Compiling photos for HDR

[polarmagnus]

Hope I've put this in the right category.


I always take 'bracketed' shots in the P mode and let it choose the aperture and ISO.

When I load them in the Merge to HDR in Photoshop CS3, the photo always seems flat.

Should I be using the same ISO and aperture for all the images of different exposures?

[Stargate 01]

Hi polarmagnus, the quick answer is yes you should use the same iso and apeture for all your exposures. Try switching to Apeture Priority then take note of all the settings and then switch to Manual mode and dial in the settings that you recorded and that should give you a good starting point.

Hope this helps........

[GeoffWessex]

Stargate01 is right to say Aperture Priority (Av), which won't try to change ISO (or aperture) to compensate for the differences.... it will just use different shutter speeds. Manual mode should be unnecessary unless you don't have the bracket facility.

The problem with P or Program mode is that it has the ability to alter ISO, Aperture and Shutter Speed, in trying to come up with a 'good' exposure for every shot. You don't want that - you want some underexposed, some overexposed and one 'medium'.

Your 450D has the ability to bracket shots, but only 3 shots, 2 stops apart. That's a nominal 4 stops in Exposure Values (+2, 0 and -2). Not really ideal for HDR, which often needs an 8-stop EV range or more. You could widen your range by adding Exposure Compensation - for example, if you took your bracketed three shots with +2 stops of compensation applied, then took three shots with -2 stops of compensation applied (keeping the camera fixed in position for both sets, of course) you get a full spread of exposures.

Let's say the 'medium' exposure gave you 1/500th at your chosen aperture, without Exposure Compensation you'd get shots at 1/125th, 1/500th and 1/2000th.

If you apply +2 stops of compensation, you'd get 1/125th as your 'medium' value and get shots at 1/30th, 1/125th and 1/500th;
If you apply -2 stops of compensation (so 1/2000th becomes the medium) you'd get shots at 1/500th (again), 1/2000th and 1/8000th. You'd then achieve an exposure range of 1/30th to 1/8000th.... a total of 8 stops of EV range. You'd end up with six shots - two of which would be identical, at 1/500th.

(Sorry, sometimes you just need to get a pencil and paper out!)

[polarmagnus]

I think you lost me on your fourth paragraph lol

I took 100+ bracketed shots this morning using two daylight bulbs, and ran a couple of photos through Photoshop and they didn't turn out as well as I would like them to.

I think really I need Photomatix to obtain a better HDR shot.

[chris-p]

Goeff is right - you need to increase your exposure range and your tonal range. Software is not your problem.

There are a fwe golden rules for HDR. First off, never change the aperture. It affects sharpness and depth of field and that will make your HDR images look soft and they'll lack detail.
Secondly, never alter the ISO as you'll introduce noise and minor A/D conversion artefacts which will affect microcontrast and weaken colour.

Auto bracketing is rarely (if ever) suitable for HDR. Most people's HDRs look flat because you're only ever getting 3 exposures and they're usually not far enough apart. If you want to get HDR photos to look good you need to use either aperture priority and exposure compensate or manual mode and just adjust the shutter speed.

Put it this way: +2, 0 and -2 is never very good. +2, +1, 0, -1 and -2 is far better. You'll get more tonal range, better contrast, more detail and better colour.

On top of that, you need to actually work out if your -2 is dark enough or your +2 is bright enough. For the best results the darkest (most underexposed) shot needs to be about 2 stops under the highlight clipping and the brightest (most overexposed) shot needs to be 1 stop over any shadow clipping. For an average landscape scene (and I've shot a lot of HDR) that is usually something like a +4 down to a -6 or-7 with each individual stop in between (+5, +4, +3, +2, +1, 0, -1, -2, -3, -4, -5, -6, -7)

Any software can only work with the image files, and their associated luminance values, that you give it. If you don't give your software enough data you won't get good results.

[MattUK]

Interesting reading, though I use auto-bracketing with a 2 stop EV range (+2, 0, -2) and I'm very happy with my HDRs in my gallery...

[Cathus]

autobracketing is fine, especially if you have a camera with 5 or 7 shots' worth of autobracketing, though I tend to just put the camera in manual, wind the shutter down to a few stops under what the camera recommends & then take a shot, wind the wheel 3 clicks (1 stop), take a shot, wind the shutter 3 clicks, take a shot, until I have taken a few stops over the recomended setting.

Chris, you have a habit of using language & explanations which go way above the average understanding.

"minor A/D conversion artefacts which affect microcontrast" Given the original question asked, is it likely that sentence will make much sense to the average forum goer? (it doesn't to me )

[GeoffWessex]

Yes, my camera has a range of 5 shots for auto-bracketing. I also explained (having looked at the OP's camera specs which showed only a 3-shot bracket capability) that he may need to run a bracket of 3 shots from a 'plus' exposure compensation and another 3 from a 'minus' exposure compensation, so that a good range of exposures is collected.

I was reading an article last month (in a UK magazine) by Michael Freeman, and he said that any less than a 2-stop difference in exposure is fairly pointless. I tend to agree.... I used to bracket five shots 1 stop apart - and those +1 and -1 shots weren't really helping things, and in fact slowing down processing time.

[polarmagnus]

Geoff
How do you find out how to take more bracketing shots than the camera specs say it can do?

[MattUK]

You can do it manually. Set the aperture you want in manual mode, and take a meter reading. Then manually take x amount of shots with a shutter speed above and below the perfect meter reading..