What is HDR?

Zascar

When browsing Flickr I see a lot of very cool photos that say they are done with HDR.

I've done a search on the web and read some descriptions but its still not clear to me what it is and how you do it?

Can anyone enlighten me?
Thanks

PopeBuckfastXVI

HDR is High Dynamic Range

It means that the photos contain more range than the camera can pick up in one go.

You know when you take a picture of something like a sunset, you can either expose to get the sky with detail, so that the land is completely dark, and you can't see any detail, or you expose for the land and then the sky is completely washed out? Well HDR addresses this problem.

The technique involves taking multiple pictures of the same scene, at different exposure levels. Typically you would take at least three photos, but some people take up to nine. You would want to use a tripod to make sure you are taking the exact same scene in each photo.

So now you have 3 photos (for instance), 1 with detail in the sky, 1 with detail in the distant/middle ground and 1 with detail in the foreground. You then use a 'tone mapping' software to merge the 3 photos together into 1 HDR Image with detail in the sky, the middle ground and the foreground.

The concept works anywhere where you would be dropping detail in 1 part of the image to gain detail in another, think about something like stained glass windows in a church.

Hope this helps!

sasar

This might help you to better understand what HDR is:
http://www.naturescapes.net/072006/rh0706_1.htm

elven

FAQs people, FAQs!!! there's a whole bunch of stuff there...

pete4130

In simple terms, its a set of identical images with different exposures, some under, some over and one proerply exposed. The underexopsed shots catch the detail in highlight areas, the properly exposed shot gets the detail in the midtone areas and the overexposed shots get the detail from the dark/shadow areas.
These are then blended together, either in photoshop or some other HDR software and makes a "perfect" exposure so so detail is lost in either the shadow or highlights.

A "pseudo" HDR can be created from 1 file, where the software changes the exposure itself and then blends these together. It's not really a true HDR as you aren't getting in any mroe detail than was in the original file.

It is very easy to overdo/overcook HDR shots and make them look more like animation or paintings and thats what alot of HDR's will probably look like when you search for them on flickr.

HDR's tend to giove great depth and a really strong texture in the images. If you check my flickr, you'll see the some interior shots I've taken that are HDR butI've tried to keep them as natural looking as possible.

Zascar

elven wrote: »

FAQs people, FAQs!!! there's a whole bunch of stuff there...

This is the only link to HDR in the FAQ

Thanks Pope and Pete your information is really useful, exactly what I was after

amcinroy

This might demonstrate what HDR is all about.

Thirdfox

pete4130 wrote: »

A "pseudo" HDR can be created from 1 file, where the software changes the exposure itself and then blends these together. It's not really a true HDR as you aren't getting in any mroe detail than was in the original file.

I don't quite agree with that - shooting RAW you can get up to 2.5 stops back from highlights and maybe 1-2 stops from the shadows. Creating a HDR image from one raw image will give more visible dynamic range (less clipping of highlights or totally black shadows) than the solitary jpeg or unmodified raw image.

amcinroy

Pete,

I agree with Thirdfox.

My own experience is that pseudo HDR from a single RAW can extract more detail than a single RAW conversion, even with a strong curves adjustment within the RAW conversion software.

Andy

Thirdfox

Pete,

Here is a good example of what I mean:
http://www.dpreview.com/reviews/nikond300/page20.asp
see the bottom of the page - with a -2.5 compensation into ACR detail is recovered from the clipped highlights, so if you were to make a pseudo-HDR image from the file you would actually get more dynamic range and detail.

amcinroy

But Thirdfox, I think the point that Pete is trying to make is this.

Say, in your example image, ACR had been used just to bring the highlights back and to boost the shadows (through an inverse S curve). This perhaps is equivalent to, but far simpler than, the pseudo HDR approach. I think your arguement is flawed for that reason but I do think there are other more complex reasons why pseudo HDR does appear to work.

Even Photomatix themselves admit that pseudo-HDR will at best re-produce the dynamic range of the initial RAW file.

That really doesn't explain my own findings however. There is certainly more to it than what you have suggested.

Andy

pete4130

Thanks Andy & Thirdfox,

Thats exactly what I meant, an HDR from 1 file will only use the existing Dynamic Range of a single file, just as bringing in the same file on different layers and editing different parts of the image on a different layers. The bright sky for example worked on one duplicate layer, the shadow detail worked on a different layer. All this to extract the best detail/dynamic range from the single file.

Programs like Photomatix simply do this alot faster and in most cases alot better, although from experience it can create alot of noise/hot pixels in dark areas. Some images are better suited to being HDR'd from a single file than others. I do agree its easier to get a better DR with a pseudo HDR than from editing a single RAW file on its own.

A pseudo HDR is still only using the data contained in one shot. That 1 shot might be able to get details +/- 2 stops above and below. It doesn't change the fact that its still the dynamic range from that single file and therefore not a true HDR.

I probably didn't explain myself clearly in previous posts (hard top type freely in work!) but I do think we are all singing from the same hymn sheet here.

fguihen

so you need at least 3 images all with different exposures.

so first i expose for the focus point of the photo,
next i move the camera to the sky, meter for that and get another image.
then i point the camera at the foreground , meter for that and get another image.


with all the moving of the camera how do you ensure your pointing the camera at the exact same point each time so there is no variation when alligning the images?

pete4130

fguihen,

No, you've misunderstood. You do need at least 3 images, but you don't move the camera (hence tripod is essential and cable release if possible!).
Your camera should have a bracketing function (this allows you to take 3 pictures and it automatically makes 1 exposure under, 1 spot on and 1 over). and thats your 3 files for creating the HDR.

If your cam doesn't have bracketing function, then you can carefully change the exposure manually. Remember to change the shutter speed only and leave the aperture the same for all 3 shots. If you change the aperture for each shot, the depth of field will be different for each shot.

Hope this helps clear things up a bit?

Pete.