I am trying to use the HDR merging tool on the latest Lightroom version on Windows 10.
I then took three images of the same landscape scene : one with "correct exposure" on my camera, a second one under-exposed (to get details on my foreground) and a third one over-exposed (to get details on the sky). Which I think is the basic way to use the Lightroom HDR merging tool.
However, when I merge these three pictures with Lightroom (with no automatic parameters, so that I can compare with my raw pictures), I don't get the details I have on the separated pictures.
Furthermore, when I only pick the under and over-exposed picture to do the HDR merge, I get a result which is very similar of the correctly exposed picture, meaning that I cannot manage to get any advantage of using the HDR merge tool rather than a simple picture. I have to say I am a bit disappointed, but I think I must be doing it the wrong way...
Is there any prerequisites I could possibly miss? Or any requisite on the shoot? What is the proper way to use HDR?
Because you did not check any automatic parameters, your HDR image is still undeveloped. When you edit it, you will find that you'll have far more headroom in both the highlights and the shadows than the individual images have. That is what HDR is all about.
Oh well, I didn't realize that! It actually drastically reduced the noise in both shadows and highlights. Thank you 🙂
So, can it be seen as a way of reducing noise in pictures? What does happen if I use HDR with close pictures in terms of exposure?
Very little extra happens when you HDR-merge just a few close-exposed pictures - with (say) 1 stop difference between - compared with processing a single well exposed Raw. Apart from maybe suffering 'ghosting' from subject movement or whatever.
You will see the point of this technique much more clearly with much more widely-exposed pictures - 2 or 3 stops between - including some that would be considered badly overexposed in normal terms, and some that would be considered badly underexposed in normal terms. But taken together, these can all contribute to building a 'virtual scene' that smoothly represents the subject across a very wide range of brightness.
In effect you are then re-exposing a new conventional image out of this 'virtual scene'. To supply only a narrow range of bracketed shots would be to impoverish what overall scene brightness this 'virtual scene' includes - so it offers little more opportunity for adjustment, than a single Raw exposure could have afforded.
It is clear to see this extra adjustability in the 'supercharged' Exposure and Contrast controls IMO, and not only by pixel-peeping shadow quality or whatever. But that is only apparent provided you have bracketed broadly in the first place.
You may find linked Adobe document helpful when deciding upon best exposure options and the number of images to use when using HDR in Lightroom Classic https://helpx.adobe.com/lightroom-classic/help/hdr-photo-merge.html
An important start is to understand what HDR is and why you may need it in one situation and not in another. HDR stands for "high dynamic range", meaning it is a way to record a scene that has a too high dynamic range for your camera sensor. A good example is an indoor/outdoor scene, like the interior of a room with the outside world shown through the windows. Your camera sensor cannot record such a high dynamic range, so no matter what exposure you choose, a single raw image will always either have blown out highlights or pitch black shadows. It will be impossible to shoot a single raw image that has good detail in both the highlights and the shadows. This is what HDR can solve. HDR will combine the highlights of the darkest exposures and the shadows of the brightest exposures into one image.
If you scene has a normal to low dynamic range, such as an outdoor shot on an overcast day, then using HDR is meaningless. Your camera is very well capable of recording the detail of the entire dynamic range, so trying to increase that capability by using HDR does not add anything you do not already have. It may in fact give you a poorer image, because of alignment and/or ghosting issues.