causes the higher signal level in the highest spatial frequencies. Resolution is determined by the sampling density and the System MTF.

Cheers,
Bart
If your scene contains lots of uncorrelated information in the color channels, a Foveon-style sensor should be able to resolve more luminance information than a similar pitched Bayer-style sensor, regardless of AA-filter. If your scene is truely wide-band "colorless", then Bayer should have no additional loss of spatial resolution.

I guess that it is possible to remove the CFA if you contact a company like maxmax, at least for some cameras? This should give a significant increase in luminance resolution on top of the increase coming from removing the aa-filter. This sounds similar to the idea that the thread starter had in mind?

-h
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BartvanderWolf
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« Reply #28 on: April 02, 2012, 06:03:54 AM »
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I guess that it is possible to remove the CFA if you contact a company like maxmax, at least for some cameras? This should give a significant increase in luminance resolution on top of the increase coming from removing the aa-filter. This sounds similar to the idea that the thread starter had in mind?

Hi h,

My experiments point to the conclusion that only a modest (<7%) increase in luminance resolution can be expected.

Cheers,
Bart
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hjulenissen
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« Reply #29 on: April 02, 2012, 06:22:42 AM »
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Hi h,

My experiments point to the conclusion that only a modest (<7%) increase in luminance resolution can be expected.

Cheers,
Bart
Am I right that your test is purely a computer simulation with equal modulation in all color channels?

If you had repeated the test with highly decorrelated color channels, or an extremely hot/cold spectral balanced scene, I suspect that you would have gotten a larger improvement.

-h
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BartvanderWolf
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« Reply #30 on: April 02, 2012, 07:30:46 AM »
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Am I right that your test is purely a computer simulation with equal modulation in all color channels?

Yes, that's correct. Luminance, and in particular that of edges, is the most important feature for human visual acuity. In addition to that, in nature it is common for chrominance information to fluctuate slower than Luminance. Just look at the channels of a Lab mode image to confirm that.

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If you had repeated the test with highly decorrelated color channels, or an extremely hot/cold spectral balanced scene, I suspect that you would have gotten a larger improvement.

Sure, but how relevant would such an unlikely combination of color and(!) brightness be? I know how to devise a worst case scenario, I even created a Blue/Red version of my test chart (see the links in the P.S. of the first message) that attempts to create such a situation for RGBG Bayer CFAs. But again, that would be looking for an improbable case because in nature we rarely see colors from opposite ends of the spectrum side-by-side, and even then they need to be of equal luminosity to cause a problem for CFA demosaicing.

Each of the R/G/B filtered sensels contributes (although weighted) to the luminance info that is used for the demosaicing process. That can be verified by looking at the R/G/B MTF curves of a demosaiced image, the curves align almost perfectly for luminance input. Here is a copy from output of a test on the Imatest website (look at the (RGB) read-out in Cy/Pxl ):

Cheers,
Bart
« Last Edit: April 02, 2012, 07:36:49 AM by BartvanderWolf » Logged
hjulenissen
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« Reply #31 on: April 02, 2012, 08:19:04 AM »
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Sure, but how relevant would such an unlikely combination of color and(!) brightness be?
And therein lies the success of the Bayer sensor, I guess: despite possible theoretical shortcomings, it tends to work well for the kind of images that we tend to care about.

It is nevertheless interesting to be aware of the conditions where Bayer is less ideal.

-h
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Christoph C. Feldhaim
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« Reply #32 on: April 02, 2012, 11:34:33 AM »
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The principle of a filtered sensel array is ingenious for a simple reason:
It allows to capture a great amount of information with a minimum of data junk.

We perceive resolution mainly through the luminance information, especially from the green channel.
This lies in the physiology of our visual system (retina rods are manly green sensitive).
The bayer patter exploits this and the result is a lot of information with a reasonably small file size at the RAW stage.

Just imagine all your raw files being three times as big, which would be the case if each sensel would record all color information, like the foveon sensor. The reasons above are also the reason why foveon is NOT equivalent to three times the resolution of a Bayer patterned sensor as has been discussed to death.

In the essence the filtered color arrays (not saying Bayer here, since Fuji has other patterns with the same effect) do a sort of information compression, which is similar to jpegs: reduce color information, but keep luminance information.

Thats just totally awesome.

~Chris
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