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Exposing for Photomatix?


HowardA 13 231
15 Feb 2007 2:18PM
Hi all. Had my first go with the trial version of Photomatix yesterday (after a quick dash into Chester cathedral). Love it and will certainly buy the licence. I used average metering and bracketed 2 stops either way. However, some of the lighting was still blown out after running the tone-mapping. Would you recommend spot metering on the lightest areas for the first (average) exposure?
Very excited at the prospect of this and await receipt of the 10-20mm lens to do the cathedral some justice!
Any advice on this one? Following my previous thread on interior lighting for brochure shots I can definitely see that multi-exposures and tone-mapping is a good solution to the problem - thanks to those of you who commented on that query.
Cheers, Howard
keithh 16 25.7k 33 Wallis And Futuna
15 Feb 2007 2:37PM
You'll find as many ways of producing an HDR/mapped image as there are people trying it at the moment - but the more experienced users, and by that I mean those who have been using it for several years, stand by a series of images with a 2 stop difference between each.

Beginning with a metered average exposure and then by taking whatever exposures you need to capture the whole range of shot you're after.

It's worth checking your shots with the histogram as you scroll through as ideally what you are looking for is a very similar technique to taking panoramics...ie...enough overlap. What you want in each shot is coverage outside of the shot before and after it but with enough overlap of the range in each.

Outside of your average shot, your two most important ones are the final over-exposed and your final under-exposed. Each of them should contain some useful information and not just be black/burn out captures.
HowardA 13 231
15 Feb 2007 2:47PM
Thanks Keith.
I had used the auto-bracketing on the D50 which gives me three shots in total. It generally seemed to be fine for the architectural features but was thrown by some windows at the top of the frame that were completely blown out. Obviously the average metering has compensated for the relatively dark interior but I couldn't think of the best way to keep those bright whites under control (on a bracketed exposure).
I'm extremely interested in your Northscape courses so am bargaining with my wife for a weekend off! I've got long-weekend in Florence next w/e and a short safari in SA coming up in April so I'm trying to practice my skills as much as poss in preparation!
EnigmaPhoto 15 487 United Kingdom
15 Feb 2007 2:53PM
I've only been trying HDR in the last month with Photomatix so I'm no expert. So far I've only ever had had a few problems with blown highlights.

I've tried two things to help.

1) Reduce your exposure settings for your middle bracket (i.e. drop it 1/2 or full stop). Depending on your camera and settings it should automatically adjust +/- 2EV of the middle exposure.

2) If you shoot in RAW, open each RAW and expose them to where you think you think you are getting enough detail in each exposure and save as JPG. run each JPG through Photomatix and tell it what your EV values are.

Keith is giving great advice too, and looking at some of his HDR shots, he will certainly be a fountain of knowledge in months to come.
keithh 16 25.7k 33 Wallis And Futuna
15 Feb 2007 3:03PM
I wouldn't use the camera in auto bracket and it's generally agreed on HDR user forums, in fact almost universally, that if you shoot in RAW, then apply a tone curve, white balance - and that's it, do nothing else. Develop it as a 16bit tiff and then go onto your chosen HDR/Mapping software from there.
culturedcanvas 15 4.7k 59 United Kingdom
15 Feb 2007 3:03PM
There is also another trick here which is to shoot for specific items in the shot. These 'correct' exposures can then be layered over your tone mapped image to provide valuable missing details.

For instance, it can be difficult to incorporate moving people in a scene. Ive uploaded a HDR image today that has people in the takeaway in the shot.

These people on the original were ghosted - and hence an exposure for this section was placed as a layer over the image, colour matched and temp matched and then the rest of the layer erased.

This is also a useful tool with certain highlight areas - such as very bright lamps. Making the correct exposures at the time of taking the shot also makes a huge difference. 2 stop as mentioned is about right for any scene that actually NEEDS hdr!!

Also bear in mind that some scene are a little harder to recreate in HDR than others.

Dan

EDIT - although photomatix (r other such software) will do a half decent job of processing raw files (see todays upload done straight from the raw) it will not perform as well as processing the raw files first.
HowardA 13 231
15 Feb 2007 3:12PM
Thanks Dean. Strange coincidence as I was just looking at your HMS Belfast pics! I think I'll try the route of dropping down the first exposure by half a stop. Re. Photomatix - where within the program do you give it your EV values? So far I've just imported the jpgs, generated the HDR and tonemapped (trialling both the Details Enhancer and the Tone Compressor which give very different, but good, results). Ta, Howard
PatrickSmith 15 1.2k 2 United States
15 Feb 2007 3:14PM
Dan wrote:

Quote:... it will not perform as well as processing the raw files first.


Agreed. I've tried straight from raw, but it is good to get a little more control and process them to tiffs first.

And I also agree with what has already been written. -2, -1, 0, +1, +2 is about right for most situations. Sometimes you have to go beyond that to -3 or +3 as long as you still have some detail in each shot. If you don't get the whole dynamic range, the resulting HDR images start looking 'really strange!'

Patrick
culturedcanvas 15 4.7k 59 United Kingdom
15 Feb 2007 3:16PM
I usually work something like this :

-6 -4 -2 0 +2 +4 +6

Though it does depend on the scene. There's no point in shootintg HDR if the dynamic range of the scene doesnt actually demand it. There are occasions where I use 1.5 stops between the two, but never only 1 stop.

Dan
HowardA 13 231
15 Feb 2007 3:21PM
Thanks Keith, Dan and Patrick. Some very useful pointers from all of you. It's not that I wasn't happy with the result in general - really was just trying to work out a way to fix very specific burnt-out regions (Dan, I understand your note about lamps in particular). I'm extremely new to the notion of tone-mapping and HDR practices and should perhaps give it plenty of time and effort before wanting to 'have it all'. My biggest concern was for a brochure shoot in a couple of months time (hotel interiors) and concern over blowing out lighting within the rooms.
Howard
keithh 16 25.7k 33 Wallis And Futuna
15 Feb 2007 3:23PM
However you meter for your series of shots what the software looks for is evenly spaced images in terms of stop difference.

Running a series of shots at 2 stops but throwing a 1 stop in there does nothing for the image.
The software calculates a weighted average of the pixel values for each frame after linearization and division by the frame exposure. The weighting is a function of the pixel value of the frame and intended to favor the best exposed pixels. So it is unlikely that a series of 2 stop images will not contain enough information and enough overlap to deal with any eventuality.

It's night shots, especially those which contain a lot of bright light and neon that benefit from a one stop difference as this will cut down on noise issues being introduced and you'll be surprised how much wider in dynamics the image is as opposed to it's daylight equivalant.
culturedcanvas 15 4.7k 59 United Kingdom
15 Feb 2007 3:25PM
As Keith has already mentioned the important factors are first and last shot and the mid exposure. The composition will also affect this significantly ... in respect of how large the brighest light source is within the scene. The tone mapping will work well with large lamps and light sources however the smaller the light source and the more you under exposure, the less information there is for the software to process.

This is obviously something to think about at the time of taking the shot. It then gives you the option to either shoot with the idea of adding a layer after tone mapping, or forces you to adjust the composition to account for the differences in dominance of the shadows and highlights within the scene.

Dan

EDIT - Keith has essentially covered this in the previous post. The information that is retained is crucial and as mentioned smaller light sources will increase the dynamic range of the shot.
EnigmaPhoto 15 487 United Kingdom
15 Feb 2007 3:34PM
Fantastic information in this thread.

I'll have to explore this overlapping of a final layer following tone mapping. This is new to me and can only imagine the possibilities.

HDR has opened a new perspective to digital imaging to me. Hmmm, might even go e2 again based on just this one thread.
PatrickSmith 15 1.2k 2 United States
15 Feb 2007 3:45PM
Howard wrote:

Quote:....really was just trying to work out a way to fix very specific burnt-out regions


It was said just above, but another way of saying it is; Just make sure that in the darkest image, the brightest areas are properly exposed. The program needs good information in the brightest and darkest areas of an image set in order to produce a good overall image.

Patrick
HowardA 13 231
15 Feb 2007 3:55PM
Terrific - there's a lot more info there than I could ever have hoped for...thanks to you all for your time, it's very much appreciated. If anyone's ever tempted to try Chester cathedral then drop me a line as I work just 2 minutes around the corner. I know there seems to be a glut of 'church work' going on at the moment but they (as environments) seem to respond well to the treatment and produce fairly consistent results.
Howard

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