HDR Advice needed

vulcan57

Hi all

I have seen many HDR images and thought I would have a go myself as they look so good. I have looked at a load of tutorials and have tried several times now but keep hitting one problem. I have used a single image and adjusted the exposure by +1 and -1 to give me three images including the original. I then go to File> automate> mergeHDR and select the three images and press ok. All I keep getting is the message "there is not enough dynamic range in these photos to construct a useful HDR image". I have tried about 6 different images and changed the exposure to +2 and -2 also with no success. Any ideas as to what I am doing wrong?

Corkfeen

Why don't you just take 3 shots at different exposures?

Pete67

Are you using a single raw image to start with? There is more dynamic range captured in a raw image than a jpeg, so when you adjust the exposure up/down 1 or 2 stops in the raw image and export to jpegs you should get a set of three images with enough dynamic range to construct a hdr image.

vulcan57

Corkfeen wrote: »

Why don't you just take 3 shots at different exposures?

1. The tutorials say that you can do it this way, and
2. I have been trying this evening and dont have three photos handy at different exposures.

I will try and take three pictures at different exposures when I get a chance, but I was just wondering what the problem is that it won't work for me like it says in the tutorials. Thanks for the suggestion though.

vulcan57

Pete67 wrote: »

Are you using a single raw image to start with? There is more dynamic range captured in a raw image than a jpeg, so when you adjust the exposure up/down 1 or 2 stops in the raw image and export to jpegs you should get a set of three images with enough dynamic range to construct a hdr image.

I did for the first one but it didn't work and the message came up. The other times I just used the exposure under image> adjustments

Trev M

Im just wondering if th images are particularly dark that you attempting to use of the HDR?

Maybe post a sample of the lmage?

Zillah

Using three versions of the same modified jpeg is not going to work, because you cannot add information to the photo that is not there.

The best way to get a HDR is to shoot three (or more) different images at different exposures and merge those together. I'm pretty sure photoshop is telling you that there is insufficient range because it sees your three modified images as the same image.

Danbo!

If you use a raw file you can change the exposure and it should be recognised, don't think it will work with a jpeg.

CabanSail

A RAW file will have at least 3 stops either side already, you should be able to recover detail without resorting to HDR

gary82

Have you tried specialised HDR software such as Photomatix? I don't have photoshop but I do any HDR work in Photomatix.

Zillah wrote: »

Using three versions of the same modified jpeg is not going to work, because you cannot add information to the photo that is not there.

I disagree. And I've heard this point made a lot on here.

It's time to defend the humble jpeg. Ok so here's an example from one of my JPEG images... surely the final image does have a much higher dynamic range?

5uspect

No it doesn't. You haven't added any detail, you've only shifted the numbers about a bit.
You would get the same result with the burn and dodge tools and all they really do is change the luminance values. This is not a HDR.

High Dynamic Range means exactly that, High Dynamic Range. In digital signal processing dynamic range is essentially a measure of the degree of fidelity of reproducing an analogue signal with an analogue to digital converter (between a max and a min). In photography this is the camera's sensor.

JPEG is only 8bit per channel. It can only store 2^8 or 256 different bins of greyscale.
Most SLR sensors are either 12 or 14 bit (4096 and 16384 bins).
Therefore shooting RAW gives you significantly more dynamic range.
HDRs are generally considered to be up to 32 bit but this is an enormous amount of data.

So with a scene that has a lot of tonal range you need a camera with a lot of dynamic range to capture all that shadow and light, just as you need a good microphone to capture all the sounds of a recording.

By taking several exposures you can fill in the gaps in the tonal range of your camera by shifting the exposure (and hence the light levels recorded by the camera's dynamic range..
So if you're shooting RAW you have to take fewer shots as each shot covers more of the tonal range than the JPEG.

So what you have is something that looks pretty but isn't HDR.

vulcan57

Thanks lads for all the advice and comments. One other question, are there certain types of photos that lend themselves to HDR more than others?.

5uspect

Sure, sometimes you want to have high dynamic range in an image.
You may have a dark room with a window but you want to get good detail in the dark room yet see what's going on outside the window. A lot of the time you can use a grad filter on the sky to balance out the lights and the darks but with geometries other than sky-horizon-foreground you probably need to do HDR.

Tone mapping tends to be hideously over done with a lot of sunsets and landscape shots to a degree that many people avoid HDR.

Zillah

gary82 wrote: »

I disagree. And I've heard this point made a lot on here.

That's nice. As said, all you did was an automated dodge/burn process. Which is not entirely worthless in and of itself, but it's not HDR.