id like to know how to darken only a specific part of an image like the one below
I think the answer @Sidneyvan94 is looking for is much more basic than some others may be thinking.
- Create a new layer in your file.
- Fill with black.
- Add a mask to the black layer.
- Using a soft brush with the colour set to black, paint on the mask the areas of the photo you wish to have showing.
- Create a new layer
- Pick a paint brush with a nice soft edge
- Set your brush colour to black
- Paint away the areas you want black
You can mess with the layer modes after either choice to see if you can get a more desirable result.
In Photoshop: Adjusting layers and layer masks on them are maybe the most versatile way to go. Sometimes adjusting brightness & contrast or curves are not the only viable tunings, it is possible meaningfully to turn also some color to be darker or lighter by adjusting selectively Hue & saturation & luminosity.
Advanced users insert a layer that is not in blending mode "Normal" but something else; maybe "Hard light". It affects easily radically to the color and lightness of underlying image. Hard light means that painted color is considered to be light or darkness, coloured light or darkness, too.
There are incredibly many ways to achieve same results because in Photoshop so many controls are built to affect luminosity.
Warning: To get a 100% realistic result, quite fine and complex crafting may be needed. For ex. if one wants to turn a fully lighted room to have only light on the stage, anything else must be tinkered to have it's light as it's a glow from the stage. This means more light on the stageside of every object. Every well visible object must be crafted individually. The working hours pile easily in this kind of job. Fortunately artistically viable results do not have to be accurate.