How to Read a Photoshop Histogram

Member

By e-Rambler
User-Submitted Article

Article Rating:

(3 Ratings)

Photoshop histogram

All Photoshop include a histogram tool that gives us information on the image in the editing process. In fact, histogram is so valuable that most graphic programs include it. So what does it do? It is a graph that shows user the current "tonal range" of an image. Tonal range is the brightness/darkness values of the image. By reading the tonal values, a user can determine the contrast and sharpness of an image, which is very useful in image editing.

Difficulty: Moderately Easy

Instructions

Things You'll Need:

Adobe Photoshop, any edition
PC Windows XP / Vista O.S.

Step 1

Photoshop histogram

Open your Photoshop and load an image. Go to the main menu Image > Histogram.

In this view, it will show you the overall information on a graph about the image you just opened (or looking at/editing), which appears like an undersea mountain range.
Step 2

Photoshop histogram

From the small triangle indicators below the graph, you can know which tone region your current image falls in. The tonal value reads from the darkest to the left, and the brightest to the right on the graph.
Step 3

Channel menu

There are different channels you can choose to see the different tonal values of your image. Click on the down fly-out arrow beside the Channel box near the top left of the dialog window. Choose any items on the list and a more detailed histogram will show, according to the item you picked.
Step 4

Screenshot composit showing different histogram channels

After choosing your choice of channel, you should see one of these in the histogram. This is a composite image of different Photoshop histogram screenshots showing separate channels and information.
Step 5

Histogram of select image area

Previous instructions are for viewing the whole image. You can also choose just to see a select area on the image that you want information on.

To do this, select the Rectangular Marquee tool on your tool box, then drag by holding down your left mouse key on the image area. Release mouse key, while the select area is active, go to Image > Histogram. The select area information will show.
Step 6

Read histogram

Now into reading the histogram. The horizontal axis (x) is the brightness value for pixels. As mentioned before, the darkest possible color (black, value 0) is to the left and the brightest color (white, value 255) is on the right. Then the vertical scale (y) shows the approximate number of pixels in the current image having the tone value that relates to that position on the horizontal axis.

This is also notable - - both axis scales are compressed to fit within the available viewing screen or window; meaning each user will see a slight change on the scale and pixel position depending on the size of their screen or window. However, the total information given about an image is all the same, despite the size of the window or screen size difference. It is just a matter of how much space the histogram could be fit in into a certain given area on a screen/window.
Step 7

Reading a histogram is easy, and sadly it is often underused. The histogram is just a simple bar chart but an important tool to anyone who is serious about their photographs and images. The Photoshop histogram can be put to good use if you wish to produce high contrast and sharp images. You can then edit your image according to the histogram read instead of relying just on your eyes to judge the image.

Check out more on how to use the Photoshop histogram via links in the "Resources" section below.