Be warned the information in this article might be useful to anyone
It is extremely important to realize where ever you fall in the photographic philosophy
spectrum, as one who might believe digital alterations should be minimized
or as one who might believe digital alterations are an essential part
of post processing images, that the output
of a scanner or digital camera is NOT FINAL and it IS NOT necessarily
the correct display output. Scanners and Digital Sensors
do their best to capture data and take their best guess at how it
should appear. A scanner or a digital camera won't know how to display
every single lighting situation and the resulting impact on contrast
or color saturation. The software governing the output of these files
is generic, but does a decent job initially.
- works on images that have originated from scanned slides, negatives
and/or a digital camera.
- considers themselves a novice, intermediate or experienced photographer.
- has ever worked on an image to print or put online.
Unless you like being generic it is essential you understand what
Levels and Curves adustments provide.
As you become familiar with the information and techniques provided in this article, you too will begin to see over time what a trained eye will instantly see when viewing images that have not been color corrected. A trained eye will instantly see areas of improvement such as color casts and/or muddled higlights/shadows.
How To Make
Option 1: Levels/Curves via the Image Menu
(See image to the left)
In Photoshop or an equivalent piece of software you can edit levels
via the Image menu.
(Image > Adjustments > Levels)
This is a satisfactory method, but a second and more flexible option exists.
Option 2: Levels/Curves via the Adjustment Layers
menu on the Layers palette window
(See image to the left)
This method is the most flexible of the two as you can easily undo, compare or change layer
settings. I'm embarassed to say I learned about this late in the game
and it is a real time saver.
Selecting Levels & The Histogram
click to enlarge
|The example image, "The Bearded Chain", provided by Geoffrey Day of Liverpool, NY.
Allows you to adjust the tonal range of an image with the use of a histogram.
Is a graph of the number of pixels at each brightness level in an image.
Pictured to the right is an unaltered image as captured from a digital camera (see the background
behind the histogram window). The histogram, the odd looking graph,
designates shadows on the left and true black is represented by a
value of 0, while highlights are on the right with white being represented
by a value of 255. The arrow in the middle represents the mid-tones
and can be adjusted from left to right to either darken or lighten
The first step of this process and the most important step
is to keep in mind the lighting scenario for your photo.
Clicking on "Auto" will tell the software to take its best guess at
what it thinks the scene should be. This will wash out "magic hour"
lighting from early morning or late evening and will devastate a sunrise/sunset.
It is always best to manually adjust levels unless you don't care.
Adjusting the histogram to color correct your image
can be done for the entire RGB spectrum and on an individual basis
for each color channel (Red, Green, and Blue).
In evaluating histogram data I look for plateaus of unused data. In
this case (see the "Levels Unadjusted" example above) the
highlights were severely under represented. Look at the right side
of the histogram. I brought the highlight arrow to the beginning
of where the data is really starting to register. I also brought in
the shadow arrow to darken the shadows as they were a little light.
Next use the pull down menu to select each color channel and repeat
the above steps. To the left are screencaptures of the adjustments I made for this
This takes some learning by experimentation
and compressing the histogram does not always provide the best results.
This again depends on the lighting conditions in your image. The
example image to the left "Blue Channel Re-Adjusted" is
after adjusting the red, green and blue. The histogram only shows
the blue channel.
I ended up backing off compressing the histogram for each channel to give a more natural appearance to the image.
How each channel ended up after a little trial and error, but with some decent educated guesses can be seen to the left in the example image "RGB Final Look".
If you go back to the RGB setting after adjusting each color channel you'll see that the composite histogram is quite different now.
If you've ever used "Auto Levels" then you'll have seen this transformation to the histogram before, but now you'll know how it's actually put together.
Selecting & Using
Allows you to adjust the tonal range of an image in an alternate fashion with the use of an Arbitrary Map versus a Histogram.
Curves can be found just like Levels as detailed above in the How
To Make Adustments portion of this article.
Curves is a very mysterious function. In many respects it can be used just like Levels and even in place of it. The most powerful aspect of Curves is that you can adjust how your image displays Black, White and Grey. There are very formal write ups on how to do this, but I think it is unnecessary to go into as most software programs now do this automatically with various functions. What I will speak to is the basic use of Curves and how that in itself can be enough to provide dramatic improvements to an image.
An Arbitrary map (see the images above) displays a line with the lower left end
representing shadows, the upper right end representing highlights
and the middle representing midtones. To adjust an image using the
Arbitrary map you click on the line to set a point and drag it around.
You can designate up to 16 points to set and adjust. If you click
a point on the far left it will represent what should be true black
and if you click a point on the far right it will represent what should
be true white. Dragging these points subtly can provide dramatic
improvements. Dragging these points drastically can create wild distortions.
The result of tweaking the black values to an extreme can be seen in the image to the left titled "Shadows RGB". Note if you shifted this point up versus to the right reversing the values "Output: 58" and "Input: 0" the shadows would become much lighter versus much darker.
The result of tweaking the white values to an extreme can be seen in the image to the left titled "Highlights RGB". Note if you shifted this point up versus to the right reversing the values "Output: 187" and "Input: 255" the highlights would become much darker versus much lighter.
Throwing a mid-tone value into an extreme placement will result in changes exemplified in the images titled "Dark Midtones (RGB)" and "Light Midtones (RGB)" to the left.
Making minor changes in Curves can really enhance an image. This powerful function allows you to set accurate values for true black and even fine tune how much shadow detail is in an image. Inversely it also allows you to set accurate values for true white and even fine tune how much highlight detail is in an image. Once you get the hang of Levels & Curves adjustments you'll quickly notice uncorrected images and their diminished impact.
The final results of adjusting Levels and Curves in this example can
be seen in the Before & After image to the left. On the left of
this image is the Before (no Levels or Curves Adjustments)
and on the right is the After (with Levels & Curves Adjustments).