Experimenting with HDR

[Stephen]

Now first of all lets get one thing straight. I'm no technical waller and don't care much for the physics of how HDR works or indeed how the software does what it does. However I have a basic understanding of what High Dynamic Range is when it comes to a digital image. Consequently I don't want to get drawn into a pointless argument about the best way of doing this or that.

I have been playing around with CS2 to try and get its Merge HDR command to work with a series of pics taken from the same raw file. I was obviously doing something wrong cos it wouldn't do it coming up with the error message that there was not enough dynamic range to create a useful HDR image, very frustrating. I have also played around with a program called Photomatix. Suffice to say if I can't suss a prog within about half an hour I am inclined to give up

Now at this point I have to give a lot of credit to PollyG. We have been communicating recently and discussing this very subject, and it was her that put me onto a different method which I am now offering to peeps here on a take it or leave basis

The photo below is one I essentially have never been happy with the end result using my usual method of balancing foreground and sky. I exposed the shot originally at a sort of compromise setting and this is how the shot looked converted from Raw without any adjustments in PS ie As Shot

http://img.photobucket.com/albums/v1.../CS_asshot.jpg

The next shot is the same file adjusted to plus 0.75 EV which was what I felt was OK for the road and foreground but obviously burnt out the sky

http://img.photobucket.com/albums/v1.../CS_plus75.jpg

Now often Adobe Camera Raw does a pretty good job set to Auto but in this instance although the sky was much better the foreground was far too underexposed. This version then is the Auto conversion setting, and is the one that I would normally use for this shot and then work on it in my usual way, Curves, etc etc.

http://img.photobucket.com/albums/v1...tosettings.jpg

The final version uses the auto version above and then using the HDR technique it is adjusted to a more pleasing point before finally some basic tweaking in PS

http://img.photobucket.com/albums/v1...SarahsHDR1.jpg

So whaddya think so far?

Basically the technique involves converting the 8bit file to 16bit then to 32bit which becomes available to the 16bit file.

The 32bit file is then converted back to 16bit. At this point a dialogue opens up called HDR conversion. In the drop down menu choose Local Adaptation and open up the Curve in the same dialogue. Using Curves adjust the image to suit and also play about Radius, I haven't noticed much difference adjusting the threshold slider, but you may. When you are happy click Ok and the file is converted. You can then adjust the file to suit in PS. I simply put a gradation in the sky. For me though the whole process has given a better result than I ever got before. As I said take it or leave it

[Saphire]

Thanks for that tutorial Stephen it was very interesting to try. I have tried in the past to use layers and not had much luck. What I normally end up doing is either burning or adding a different sky. The only problem I had trying this out was I have slight posterization which I couldn't get rid of.

[Stephen]

Mmm not sure what's going on along the top of the hill but it certainly looks odd. I feel sure that some extra tweeking of the HDR curve may help with the green shades on the hill side. Did you make some sort of selection along the top of the hill?

[Saphire]

Yes Stephen I did, I am still playing so will probably get the hang of it. I am trying with another image I may have taken it to far.

[Stephen]

Originally Posted by Saphire

Yes Robski I did, I am still playing so will probably get the hang of it. I am trying with another image I may have taken it to far.

Robski??? sure you meant me Christine
May I suggest that if you make a selection of say the sky area in order todarken it or make it more dramatic, and are using the full size image, then you should try feathering the selection by between 150-200 pixels. This will eliminate the sudden change in tone we see in your picture

[Saphire]

Sorry Stephen I could have sworn it was Robski who I was answering too. My eyes must be playing tricks

[robski]

Christine what am I being blamed for now
What is it they say ? You should of gone to spec savers

Stephen I think you have made a decent job of adjusting your image.

I have dabbled with this sort of thing in the past trying to merge images but never got anything to be happy with. I sort of came to the conclusion that this works best on images that have very little detail in part of the tonal range and you can effectively snip a bit out and pull the two ends towards the middle. See below.

Looking at your histograms of before and after seems to confirm this.

With other images and I think Christine's may fall into that catagory is the tonal compression often seems to leave parts of the scene unnaturally lit.

1) before
2) after

[Gidders]

Stephen

I have also experimented with the Merge to HDR command with different RAW conversions and goyt the same message.
I've come to the conclusion that you actually need to take shots at different exposures although I haven't tried it.

There is one particulat shot that I have taken at Westonbirt which is very contrasty and so
I've never been able to get a result that I've been happy with.
Westonbirt 2295 -0.5 exp.jpg

To retain the highlight detail it needs a 3 stop under exposure on conversion from RAW
so I was very interested to try your 32 bit conversion technique and got this result which, I think, is a huge improvement.
Westonbirt 2295 HDP conv.jpg

When working through the conversion it occured to me that what this was effectively doing was applying quite a severe
levels & curves adjustment, so I went back to the 3 stop under conversion in 16 bit and had a go with levels and curves
and came up with this result.
Westonbirt 2295 lev & curv.jpg

What ever the way of getting there, thank you for giving me the impetus to go back to this image and have another go

[Stephen]

Glad you found it useful.
Since writing the above, I have found that the CS2 merge to HDR does indeed need separate exposures with a wide enough dynamic range to be able to do the merge satisfactorily. I have then been playing around with Photomatix and found they have a free Basic version which will do the merge no problem from adjusted Raw images without the need to bracket, though obviously this is not ideal, separate exposures are the best.

The resulting HDR image either from CS2 or Photomatix Basic can then be Tonemapped in the full Photomatix CS2 Plugin and gives incredible results. I now have a licenced version of the plugin which is cheaper then the full Pro version. If you Google for Photomatix you will find all the details, it really is worth having a go with the trial version at least.