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Old Feb 15, 2010, 12:12 AM   #1
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Default HDR or not?

I've found the various discussions about HDR and pseudo-HDR quite interesting. I have a couple of observations about it all.

First, even if you have 5 different exposures, some pictures don't get better in Photomatix. Friday I was out snowshoeing, taking snow pictures and also some pictures that were for a lens comparison. I was using auto bracketing for two reasons - some of the scenes I wasn't sure about the exposure so wanted to bracket. Some I wanted to shoot for HDR. I didn't bother turning auto bracket off when I was shooting tree bark for the comparison shots. So I have this 5 shot series, shot hand-held:



There's very little dynamic range in the scene. Here's the middle exposure - there's no need for HDR, it's fine the way it is:



I ran the 5 exposures through Photomatix, just to see what the program would come up with. It looks almost exactly like the middle exposure, just a bit softer. The middle exposure is slightly better in the sharpness. There's a bit of difference in color, but that would be easy to match in Photoshop.



Photomatix doesn't add anything to this scene - HDR isn't needed with it.

Then I took some series of a scene that perhaps could use additional dynamic range - to get the rocks properly exposed would blow out the snow. The middle exposure shows that the meter was too influenced by the snow - it's underexposed.



Being underexposed isn't such a bad thing with this picture - a little adjusting in Lightroom gave me this:

.

This is about as light as I could go with a global change without blowing out the snow.

For the pixelpeepers - here's a 100% crop showing that there's still some detail in the snow. One could probably do some layers work to lighten the rocks a bit more while leaving the snow alone, but I would rather not have to do layer masks if I can avoid it (get frustrated easily).



Here's the Photomatix version of the picture, made up from another 5 exposure auto bracketed series. The snow on the left side isn't perfect (too grey IMHO) but the rest of it worked out well enough.



Another 100% crop - shows more detail in the snow, might do better with a bit levels adjustment.



Finally, with all the talk about how blending layers in photoshop was quicker, it reminded me that there's a rather manual way of doing HDR in an old, relatively low-tech way. Basically you take two layers, dark over light. Add a layer mask, copy the lighter layer and paste it on the layer mask. Merge the two layers and add another layer - do the same thing. I only used 3 different exposures - I thought there wasn't enough useful information in the lightest and darkest frames - this method would probably work better with this scene if I had used less difference between frames, then I could have useful information in all the frames. I've used this method successfully before, but there's no way to make any adjustments if things go wrong. And I wasn't sure that CS4's align layers feature would be up to matching this hand-held 5 frame series (it was, worked well). The snow looks better in this frame.



Another 100% crop:



There's more detail in the snow than the single file. Photomatix doesn't like white objects, it wants to make them grey (reminds me of the meter on the camera). So in this case, the mechanical, relatively low-tech way of doing HDR worked better than the higher tech Photomatix. And it's a reminder that there's more than one way of going about things, and that what works in one situation might not work the next time.
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Old Feb 15, 2010, 1:06 AM   #2
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If you want to drive in a nail a hammer is the tool. If you want to screw in a screw use a screwdriver. If your photo needs to have some details in the highlights and shadows then go HDR. Every tool has its purpose and using a screwdriver to bang in a nail is not the way to go. Looking at the scene you are shooting and using common sense will tell you whether to shoot for HDR or not. Bright sun and shadows is a good place. The pic of tree bark doesnt need much dynamic range. Im not sure what point you are trying to make here about HDR. Whether to use it or not or go a different route to achieve the final results. Photomatix, for example, has so many sliders and choices to make, your end results can be anything from excellent to pitiful. Its all in the hands of the operator.
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Old Feb 15, 2010, 1:41 AM   #3
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The snow pic should bring out any benefits of HDR but I can't see any. The lichen on the rock looks better in the single image pic and I wouldn't be surprised that more detail could be brought out in the snow, with a bit of playing around.
Could you post the RAW please ?
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Old Feb 15, 2010, 3:13 AM   #4
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I think you're right about the bark but on the snow I think it's Photomatix rather than the HDR principle that's the problem. The middle exposure alone does contain enough to get a lot more detail in the snow.

[EDIT] although I'd say that you need to go softly with it. I find HDR tends to make everything look shinier and more glassy which in this case changes the characteristics of the snow and makes it look more like icy snow than fluffy snow.

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Old Feb 15, 2010, 10:10 AM   #5
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My point is exactly Bynx's point - you use what's appropriate for a scene. HDR is not a magic bullet to fix all shots.

I've been seeing some people ask about HDR and then show examples of pictures where they've used it on scenes where the middle exposure was flat, but didn't have anything that was beyond the dynamic range of the sensor. My tree example was very extreme, but it shows that Photomatix won't do much for those types of scenes, even if you do exposure bracket them.

The snow picture was interesting to me - I was surprised that I could lighten the underexposed rock as much as I did without introducing a fair amount of noise, but the rocks are still darker than I would have liked. I probably could have gotten them the way I wanted by using layers and layer masks in CS4, but didn't want to mess with all that.

Martin's comment about the grey snow is being caused by Photomatix, not the process, is what I was trying to point out - that particular program doesn't like white things (I've seen other people posting pictures of interiors with windows where you can see the same thing). It's great for other things (as I think I've shown with some of my other pictures posted around here).

The manual layer method in Photoshop (you can use it in just about any version of Photoshop that supports layer masks) worked well with this particular picture, I was happier with this version than I was with the others. However, I tried it on another snow shot and it didn't work at all. When I tried to add the layer that didn't have the snow blown out on it, the whole picture went too dark. Photomatix did the best for that picture.

I tried to use dphdr, but I don't know enough about the program to know what I did wrong - the results I got were dreadful but I'm sure that was my ignorance in not knowing how to set it up right, rather than the program not being able to handle the scene.

Martin - It was definitely icy snow, not fluffy snow in reality, and I was happy that the HDR versions picked that up, rather than a fluffy white mass. Its more fun to snowshoe on a fluffy white mass, but what I usually see is wet snow re-frozen so that it's more like a snow-cone than the light, fluffy stuff.
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Old Feb 15, 2010, 10:12 AM   #6
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Oddly enough in the first series of shots I posted in my "speculations" thread, Photomatrix turned the whited out sky into a grayed out sky. I guess the program thought it was doing me a favor... It's probably some sort of default setting when the program encounters blown highlights... In the Photoshop Layers HDR picture I added at the end of that thread, the Photoshop version handled highlights better than the Photomatrix (not posted) version. Dave Dave
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Old Feb 15, 2010, 12:22 PM   #7
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As I understand it, and correct me if Im wrong. But each exposed photo is a layer so in a 3 shot HDR there would be three layers and the pixels would line up directly over each other. Photomatix goes through each layer of pixels and selects the best pixel, perhaps an average of the 3. This illustration I hope is understandable. Ignore the green color. It was used to separate the white from its background. The circles represent the individual pixels from an image. The gist of it is that something black will remain black. While if it just dark then it can be lightened slightly and if its white it can be darkened slightly. If its pure white it will (or should) remain white.
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Old Feb 15, 2010, 1:30 PM   #8
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I don't think that's quite right. I think it's like this: You have say 3 12-bit RAW files. they are all clipped at one or both ends (shadows or highlights). You load them into a program such as Photomatix which stiches them together to create what a 24-bit or more sensor could have captured.



The next bit is harder to explain but basically you need to work out for every pixel whether it's needs to be lightened or darkened. The way to do that is to look at the surroundings. If everything nearby is dark then the whole area is probably underexposed and needs to be lightened. The tricky part is how you define 'surroundings' especially at edges and which is why halos occur if you get it wrong.

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Old Feb 15, 2010, 2:48 PM   #9
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A very interesting subject. I do not think it is as simple as Bynx points out, but it someway up that street. I think that there is much more mathematical calcualtions involved. As Martin points out it must take into considerations the neighbouring colours because not all whites get dirty. It does use some sort of mathematical matrix, that varies from program to program, because there are some places in the Photomatrix HDR where the snow is overexposed whilst in the "manual" HDR it is not.

Basically I think one must think in mathematical terms to find out how Photomatrix, and other HDR programs, process the pictures they are fed.
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Old Feb 15, 2010, 3:07 PM   #10
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Martins use of histogram pictorials is, to me, a little more involved than the simplistic way I was trying to explain what I think. But as I say, its only as I understand it and that might be all wrong. Martin has probably a better grasp than I since he has made a program similar to the other HDRs. I can see one problem though. While I show dots and their shading values what the HDR program would see would be numbers. Its all about number crunching. I hope when this thread progresses I can actually understand properly what goes on when Photomatix et all does their magic.

After looking more closely at Martins histograms they make sense but not on a layer by layer pixel by pixel as I have produced. His shows what needs to be done. Mine shows the final results. Neither are right or wrong, just what you can get your head around. Ive always had problems understanding fully histograms. I mean you cant manipulate them as far as I know.

Last edited by Bynx; Feb 15, 2010 at 3:12 PM.
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