HDR Bracketing: One or two stops?

[rpcrowe]

I like fairly natural looking HDR imagery. I also prefer to shoot my HDR images using three bracketed exposures since my Canon DSLR cameras can automatically bracket three shots when I am shooting in the burst mode.

I realize that five images may give a better HDR composite but, since my coordination is not that great (I have problems walking and chewing gum at the same time!); the automation of shooting three bracketed exposures in burst mode is probably best for me.

The big decision is whether to bracket one stop or two stops. Is it carved in granite that the HDR image should be bracketed either one or two stops or is the amount of bracketing dependent on the subject matter? If the exposure is subject matter dependent, how would I determine how many stops to bracket?

Additionally, does it matter in which sequence I shoot my bracketed exposures? As an example, the default setting sequence for Auto Exposure Bracketing on my 40D is: standard exposure - increased exposure - decreased exposure. However, if I wish, I can change the sequencing. Is there any reason to switch from the default setting?

Additionally, if I shot the bracketed exposure in the default sequence; would it matter in which sequence I choose these images for combining into an HDR composite?

Thank you!

[The Blue Boy]

I shot this using the 2 stop bracketing technique with my Nikon D80. I'm no expert and this was one of my first ventures into HDR.

Mark

[David]

Hi rpcrowe I don't think there is any hard and fast rule about how many stops you use to bracket the images, but normally people use +/- 2 stops to get a reasonable dynamic range. Others claim an even wider range, although personally using a Canon 40D I find the 2 stop range sufficient. As to the number of shots, I have found that taking 5 images at +/-1 and +/-2 stops does lead to a better(?) resulting image. The problem is that you cannot take the 5 shots automatically. Consequently, if there is any movement in your subject or any variation in light quality or quantity any advantage of 5 shots as opposed to three is lost.

As far as I know, the order in which the bracketing is carried out should not matter if conditions remain the same during the three exposures. Normally, software such as qtpfsgui or Photomatix can assess the exposures in terms of EV and combines them appropriately. Software from FDRTools allows you to alter the sequence of images, but, more importantly, you can alter the weighting of each image prior to tone-mapping. Also, this software appears to give more natural looking images than some other algorithms.

The key is to experiment. Have fun.

David

[McQ]

There's of course no set rules, but generally speaking, if you can capture the entire dynamic range with +/- 1 stop, then shooting separate images in HDR is probably not essential in the first place. You could likely take a single photo in RAW and develop it three times with 0,+/-1 stop, for example, without hugely different results. Using +/- 2 stops will give you less noise in the shadows and will allow the HDR software to slightly better estimate your camera's tonal response curve. Similarly, a more accurate tonal response curve is the main reason why people advocate using 5 shots over 3. As David pointed out, it can definitely lead to a better, more accurate HDR image.

[Vandenberg]

i use 3 stops, and seems to work great

[tonyjr]

HDR +HIGH DYNAMIC RANGE . The more stops 2 as opposed to one , the more high lights on one end and more shadows on other end .
I am just starting to play with this so I may have my head up my ---- . If so I hope someone explains it better .

[_GUI_]

The more shots the better HDR quality is a myth. If we distinguish 2 stages in the HDR process:
1. Capturing all the scene's DR (CAPTURE)
2. Processing the RAW files obtained to get the final image (TONE MAPPING)

In the first stage the only rule is to capture all the DR of the scene, and that simply means capturing the highlights without blowing them, and the overall image sufficiently free of noise.

With just 2 shots 4 stops apart (yes, 4EV) of carefully chosen exposure in a modest Canon 350D you can capture with an outstanding quality scenes of up to 12 f-stops of real DR. An additional middle shot would improve noise in the middle tones, but it is not essential.
Any higher number of shots will never improve the captured DR as long as the difference between the most and least exposed shots remains 4 stops or less.

So answering the question "1 or 2 stops bracketing", if 4 stops is truly possible, I would never do 1 stop bracketing {-1,0,1}, and would prefer {-2,0,2} instead. I cannot think of a single case where {-1,0,1} can produce a better result than {-2,0,2}. On the other side {-2,0,2} will outperform the result of {-1,0,1} in many cases of high DR or simply not optimum exposure values chosen.

Once I saw a guy showing a picture made of 19 shots at different exposures 1/3EV apart. That is absolutely mad and non-optimum since it will probably deteriorate the sharpness of the final image if the 19 shots are not milimetrically aligned.

This scene was captured with just [COLOR="red"]2 shots, 4 stops apart, is entirely free of noise, and had [COLOR="red"]12 f-stops of real dynamic range:




The tone mapping was made straight into ACR (using the tone curve basically) and allowed to achieve the goal of getting a reallistic appearance.

Unfortunately there is a lot of confusion about what HDR is, and most people experimenting with HDR looking at that image will claim: "but that is not HDR!". It IS HDR. It is a high DR scene, all the information was captured, and it was tone mapped and presented to the observer with a natural looking, like what he would have seen being there.

What all those people think of when talking about HDR has little or no link to dynamic range, but to the unreallistic appearance through HDR automated tone mapping processings they are looking for, like those obtained with Photomatix for example.

An another myth is that to store a high DR scene we need a floatint point format such as radiance. A 16-bit integer linearly encoded image can store with no problem up to 12 f-stops of DR, more than enough for 99% of high DR situations in real life. And if the encoding is not linear (e.g. a gamma 2.2 curve is applied) the real encoded DR can be much higher as long as you shot the needed shots at the proper EV intervals to capture it.

[Colin Southern]

For what it's worth, the academy award winning guru in one of my HDR books suggests that 2 stops is usually about right interval - BUT - you none-the-less need to take as many shots as is needed to cover the entire dynamic range of the scene.

If you're only going to take 3 shots then a 2 stop bracket may or may not be enough - it depends totally on the scene.

Cheers

[babylhot27]

i am using nikon d60. i tried to look for bracketing but i can't find it. just want to try learning and making HDR images. how to do it using my dslr? please help...

[Colin Southern]

I just had a quick search through an online manual for the D60 and (surprisingly) couldn't find any references to bracketing - so perhaps it doesn't have that feature? (I'm a Canon shooter and don't know the Nikon range very well, so I could be wrong).

It shouldn't make much difference for landscape type shots though - I imagine that you could easily dial in a couple of stops of exposure compensation (after taking the initial shot) - or use the camera in manual mode where you can (manually) shoot as many bracketed shots as you like.

Cheers