A histogram, You might have seen after you open Photoshop, using camera raw. Its a graph playing with color highlights and tones of an image. While it may be intimidating looking, histograms are nothing really all that complex. What they represent are the distribution of highlights & tones throughout the image just a simple algebraic graph, coming down to it.

A histogram illustrates the distribution of color tones and highlights at each color intensity level,

At the left part it shows the variations in shadows,Color mid tones at the center & Variations in highlights at the right.

Thus, The histogram gives a quick picture of the tonal range of the image, or the image key type. A low-key image has detail concentrated in the shadows; a high-key image has detail concentrated in the highlights; and an average-key image has detail concentrated in the mid tones.

a) HISTOGRAM PANEL OVERVIEW :

Choose Window > Histogram or click the Histogram tab to open the Histogram panel. By default, the Histogram panel opens in Compact View It has three other ones,

1. Expanded

2. Compact

3. All channels view

b) USING THE HISTOGRAM :

1. By default, the histogram displays the tonal range of the entire image. To display histogram data for a portion of the image,select that portion.

2. Choose Image > Histogram. The horizontal axis of the histogram represents the intensity values, or levels, from darkest (0) at the far left to brightest (255) at the far right; the vertical axis represents the total number of pixels with a given value.

3. To view information about a specific point on the histogram, place the pointer there. To view information about a range of values, drag in the histogram to highlight the range. Click OK when you are finished.

Note: The histogram for an adjustment layer reflects the data for all visible layers beneath it.

It is useful in making other corrections like,

a) Over-Exposure

b) Lost Data Spikes

c) Under-Exposed

The art & craft of images has been linked more with the digital now that has added to our creativity ! It is in fact a much more robust tool for making the color corrections & improving the quality of an image.