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Author Topic: HDR test  (Read 6185 times)

Fine_Art

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HDR test
« on: June 01, 2014, 07:11:17 pm »

I am a HDR newb. This was 3 .7ev bracketed shots out of a big pano.
I did the raw conversion into 32bit floating point in images plus. Screengrab to MS paint.
Snow tones seem ok? Darks Ok? Nothing looks nasty grunge to my eye. Opinions?
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Fine_Art

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Re: HDR test
« Reply #1 on: June 01, 2014, 07:20:27 pm »

Here are the 3 frames in linear 32 bit FP for interest in discussion. Screenshot cropped.

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Slobodan Blagojevic

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Re: HDR test
« Reply #2 on: June 01, 2014, 07:46:13 pm »

It does not look like a HDR because the end result doesn't appear to be any different than a single capture?

Fine_Art

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Re: HDR test
« Reply #3 on: June 01, 2014, 10:02:23 pm »

It might not look vastly different from the brightest  +.7 in linear, it is still plus about 1ev dynamic range over the D600 regular. The brightest is blown out in the snow even before gamma. I am using the darks from the brightest shot with a small gamma curve, not the typical 2.2. The snow is from the darkest bracket with gamma near 2.2 taking it close to 65535 in 16 bit.
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stamper

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Re: HDR test
« Reply #4 on: June 02, 2014, 03:50:40 am »

When you shot the scene did you think it was a high contrast scene that justified the need for HDR? I have the D600 and in my limited knowledge of using Rawdigger then the D600 has about two and two thirds of headroom exposure before over exposure becomes a problem. Your image looks a little flat.

Fine_Art

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Re: HDR test
« Reply #5 on: June 02, 2014, 11:26:25 am »

When you shot the scene did you think it was a high contrast scene that justified the need for HDR? I have the D600 and in my limited knowledge of using Rawdigger then the D600 has about two and two thirds of headroom exposure before over exposure becomes a problem. Your image looks a little flat.

I have no idea what you mean. To me blown is blown. If something is colored it might blow on only one channel so software can "reconstruct" to some level of acceptability. Sunlit snow is going to blow out fast. Yes, I saw it as a HDR scene for the mixed clouds with sun. I wanted a shot with clear control of the sunlit snow, I wanted a shot with detail in the shaded trees.

How the software decides what to map where, I have no idea. I know I fed it 3 images .7 ev apart. It gave me one output image to work with. I decided to output as 32bit FP .fit so I could manipulate it with lots of tones.

Maybe the trees look flat, I am undecided on the proper lightness for them. They need to be lighter without turning the rest of the image flat. I am trying to do that without using masks on the file. That needs more work.
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bill t.

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Re: HDR test
« Reply #6 on: June 02, 2014, 06:46:47 pm »

I generally agree that this is not a good HDR candidate scene based on brightness.  But OTOH, sometimes HDR on realtively low brightness scenes can give you a richer looking image and lower noise.  Sometimes.

I notice that all your exposures are much too dark for a good HDR set.  Your "middle" exposure is more like what one would want for the darkest exposure, and there is not an appropriate "bright" exposure that includes details in the darkest areas of the trees.  Basically, your HDR set is overall about 2 stops underexposed.
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Slobodan Blagojevic

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Re: HDR test
« Reply #7 on: June 02, 2014, 07:21:33 pm »

Doing bracketing at ⅔ f-stop intervals does not make much sense for HDR, as almost any modern camera, and certainly D600, can easily cover such a dynamic range in a single shot.

Fine_Art

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Re: HDR test
« Reply #8 on: June 02, 2014, 07:56:49 pm »

Doing bracketing at ⅔ f-stop intervals does not make much sense for HDR, as almost any modern camera, and certainly D600, can easily cover such a dynamic range in a single shot.

You are right. I went back to have a look at the files in Nikon's ViewNX. The darkest file does fit everything in with a ETTR.
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Fine_Art

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Re: HDR test
« Reply #9 on: June 02, 2014, 07:59:36 pm »

I generally agree that this is not a good HDR candidate scene based on brightness.  But OTOH, sometimes HDR on realtively low brightness scenes can give you a richer looking image and lower noise.  Sometimes.

I notice that all your exposures are much too dark for a good HDR set.  Your "middle" exposure is more like what one would want for the darkest exposure, and there is not an appropriate "bright" exposure that includes details in the darkest areas of the trees.  Basically, your HDR set is overall about 2 stops underexposed.

I may have confused the issue showing the linear data. This is the brightest file untouched in Nikon's ViewNX It is blown by about 1.3 stops. The darkest file is ETTR.
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Fine_Art

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Re: HDR test
« Reply #10 on: June 02, 2014, 08:04:17 pm »

This is the darkest file. Sorry for the confusion, people are not used to seeing linear, that is my posting error.
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stamper

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Re: HDR test
« Reply #11 on: June 03, 2014, 05:01:34 am »

I have no idea what you mean. To me blown is blown. If something is colored it might blow on only one channel so software can "reconstruct" to some level of acceptability.

Download RawDigger and you can judge more accurately if something is blown. You can't rely on the histogram on your camera or in LR or PS or a similar program.

http://www.rawdigger.com/

Some Guy

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Re: HDR test
« Reply #12 on: June 03, 2014, 10:42:13 am »

Shadow detail in the trees - or is it a lake reflection below the mountain? - is much too dark for an HDR, imho.  A good HDR should show more shadow and/or highlight detail than presented.

Only 0.7 stop is too little.  Bump that up to maybe +/-1 or even two stops for HDR as your Nikon has ADL (if you use their software to read it) to cover the smaller stuff.  If something is too dark or two light, 2 stops might pull that back into a workable range at the expense of burying the other end in the wall of the histogram.  The HDR software will fix that matter once it combines them all.

SG
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Fine_Art

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Re: HDR test
« Reply #13 on: June 03, 2014, 02:55:09 pm »

2nd try. The trees look better. It's starting to skirt the edges of becoming a caricature of the original scene. My own tendency is to tone the contrast back a bit from here.
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Tim Lookingbill

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Re: HDR test
« Reply #14 on: June 03, 2014, 05:18:56 pm »

Your blackest black in foreground brush detail is around 20RGB in the green channel. Is that shot taken at night? Morning?

Try a notch curve in the area of 20RGB luminance to add definition.

Or find a slider adjust in your software that linearly shifts the entire image to the left viewed in the histogram (gamma encoded readouts NOT LINEAR) to establish absolute black and then apply a huge shepherd's hook shaped curve which most Raw converters already apply so you don't have to deal with editing such dark images.

You're having to keep going back and editing the image and still having it look dark at least as it shows on my calibrated display indicates you're not using the entire dynamic range captured and/or your software isn't helping you very well. I've taken far more dark, high contrast images than yours and normalized so it isn't that dark. Whatever software you're using is making it harder for you to achieve this. 
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Fine_Art

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Re: HDR test
« Reply #15 on: June 03, 2014, 09:59:25 pm »

One of my reasons for trying the HDR technique was the 'zero noise' process created here by our Spanish member, Guillermo. Lower noise, supersampled resolution, more tones in the data, everything seems to point to using multi-shot techniques. If I look at the tree line in the image that fits everything, the trees are limited in definition relative to the brightest shot. The brightest shot has the shape of branches. The darkest is a soft outline. I'm sure I was using MLU with a cable release so it was either a wind gust or the raw processor does a far better job with higher value data. I have to decide if it is worth the process of HDRing all the shots, getting them to a certain look, the stitching them. Its about an 8x3 pano so it's a lot of mucking around in software.

Is it worth getting into the habit of always using a multishot process for static subjects?

Image added.
« Last Edit: June 03, 2014, 10:05:25 pm by Fine_Art »
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Tim Lookingbill

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Re: HDR test
« Reply #16 on: June 04, 2014, 12:49:57 am »

Its about an 8x3 pano so it's a lot of mucking around in software.

Is it worth getting into the habit of always using a multishot process for static subjects?

Image added.

I don't have the patience nor do I ever find a need to shoot scenes that require stacked exposures. Your scene of the mountains can be done with one exposure.

Guillermo's HDR process is for real HDR scenes that attempt to retain detail in both low lit (about 2000 lumens) architectural interiors with a lot of smooth surfaces in the shadows of furniture that perceptually amplify noise while at the same time retain outdoor day lit (about 10K lumens) scenes in open windows.

Your landscape is lit by a giant ball of fire in the sky which provides quite a bit of full spectrum photons even in shadows for your sensor where very little noise is going to be present if not hidden within the texture of trees and grassy fields. You have a more advanced camera especially for low noise than my 2006 Pentax K100D DSLR, so I don't see why you have to go through so much trouble with a landscape scene that's not technically HDR.
« Last Edit: June 04, 2014, 12:51:58 am by Tim Lookingbill »
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PhotoEcosse

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Re: HDR test
« Reply #17 on: June 04, 2014, 09:17:46 am »

With the much improved dynamic range of modern digital sensors (14.3 EV in the case of my D800 and D800E) I find that the need/benefit of HDR only emerges when the DR of the scene is such that I need to take 7 or 9 exposures at 1 EV intervals to get a good final image. (Actually, using Nik's HDR Efex Pro, I only use the odd-numbered images at 2EV intervals, but the auto-bracketing on my particular cameras only allow up to 1EV intervals !! )
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Fine_Art

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Re: HDR test
« Reply #18 on: June 04, 2014, 10:34:39 am »

I don't have the patience nor do I ever find a need to shoot scenes that require stacked exposures. Your scene of the mountains can be done with one exposure.

Guillermo's HDR process is for real HDR scenes that attempt to retain detail in both low lit (about 2000 lumens) architectural interiors with a lot of smooth surfaces in the shadows of furniture that perceptually amplify noise while at the same time retain outdoor day lit (about 10K lumens) scenes in open windows.

Your landscape is lit by a giant ball of fire in the sky which provides quite a bit of full spectrum photons even in shadows for your sensor where very little noise is going to be present if not hidden within the texture of trees and grassy fields. You have a more advanced camera especially for low noise than my 2006 Pentax K100D DSLR, so I don't see why you have to go through so much trouble with a landscape scene that's not technically HDR.

Your post makes sense in theory. I still have to deal with the experimental evidence of more detail in the shadows of the overexposed shot. Yes, one shot will do. More data does seem to capture it better. I also have quite a bit of experience using the multishot ISO NR built in to the Sony camera. It takes several fast shots (no mirror flapping) putting them together into a single jpg output. in many outdoor scenes it was the only way to get all the data in to one shot.
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kirkt

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Re: HDR test
« Reply #19 on: June 04, 2014, 11:37:09 am »

Sometimes, all you need is a few extra stops in one end of the exposure to create the image you would like, with the room to make the edits you like.  The two basic routes are exposure fusion and HDR merge, with programs like ZeroNoise being a hybrid of the two.  More recently, this hybrid method has been implemented such that one may output a "noise free" DNG, making this data amenable to a raw workflow (see LumariverHDR, for example).  I know that Guillermo's approach included plans to write the output from ZeroNoise to DNG - LumariverHDR picks up where Guilllermo's approach left off.  In cases where you only need a few extra stops of good data, you can get away with 2 or 3 images at +/- 2EV for this hybrid method.

Another approach that is really interesting but requires a little more of a convoluted workflow and understanding of the limits of the output (and a Canon camera) is the Magic Lantern DualISO module for supported Canon cameras.  The supported Canon sensors have a design that the ML folks have exploited to read, simultaneously to a single raw file, alternating stripes (every 2 sensor lines) of the sensor at two different ISOs.  This permits one to expose for one end of the scene and then use the DualISO module to acquire the other end of the scene simultaneously.  For example, you can expose for the highlights in a scene (even ETTR exposure) at ISO 200 and set up the DualISO module to also acquire half of the sensor at ISO 1600.  This results in better exposure of the shadows, with less noise.  The single resulting raw file is then processed with a small application (cr2hdr) that combines the striped data into a single DNG.  The method has its downsides (resolution, moirĂ© can result) but is a very effective way to expand the useable dynamic range of your sensor AND capture moving subjects that, typically, produce alignment and ghosting issues in traditional HDR techniques.

kirk

« Last Edit: June 04, 2014, 11:56:12 am by kirkt »
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