Histogram

A histogram is a handy tool that provides information about the distribution of colors in an image, in other words, displays its tonal range. The image tones can range from pure black on the left edge to pure white on the right edge of the histogram. So, what you have to pay attention to if you want to learn how to read a color histogram is the shape of the graph and where the peaks of the graph are.

Put simply, the higher the graph is at a given point, the more of a certain tone there is in an image. Therefore, considerably dark images with lower exposure and a lot of shadows will have a graph that peaks on the left side, while brighter images will have a histogram that is higher on the right side.

iPhone and iPad

Show or hide the histogram

1. Tap Color Adjustments in the toolbar.

2. If the histogram isn't visible, tap More at the top of the Color Adjustments pane (or at the bottom if you're using iPad) and tap Histogram.

3. Choose how to display the histogram:

   • Auto-hide — Automatically hides or shows the histogram when switching between presets and color adjustments.

   • Visible — Displays histogram at all times at the top of the Color Adjustments pane.

   • Hidden — Turns the histogram off.

4. Choose the histogram type:

   • RGB — An RGB histogram shows you all the tones in your image, from pure black on the left edge to pure white on the right edge of the histogram. The higher the graph is at a given point, the more of the tone is in the image. Therefore, a fairly dark image with lots of shadows will have a histogram that is higher on the left side (the shadows), while a fairly bright image will have a histogram that is higher on the right side (the highlights). The reason the histogram is known as an RGB histogram is that digital images are composed of a mix of three colors — red, green, and blue. These are used to create every other color.

   • Luminance — The luminance histogram displays the perceived brightness of an image. It doesn’t look at the individual color channels but at the colors themselves. So, unlike in the RGB histogram, pure blue will not be at the far right edge of the luminance histogram. And the luminance histogram also takes into account the fact that the human eye perceives green light as naturally brighter than red or blue. So any pure green areas will show up further right than pure blue or pure red areas.

On-canvas histogram controls

Once the histogram is turned on, you can tap it to find quick controls for switching between different histogram types, or hiding the histogram.

Switch histogram types: Tap the histogram and choose RGB or Luminance to quickly change the histogram type.

Turn histogram off: If you're no longer using the histogram, you can tap it and choose Hide Histogram to turn it off.

Move the histogram: You easily drag and drop the histogram to snap it to either corner of the screen.

Mac

Show or hide the histogram

1. Click Color Adjustments in the toolbar.

2. If the histogram isn't visible, click More at the bottom of the Color Adjustments pane and choose Histogram.

3. Choose how to display the histogram:

   • Automatically show histogram — Automatically hides or shows the histogram when switching between presets and color adjustments.

   • Always show histogram — Displays histogram at all times at the top of the Color Adjustments pane.

   • Hide histogram — Turns the histogram off.

4. Choose the histogram type:

   • RGB — An RGB histogram shows you all the tones in your image, from pure black on the left edge to pure white on the right edge of the histogram. The higher the graph is at a given point, the more of the tone is in the image. Therefore, a fairly dark image with lots of shadows will have a histogram that is higher on the left side (the shadows), while a fairly bright image will have a histogram that is higher on the right side (the highlights). The reason the histogram is known as an RGB histogram is that digital images are composed of a mix of three colors — red, green, and blue. These are used to create every other color.

   • Luminance — The luminance histogram displays the perceived brightness of an image. It doesn’t look at the individual color channels but at the colors themselves. So, unlike in the RGB histogram, pure blue will not be at the far right edge of the luminance histogram. And the luminance histogram also takes into account the fact that the human eye perceives green light as naturally brighter than red or blue. So any pure green areas will show up further right than pure blue or pure red areas.

On-canvas histogram controls

Once the histogram is turned on, you can Control-click it to find quick controls for switching between different histogram types, or choosing how the histogram is displayed.

View RGB color values: Turn RGB Color Values option on or off to show or hide RGB color values when hovering over areas of your photo.

Switch histogram types: Control-click the histogram and choose RGB or Luminance to quickly change the histogram type.

Change histogram display settings: To quickly change how the histogram is displayed or hide it, you can Control-click it and choose a desired option.

Move the histogram: You can quickly drag and drop the histogram to either corner of the screen.