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Author Topic: Can someone provide a technical explanation of Fuji's EXR HR mode  (Read 633 times)
Dave Millier
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« on: May 08, 2014, 01:02:52 PM »
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Hi

I have a Fuji X10 compact that uses the EXR type technology.  Briefly, the EXR sensor is like 2 interleaved 6MP sensors.  You can set the camera to produce 6MP output in which case it blends the two files into a HDR image (this is different from standard HDR as it is single shot HDR).  If you shoot at 12MP output it produces a higher resolution file without the expanded dynamic range.  It is this latter mode I'm confused about.  

Using rawdigger to explore the files, I can see that the 12MP file actually contains 2 6MP frames, offset by 1 px.  I'd like to know what technique is used to combine these frames into a 12MP output file.  My tentative first guess is that it's a super-resolution type approach but someone has suggested that somehow they can use the sensor as if it were a regular 12MP sensor.  I find this suggestion difficult to understand and comparison of the 12MP files with the 6MP files suggests there is only a tiny improvement in detail.

Fuji are terrible at explaining the EXR beyond marketing handwaving.  Does anyone have a more convincing understanding they are prepared to share?

Cheers

Dave
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EricV
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« Reply #1 on: May 14, 2014, 09:22:08 PM »
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Each 6MP "frame" has a rectangular array of photosites, separated by 2X in both dimensions, where X is the nominal (full resolution) pixel spacing.  The frames are then interleaved, after shifting one frame relative to the other by 1X in both dimensions, so that the photosites of one array fit into the gaps between photosites in the other array.  The final full resolution sensor has 12MP in a non-rectangular array, sort of like a brick wall with staggered rows of square bricks.  Does that make sense?  It is similar to super-resolution, like what you would get if you had a single 6MP sensor and combined two images, shifting the sensor by 1/2 pixel in both dimensions between images.  Except it is not really super resolution, because there are really 12MP photosites.

The HDR aspect requires operating the two frames at very different sensitivity, apparently by electronically controlling the exposure time.  Dark areas in the final image are constructed from pixels in the frame which had full exposure time (for low noise), while bright areas are constructed from pixels in the frame which had reduced exposure time (to prevent saturation).  Using the pixels this way of course prevents using them in the full resolution mode, so you get a 6MP HDR image.

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