Levels and Curves are among the most common and basic Photoshop adjustments to get the lightness or darkness levels on yours image right. Before you get into Levels though, it is important to know how you can gauge them. Most cameras that are even moderately advanced in features display a visual representation of the lightness and darkness levels of an image in the form of ‘histograms’.
To view the histogram on a DSLR simply go to the playback menu and use the cursor wheel/arrow keys to activate the histogram view. On Photoshop, you can go to the MENU on top and access the histogram view under IMAGE – ADJUST – LEVELS.
A photography histogram is pretty simple to read. The mountains on the left display the amount of low key (or dark) areas, the ones on the right display the high key (or lighter) areas. The mid region displays the mod tones. An image with lots of contrasting tones would display lots of peaks! To get an absolutely clear idea of this, check out the histogram of an image that contains only pure black and pure white – that’s 2 tones alone for you with no shades of grey in between –
Now, as already mentioned, a photograph would definitely have many more of these ‘peaks’ depicting high key and low key areas.
On the Photoshop ‘LEVELS’ option you can change the tonal range of the image by moving the black, grey and white sliders to change the blacks, grays or whites towards one of the other tones. For example, moving the first slider towards the right would transform your blacks towards lighter shades, and moving the right most slider (white) to the left will darken the high key areas.
This is the simplest form of a histogram which we are using to, as yet deal with a black and white photograph. Notice the ‘Channels’ set to RGB on the LEVELS screen grab above. You could select any one of the 3 primary colors Red, Green or Blue to change the tonal range of that colour alone. On a black and white image, doing this results in giving the image a colour tint – try it!
On a colour image, it is great practice to get the colours just right by using the histogram and LEVELS to adjust the tonal ranges of red, green and blue in an image. Use the ‘PREVIEW’ button selection on the LEVELS window to toggle between BEFORE-AFTER views of the image.
In-cameras histograms can also be used to simply check if the picture you just shot has a good tonal range. This could be particularly important for a landscape photographer attempting to squeeze in as many ‘zones’ into the photograph as possible. To the photographer looking to shoot a high key portrait, the histogram should ideally display an increasing trend towards the peaks on the right…you get the idea!