Photoshop contains two palettes that are essential to color correction: the Histogram palette and the Info palette. The information provided in these two palettes can be used hand in hand with the Curves and Levels dialog boxes to help guide your corrections.
Histogram Palette
The Histogram palette displays a simple bar graph called a histogram. It contains 256 bars (from 0 to 255—yes, zero counts in this instance) that vary in width and height to show the distribution of colors or tonal information in an image. Each bar represents one brightness value from black (on the far left) to white (on the far right). The height of each bar represents the number of pixels that correspond to that brightness value. The histogram palette helps you “see into” the image and locate where the darkest colors begin in each color channel and where the lightest colors end.
The histogram can tell you things about your image at a glance. For example, if your image contains clipped highlights, the bars will spike at the right end of the histogram. If it contains clipped shadows, the bars will spike at the left end. An image that contains a limited dynamic range will produce a histogram with a clump of bars in the middle and nothing at either end. If the histogram displays gaps between bars, it means that the image has already been edited and some data has been lost. Agood histogram should fill the entire tonal range and contain smooth contours rather than obvious spikes.
The Histogram palette can help you monitor your adjustments—especially when working with Curves—so that you don’t take them too far and wind up harming your image. The palette displays “before and after” information that can be very helpful. As you start to adjust your image, the palette overlays a histogram representing the image’s current state (black) with another histogram representing what the image looked like before you starting adjusting it (gray). One thing to keep in mind when working with the Histogram palette is not to fixate on the histogram alone. There is no such thing as a perfect histogram, and often really good images can have “ugly” histograms. For example, some images are supposed to have pure white and pure black areas, such as a product shot placed over a pure white background, or an image captured at night. The histogram for these types of images should display a tall spike at either end, indicating that there is a lack of detail in the white or black areas—which is perfectly fine. Remember—fixing the histogram does not always fix the image. The Histogram palette can provide information to help you make your adjustments. As you’re using it, make sure to focus on the image and not worry so much about the “ugliness” of the histogram.
Info Palette
The values displayed in the Info palette can be extremely helpful when making adjustments, especially when using Curves or Levels. Unlike the Histogram palette, which provides overall tonal information, the Info palette allows you to analyze specific points in an image. If you move the cursor over a specific area of the photo, the Info palette displays the precise pixel values and exact location coordinates for that point in the image. If you make an adjustment, it also displays “before and after” information. The number on the left is the initial reading; the number on the right is the resulting value after making the adjustment.
The Palette Options dialog box (accessible from the palette menu) allows you to set up exactly what information you’d like displayed. To compare conversion values for print graphics, you should display RGB values on one side of the palette and CMYK on the other. When working with the eyedroppers in Levels or Curves, you may want to set one side to Grayscale and one to RGB. Doing so can help you locate a neutral midpoint in the image. Be sure to choose 8-bit or 16-bit depending on the type of images you are editing. You can also change Info palette display settings from the pop-up menu by clicking any one of the small right-facing arrows located under the eyedropper and axis icons. The RGB and CMYK values displayed in the palette are calculated based on the Color Settings you’ve chosen in Preferences. Being able to see CMYK values in the Info palette as you edit an RGB image allows you to monitor your color for print before making the final conversion to CMYK.
Histogram Palette
The Histogram palette displays a simple bar graph called a histogram. It contains 256 bars (from 0 to 255—yes, zero counts in this instance) that vary in width and height to show the distribution of colors or tonal information in an image. Each bar represents one brightness value from black (on the far left) to white (on the far right). The height of each bar represents the number of pixels that correspond to that brightness value. The histogram palette helps you “see into” the image and locate where the darkest colors begin in each color channel and where the lightest colors end.
The histogram can tell you things about your image at a glance. For example, if your image contains clipped highlights, the bars will spike at the right end of the histogram. If it contains clipped shadows, the bars will spike at the left end. An image that contains a limited dynamic range will produce a histogram with a clump of bars in the middle and nothing at either end. If the histogram displays gaps between bars, it means that the image has already been edited and some data has been lost. Agood histogram should fill the entire tonal range and contain smooth contours rather than obvious spikes.
The Histogram palette can help you monitor your adjustments—especially when working with Curves—so that you don’t take them too far and wind up harming your image. The palette displays “before and after” information that can be very helpful. As you start to adjust your image, the palette overlays a histogram representing the image’s current state (black) with another histogram representing what the image looked like before you starting adjusting it (gray). One thing to keep in mind when working with the Histogram palette is not to fixate on the histogram alone. There is no such thing as a perfect histogram, and often really good images can have “ugly” histograms. For example, some images are supposed to have pure white and pure black areas, such as a product shot placed over a pure white background, or an image captured at night. The histogram for these types of images should display a tall spike at either end, indicating that there is a lack of detail in the white or black areas—which is perfectly fine. Remember—fixing the histogram does not always fix the image. The Histogram palette can provide information to help you make your adjustments. As you’re using it, make sure to focus on the image and not worry so much about the “ugliness” of the histogram.
Info Palette
The values displayed in the Info palette can be extremely helpful when making adjustments, especially when using Curves or Levels. Unlike the Histogram palette, which provides overall tonal information, the Info palette allows you to analyze specific points in an image. If you move the cursor over a specific area of the photo, the Info palette displays the precise pixel values and exact location coordinates for that point in the image. If you make an adjustment, it also displays “before and after” information. The number on the left is the initial reading; the number on the right is the resulting value after making the adjustment.
The Palette Options dialog box (accessible from the palette menu) allows you to set up exactly what information you’d like displayed. To compare conversion values for print graphics, you should display RGB values on one side of the palette and CMYK on the other. When working with the eyedroppers in Levels or Curves, you may want to set one side to Grayscale and one to RGB. Doing so can help you locate a neutral midpoint in the image. Be sure to choose 8-bit or 16-bit depending on the type of images you are editing. You can also change Info palette display settings from the pop-up menu by clicking any one of the small right-facing arrows located under the eyedropper and axis icons. The RGB and CMYK values displayed in the palette are calculated based on the Color Settings you’ve chosen in Preferences. Being able to see CMYK values in the Info palette as you edit an RGB image allows you to monitor your color for print before making the final conversion to CMYK.
Color Correction Tools
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