Just for context, let me say that I’m still relatively unskilled in Gimp…
I would like to modify part of a photo, for example a .jpg photo. For instance, I want to adjust the exposure or lighting of some sub-area of the whole photo. How can I do that?
The context of my question is as follows. Without using a neutral density filter, often it’s very difficult (nearly impossible!) to shoot certain scenes so that all parts of the image have the optimal exposure. For example, the sky might have the right exposure but a building or foliage might be too dark. Or, depending on your choice of image area for metering measurement, the ground/foliage might be properly exposed but the sky over-exposed. I have many photos right now for which I’d like to lighten the dark areas without over-exposing the sky.
I’ve tried playing with selecting a rectangle and changing lighting but I must be making user errors. Could someone please point me in the right direction…?
Thanks for your replies. In general, I anticipate that I will want to edit/modify photos to do things such as:
Luminosity (exposure?) changes
Coloration
Shadow reduction
Contrast
Basically, I see the need to do this on some portion of the visible area of the image. It sounds as though the masks and layers are the right capabilities. I need to go read up on those.
However, at this time I’m not clear on how to select the area to edit. It will almost never be a rectangular area. I watched some YouTube videos and tutorials, but it wasn’t clear on how the author selected the tool or how he or she was outlining the area on which to operate.
I’m happy to go read up on it if someone could point me to a good explanation whether it be a tutorial video or a written article. Perhaps I just haven’t viewed the good ones yet…
The link that @paperdigits gave above, and mine should get you a decent start on this type of approach to editing. (And of course we’re here if you have questions).
Have you also looked into HDR processing? It’s a technique where you take your bracketed exposures and compile them into a single image. There are many tools available: HDRLuminance, HDRMerge, Google’s NIK Collection, etc. It does help if you have a nice locked down series of shots to do this, but there are some great tools to align images before you process them.
One word of caution, people do tend to over do it a bit. Don’t go overboard.
An easier route into using masks may be to use Darktable, which can be used on normal images as well as RAW files. I find its masking very quick and easy to use for things like gradients and basic-ish shapes, optionally with feathering and blurring, and applied areas can be further tailored based on tone, hue and lightness. There’s a certain elegance to it as, instead of using raster greyscale images as masks as in GIMP/Photoshop, masks are made from quite often simple vector shapes and are usually easy to edit on the fly after creation.
With your sky examples, you could start off using a single gradient mask.
Luminosity masks are the best way when you want to apply a filter or tool effect only on a specific portion of the image only. Sometimes, however, luminosity mask covers or uncovers more than we need. In that case, painting applied layer mask with white or black will correct mask’s border according to our needs.
In order to paint on the mask, we need to click on the layer mask and choose the colour for our brush. White is opaque and protects painted area from changes. Black exposes painted area for editing. Always use fuzzy soft brush and change its size to paint precisely over details. You can also change the opacity for smooth blending. I hope this will be useful for you. In case you have some questions or I’m not clear enough, please write me.
