[GainfulShrimp]

What is HDR and Tone Mapping?

Because of the limited dynamic range of camera sensors, exposing a shot correctly often means losing details from either highlights or shadows, or both in extreme cases (depending on the scene).
High Dynamic Range imaging allows more of these highlight and shadow details to be retained, by combining several exposures of the same scene at different shutter speeds. The highlights are used from 'underexposed' shots and the shadow information is taken from 'overexposed' shots. By combining five or more exposures, a huge dynamic range is possible.
Tone Mapping is used as a method of scaling (i.e. mapping) the high range of luminance values contained in an HDR image into a range which looks good on devices which have a limited dynamic range - like monitors and printers. A tone reproduction operator is used during tone mapping to retain perceptual qualities of the original scene - such as contrast and fine detail.


About this tutorial

I'll use Photomatix Pro 2.2.1 to combine several shots, taken on a tripod, into an HDR image - Exposure Blending. I'll then use the Tone Mapping feature of Photomatix on the generated HDR image, saving it as a 16 bit TIF. Final touches and webification will be done in Photoshop CS2. There are some other options for non-tripod shots discussed later, too.

I've bought the full version of Photomatix, but a trial version is available.

I've split this into three main steps: taking the photos, blending them to make an HDR image and finally tone mapping the HDR image. Then there's some more of my waffle to round it off.

1. Taking the photos

I used a Canon 20D on a decent tripod to take several shots of our living room and french doors. A very boring subject, but the view outside the window included some bright stuff outside and the shadows in the room were relatively dark... so it was a good scene for demonstrating what HDR can do elsewhere with more interesting subjects.

Because the idea is to capture as much detail as possible and use the full dynamic range available from the sensor, I shot in RAW format (I always shoot in RAW, in truth, but it was a really good idea on this occasion). I selected ISO100 to get nice noise-free images. I used mirror lockup (aka MLU - selectable from the Custom Functions menu) and self-timer to help reduce any shake introduced by my finger on the shutter or the mirror action. (Use a remote shutter release instead of self timer, if you prefer.)

I wanted a large depth of field - to get both the room contents and outside scenery in focus - so I selected f/16 aperture in M (manual) mode. The camera's evaluative metering recommended 1/2sec exposure time.
I wanted to cover a wide range of exposure values: -2EV, -1EV, 0, +1EV, +2EV. One stop/EV increase/overexposure requires doubling the light to the sensor - i.e. doubling the exposure time. Likewise, decreasing by one stop (underexposing) is achieved by halving the light to the sensor - i.e. halving the exposure time. Aperture should remain constant at f/16, so that each picture has an identical depth of field.
So, given our rough estimate of 1/2sec exposure time, these are the manual settings that I used:

+2EV = 2 secs
+1EV = 1 second
0EV = 1/2 second
-1EV = 1/4 second
-2EV = 1/8 second

This resulted in five shots, which looked like this:

2 stops overexposed (+2EV): 2secs, f/16, ISO 100


1 stop overexposed (+1EV): 1secs, f/16, ISO 100


correctly exposed: 1/2sec, f/16, ISO 100


1 stop underexposed (-1EV): 1/4sec, f/16, ISO 100


2 stops underexposed (-2EV): 1/8sec, f/16, ISO 100


In the next part of the tutorial, I'll combine the five images using Photomatix's Exposure Blending feature.

2. Creating the HDR image

The RAW files were converted into unsharpened 16 bit TIFs (low constrast, otherwise default settings - use your favourite RAW processor). In Photomatix, select Generate HDR from the HDRI menu. This opens a dialog to open your images. I clicked browse, selected my five images and clicked OK.
A window then pops up called "Exposure Values for Generation HDR Image", asking for confirmation of the Exposure Value guesses made by the software:



In this case, the guesses are correct: 2, 1, 0, -1, -2... so I just click OK. On the next windows, I select Use standard response curve (recommended) and click OK:



After a few seconds processing, the HDR image is displayed. Because the colour space of the display can't show the full range of tones included in the image, an 'HDR viewer' window is displayed so you can check details from anywhere on the image, like this:



Now we've got our HDR image, we can use Tone Mapping to process the dynamic range back into something we can easily display as a normal 8 bit JPEG...

3. Tone Mapping

Still in Photomatix, from the HDRI menu, select Tone Mapping. A settings window appears together with a preview of the tone mapped image:



You can read the online help or experiment with each setting to find out what it does. I used the default settings here apart from setting output pixel depth to 48bit, then clicked OK.

I saved a 16 bit TIF and then opened the file in Photoshop to apply some finishing touches.

Tone mapped image:

http://matthewh.com/images/tutorials...2336-01-TM.jpg

After sharpening, levels and curves adjustment:



So that's it - a bit pants but it shows what can be done with a more interesting subject and some imagination, at least...

Next section discusses further stuff to try and how to use Tone Mapping on single RAWs.

Problems encountered and things to try next time

There are a couple of snags with my image above - apart from the fact that it's an awfully boring arbitrary shot of my living room - (1) parts of the sky are still blown and (2) Ann has turned into a two headed monster due to her moving slightly in between my multiple exposures.
To address the first issue, you would simply take more shots to feed into Photomatix to make sure you covered both the highlights and shadows more comprehensively.
The second issue is trickier to resolve and demonstrates a problem with this technique - namely it only really works well with static subjects!

Something else to try is using an image stabilized lens with a steady hand, autobracketing (set it at +/-2EV) and continuous shooting mode... which allows you to get almost-aligned shots without the use of a tripod. I achieved a reasonable boring HDR pic this way, but a tripod is preferable for sure. (Also, notice the cat at the bottom of this pic moved between the three frames, so it now looks like a ghostly cat...) During the 'response curve setting' step of Exposure Blending, you can check a box to tell Photomatix to attempt to align the images before it blends them. This seems to work reasonably well.

If you use Photoshop CS2, you could use it to generate HDR images (look in the File > Automate menu), but it's not as easy as using Photomatix because CS2 insists on using many images and is much more picky.


How to use these techniques on moving subjects (or single RAW files)

It's possible to treat a single RAW file as an HDR image... which you may think is cheating, but it actually works quite well with certain images.
The dynamic range of a RAW file is quite a bit more than that of an 8 bit JPEG, so it makes sense to try to squeeze the maximum amount out of these files using Tone Mapping.

To do this, you should try to choose a subject with a reasonable dynamic range to start with - don't expect miracles - remember we're not creating an image with a dynamic range bigger than the sensor, like we can with Exposure Blending. Then shoot in RAW, overexposing slightly: err on the side of losing a bit of highlight detail in the sky but keeping as much shadow detail as possible. You need a nice, clean, noise-free image for this, so use as low an ISO value as you can.
During RAW conversion, bring down the exposure slightly to make up for the slight overexposure and save as a 16 bit TIF again.

Open the TIF in Photomatix, and select Tone Mapping from the HDRI menu. You'll need to be a bit more careful tweaking the settings when using a single input file as the source to get the best results. Here is an example I created from a single RAW file:

Result using my normal RAW workflow:
matthewh.com gallery - France 2005/20050719-161024-01

Result after tone mapping and some curves adjustment:
matthewh.com gallery - High Dynamic Range (HDR)/Montaubin

Good luck with your HDRs and please do share the results!

Cheers,

GS

[stepheno]

Thanks for sharing your tutorial GS. It will be helpful to members

[silkstone]

That's very good GS - many thanks.

[Angela]

Thanks GS! That is gong to be incredibly helpful!

[j sotelo]

I'll keep it in mind I have Photomatix Pro 2.4 but it should work the same.

THANKS !

[GainfulShrimp]

Cheers chaps.

I think I'd better take a look at the latest version of Photomatix Pro then... it's not something I've thought of updating since I initially bought it quite a while ago. :o

[fionaB]

great tutorial......... will put photomatix on my list of "wants" have never been into HDR but i think its time to start experimenting with the dark nights coming in

Fi

[Dave]

How to make an impact on the site .... great tutorial

[Steve]

Absolutely fantastic HDR tutorial. Thank you very much for sharing it with us.

Reputation points duly added

[P-E]

Nice one

[simpbow]

Great tutorial, got trial software to use so thiswill be a great help.

[j sotelo]

you can download the trial version at HDR Photomatix Pro

[dogdots]

Very informative tutorial. Thanks!

[Les Meehan]

I think this sets the standard for clear and very useful tutorials!! I will take this on board when doing some of mine.

Nice one!

Les

[Charlotte]

Great tutorial, many thanks

[b.van_der_dylan]

brilliant, thanks for putting that one together...

[Pentaxbuff]

Hi Gainful...
Is there a tutorial here doing exactly what you are showing, but with PS ? Or else, is the tecnique the very same?
I am trying to learn how to "merge" auto-bracketed pics from the Pentax K10D in Photoshop. I have V.8 of PS and also Elements 4.
Great if you could help!
Cheers.

[j sotelo]

Photoshop CS2 (v.9) and CS3 (v.10) are the ones that have Merge to HDR option

you can always download the trial version of photomatix in my post above.

[Pentaxbuff]

Thanks J.
I'll do that.
Edited:
I've downloaded the trial version and will get some braketed shots asap; this looks simpler than with PS, Am I right?
Thanks again for the help.

[GainfulShrimp]

Yes - in my opinion it's much easier in Photomatix.

Doing a merge in Photoshop is almost as easy, but there's no automated options to align the images so it's more important to use a tripod for your bracketed shots. With Photomatix, you can often get away with handheld brackets if you have a steady hand, use continuous shooting and autobracketing.

Also, Photoshop requires a much larger range of exposures or it will complain and refuse to combine them. Photomatix works fine with -2, 0, +2 EV shots, but Photoshop might moan unless you give it e.g. -3, -2, -1, 0, +1, +2, +3... which means more exposures per HDR and slightly more messing around.

If you decide PS is the way for you, look up "Merge to HDR" in the online help to get started. From memory, it's not tricky to do once you have enough images to feed it.

[GainfulShrimp]

Sorry - just realised that I think Merge to HDR is only available in the latest couple of versions of PS. You might be out of luck with PS8 and Elements 4, I'm afraid.

... but on the bright side, Photomatix is easier to use for this, I reckon.

[digimom]

interesting...

[Tom-Tec]

Brilliant guide ok , tried it out today and it worked well and really enjoyed it .

Firstly did it with bracketing set to 3 , 1+, 0, 1-

Then i did it with 5 stops, 2+ 1+ 0 1- 2- and it worked well but my tripod is not sturdy enough as each time i had to adjust manual o/u it slightly moved

but got there in the end

great stuff

TT

[Rob Barron]

Hi TT, not seen this thread much lately as it was mostly active a couple of years ago (just mentioning in case you didn't see too many replies).

In terms of the number of photos, you need to think carefully about this as a lot of people make the mistake of simply taking a 3-shot bracketed sequence and assuming this will be enough. Sometimes it will but often it won't and this is the main reason why so many HDR shots look false and unnatural.

You need to think about it this way:

Colours change as they get lighter or darker. Whilst blue colours will retain a blueness even when quite dark, colours at the red end of the specturm lose their colour very quickly. Hence if you have what the human eye perceives to be a dark red colour, the sensor will often not record it as a red colour at all as it actually looks quite different, maybe a dark grey or even a bluer colour (the last part of the colour specturm to disappear in darkness, hence night time usually looks blue :o)

This is also often a problem with large expanses of green, eg grass, foliage etc. When taken at - stop values, they often look very muddy and colourless so lightening them up in HDR does not reveal true colour. So if you want to do natural looking landscapes, shots which often include the fullest range of tonal variations and colour hues, you need to take more shots, maybe 7-9 rather than 3 or even 5.

Hope that makes sense for you. Happy to answer questions on this if you need further help.

Cheers,
Rob

[Charlotte]

I respectfully disagree with the "more is better" theory with regard to the number of shots in HDR :

If your camera will bracket using 2-stop intervals, then 3 shots will more than comfortably cover a large enough dynamic range to get great results, using +2 stops, 0, and -2 stops. Of course, if your camera will only bracket using 1 stop intervals, then yes you'd have to take 5 shots to capture the full dymanic range.

HDR will usually be used for architecture and landscape images. Whilst you can be pretty sure that buildings will not move in between shots that cannot be said for landscape shots, even when using a tripod ... wind/breeze will be blowing leaves/grass etc. about, however minutely, and the more shots you take the more likely you will get a fuzzy picture when combining multiple shots, leaving a resulting image which is unsharp (and sharpening in PP will only emphasize the problem).

In addition, with outdoor shots, the light can change in an instant, so that if you dally about, taking 7-9 shots, I believe it is here that a light-shifting problem would more likely be the cause of unnatural looking results when you try to combine shots where the light changed across the scene.

So, if your camera can bracket in 2-stop intervals, I recommend sticking with 3 shots. Even if your camera can only bracket using 1-stop intervals, you could take 5 shots but you still only need to combine 3 of them, i.e. the first (lightest), middle (midtone) and last (darkest) in your HDR software.

Not sure about your colour-changing theory Rob, I haven't heard of that before

[Boofers]

Wow, Sence when did hdr become so interesting on this forum. For me and my two penny's the whole buck for hdr is to bring in some extra tone. I think Orangepeel has it right in blending what he wants. I use curves to blend in enough detail in certain spots to make me happy. On bracketing, when I get on a kick and go out with the pod or not with the pod I use 3 shots 90% of the time. On a few trips out I have used my exposure compensation to off set the shutter for two sets for six shots. It's true you can use what you want out of those shots but I have seen some real easy blending hdr's that look good when using six shots. It just takes more time to turn the compensation down -2/3 from the first set at +1/3 as I remember. As for color changes if I understand what was said, closer exposures would make it easy on the software to make a better blend would it not ?

[Des Gardner]

Yes very interesting, I have not tried it yet, you put it over well!