HDR and HHT

Started Jan 24, 2012 | Discussions thread
blue_skies
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Re: HDR and HHT
In reply to AlexG47, Jan 24, 2012

You are close - see the links above.

The HDR takes three images: correct exposure, overexposed and underexposed, and it then 'flips' the logic (and you can control by how much):

  • From the overexposed image it finds the 'dark' areas (removes lowlights)

  • From the underexposed image it finds the 'light' areas (removes highlights)

  • All other areas come from the correct exposed image

Be careful with HDR with (fast) moving subjects - they can 'disappear'.

HHT, as I understand it, simply takes six underexposed pictures in rapid succession, and adds the data together (aligns each picture and sums it up). This removes camera shake, and lets you indeed take a 1/60th equivalent picture at a 1/10th effective shutter speed (6 times 1/60th). It works best on static objects. It removes the camera shake.

AMB (Anti Motion Blur) is similar to HHT, but it averages the six pictures (it also aligns them). It doesn't give you a longer shutter time, but it removes movement (subject blur) in the averaging process. The idea is that e.g. you can use a 1/20th exposure time, with an OSS lens, but your subject does not want to sit perfectly still. The six shot exposure removes as many subject movement based blur as possible.

In short:

  • HDR - reduces blowouts (hi/low) by using multi-exposure

  • HHT - reduces camera shake for 'virtual' extended shutter times

  • AMB - reduces subject blur for sharper images with longish shutter times

HDR work well in daylight, and can be compensated for in PP
HHT is best for lowlight
AMB has some mixed results, partially because OSS is also effective on its own

Above is my basic understanding, but I can be wrong too

AlexG47 wrote:

I haven't received my NEX7 yet, but I have bought Sony HX5V to understand how HDR and HHT work.
This is my knowledge:
HDR
Assume the total exposure time is 100 ms (miliseconds) or 1/10 sec.

After 1 ms (1/1000s) camera saves the first image (sky, clouds and bride gown), and keeps aperture opened!
After 10 ms (1/100s) camera saves faces and keeps aperture opened.
After 100ms (1/10s) camera saves black groom suit and finaly closes aperture.
Then camera recalculates three signals into one and creates a single image.

Of course this image is too soft, but really it is not an image - it is the overwhelming light information.

Use Post Processing and create perfect, noise free image. Sky, clouds and black suit wrinkles will be perfectly visible (without polarized filter)
If you are too lazy and don't want to correct image - forget about HDR.

HHT
Same stuff - 100 ms.
After 17 ms (1/60 sec) camera saves image 1 and keeps aperture opened!
17…34 ms - image 2
34…50 ms - image 3
50…67 ms - image 4
67…83 ms - image 5
83…100 ms - image 6 and finaly closes aperture.

Then camera perfectly stitches 6 images into one and finally you have 1/10 sec exposure image with sharpness similar 1/60 sec.

HHT MAKES SENSOR 6 TIMES BIGGER (NEX7 = Mamiya).
You can watch your HHT image without PP.

P.S.
Please don't think every click is related to every shot, is not.

If you don't trust - keep camera stable within two clicks and suddenly turn it away.

After movement you will hear additional 4 clicks, but the image (6 pictures) will be perfectly sharp.

You should hold camera stable just within 0.5 sec (for safety), even thou you hear 6 clicks within 2 or even 3 seconds.

Please let me know if I'm wrong. My mistake is my education.

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Cheers,
Henry

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