Without a doubt, Curves is the most powerful tool in Photoshop. You can do more with Curves than with any other tool in the application. Granted, it may take you a while to get used to the dialog box, but after you do, you’ll never want to use anything else to correct your images. In this section, you’ll take a look at how you can use Curves to do the following:
- Lighten or darken specific areas of an image—without having to make selections first
- Improve color and contrast with just a few clicks
- Bring out more image detail than you ever thought possible
The Curves Dialog Box
By now you should know that 8-bit images contain a total of 256 shades of gray. The Curves dialog box allows you to adjust each shade of gray independently—something you cannot do with Levels or any other adjustment tool in Photoshop. The grid that you see when you open the dialog is actually a chart that shows how much ink or light will be used in your image. The bottom gradient represents all 256 shades of gray in the image. The gradient on the left indicates how dark an area will become if a point on the curve is moved to a specific height. The diagonal line between the two gradients represents each shade of gray from 0 to 255 (from white to black)—and here’s the best part—it’s interactive. This means that you can create multiple points on the line (16 total) and move them up or down to make that specific area of the image darker or lighter.
The Curves dialog now also contains several new display options. At the bottom of the dialog, click the down-facing arrow to reveal these settings:
Show Amount Of As a print designer, I always choose Pigment/Ink % over Light (0–255). When I am editing images for print, I like to think in terms of ink rather than light. After all, I’m designing for print output, not screen display. The darker I make a portion of the image, the more ink will be used in that area when it is printed. Choosing this option makes the gradient bars flip the opposite way so that black is up and to the right. If you choose to use Curves in percentages as I do, always remind yourself that “up means darker” and “down means lighter.” Make that your Curves mantra.
Grid Options The buttons to the right allow you to choose how you’d like the grid displayed: in simple or detailed view. The default simple option displays the grid in quarter tone (25%) increments, whereas the more accurate detailed view uses 10% increments. I like to be as accurate as possible, so I usually keep this set to detailed view.
Channel Overlays Enabling this option displays a separate colored curve for each color channel that has been edited with Curves while you are currently editing the composite curve. If you haven’t made any Curves adjustments to the individual channels, then there is no need to enable this option. However, if you have applied adjustments to the individual channels, enabling this option allows you to compare them to the adjustments made to the composite curve.
Histogram If you enable this option, Photoshop displays the image’s histogram in gray behind the curve and the grid. Although it’s helpful to be able to refer to the histogram right in the Curves dialog, I find it annoying that—unlike the histogram in the Histogram palette—the Curves histogram does not update itself. I usually show the histogram in the Curves palette, but continue to refer to the Histogram palette in the background so I can see how each one of my adjustments is affecting my image.
Baseline With this option enabled, you can display the original diagonal line in gray behind the curve. This allows you to compare your curve adjustments to the original line that indicates no change, and determine how much of an adjustment you’ve made. It’s definitely a good idea to keep this option turned on at all times.
Intersection Line Enable this option to display an intersection line over the grid as you move a selected point on the curve. This can help you make more-precise movements, especially when the grid is set to detailed display.
Bringing Out the Detail
There is no better tool than Curves to bring out hidden detail in an image. By adding points along the curve in the areas you’d like to enhance, you can adjust the curve’s angle and bring out the hidden detail, and this can all be done without having to make any detailed selections beforehand. Let’s try it. Open any image that lacks contrast and may be hiding some detail. Then choose Image --> Adjustments --> Curves, or add a Curves adjustment layer. With the Curves dialog open, move the cursor over the area that you’d like to enhance in the photo. As you hover the cursor over the image and click, Photoshop displays a circle along the diagonal line that represents the corresponding gray value for that area in the image. Add a control point at either end of this area of the curve by F/Ctrl+clicking.
After you’ve added these two new points to the curve, select the topmost point and move it upward by using the up arrow key. Press Control/Ctrl+Tab to toggle to the lower point, and move it downward by using the down arrow key. Using the arrow keys instead of moving points with the mouse allows you to be more precise when making your adjustments. It also makes it easier to reposition a point if you’ve taken an adjustment too far. To move each point in larger increments, hold down Shift as you press the up or down arrow keys. Preview the area in the image window to determine how steep to make the curve. The steeper the angle, the more contrast that is added, and the more detail that is revealed. If the other areas in the image are changing drastically as a result of your Curves adjustment, add another point and straighten out the rest of the curve to match the original diagonal baseline.
Using Gray to Correct Color
The Curves dialog also contains a series of eyedroppers that behave exactly the same as the eyedroppers located in the Levels dialog. You can use these eyedroppers along with the Info palette to color-correct an image with just a few clicks. To identify a black, white, and gray point in the image, first change your Info palette to display grayscale values. Hover over the image and refer to the palette to find the approximate darkest and lightest areas. Where you click with the black point and white point eyedroppers determines the darkest and lightest areas of the photo and expands or limits the image’s overall dynamic range. You can increase contrast by clicking in the areas that you would like to push into the darkest or lightest values. Finally, clicking on a neutral gray point balances the image’s color. After the black, white, and gray points are set with the eyedroppers, you can then bring out detail in the image (if necessary) by using the curve adjustment method described in the previous section.
Correcting a Dark Image
The Curves dialog also gives you an incredible amount of tonal control. By simply adding and adjusting points along the curve, you can improve a dark, backlit image with amazing precision—without having to make any selections.
Open any dark or backlit image and choose Image --> Adjustments --> Curves, or add a Curves adjustment layer. With the Curves dialog open, move the cursor over the area that you’d like to lighten in the photo. As you drag the cursor over the image, Photoshop displays a circle along the diagonal line that represents the corresponding gray value for that area in the image. Add a control point to this area of the curve by F/Ctrl+clicking. Then use the down arrow key to move the point and lighten that area of the image. (Remember your curves mantra: Down means lighter or less ink). Preview the area in the image window to determine how far to lower the point on the curve.
The Black and White Point sliders located underneath the grid can be adjusted by clicking and dragging. You can use these sliders just as you would when working with the Black and White sliders in the Levels dialog. Doing so repositions the black and white points located at each end of the curve, and alters the overall dynamic range of the image.
Continue to add and move points along the curve for any image areas that need to be lightened. If necessary, points can be removed by simply dragging them off the curve. If the other areas in the image are changing drastically as a result of your Curves adjustment, add another point and straighten out the rest of the curve to match the original diagonal baseline. Sometimes your final curve adjustment can be pretty extreme.
Curves and Channels
For images that require much more precise color correction, the Curves dialog also allows you to apply adjustments on a per channel basis. This type of adjustment is commonly used to color-correct skin tone after converting the image to CMYK mode.
- Lighten or darken specific areas of an image—without having to make selections first
- Improve color and contrast with just a few clicks
- Bring out more image detail than you ever thought possible
The Curves Dialog Box
By now you should know that 8-bit images contain a total of 256 shades of gray. The Curves dialog box allows you to adjust each shade of gray independently—something you cannot do with Levels or any other adjustment tool in Photoshop. The grid that you see when you open the dialog is actually a chart that shows how much ink or light will be used in your image. The bottom gradient represents all 256 shades of gray in the image. The gradient on the left indicates how dark an area will become if a point on the curve is moved to a specific height. The diagonal line between the two gradients represents each shade of gray from 0 to 255 (from white to black)—and here’s the best part—it’s interactive. This means that you can create multiple points on the line (16 total) and move them up or down to make that specific area of the image darker or lighter.
The Curves dialog now also contains several new display options. At the bottom of the dialog, click the down-facing arrow to reveal these settings:
Show Amount Of As a print designer, I always choose Pigment/Ink % over Light (0–255). When I am editing images for print, I like to think in terms of ink rather than light. After all, I’m designing for print output, not screen display. The darker I make a portion of the image, the more ink will be used in that area when it is printed. Choosing this option makes the gradient bars flip the opposite way so that black is up and to the right. If you choose to use Curves in percentages as I do, always remind yourself that “up means darker” and “down means lighter.” Make that your Curves mantra.
Grid Options The buttons to the right allow you to choose how you’d like the grid displayed: in simple or detailed view. The default simple option displays the grid in quarter tone (25%) increments, whereas the more accurate detailed view uses 10% increments. I like to be as accurate as possible, so I usually keep this set to detailed view.
Channel Overlays Enabling this option displays a separate colored curve for each color channel that has been edited with Curves while you are currently editing the composite curve. If you haven’t made any Curves adjustments to the individual channels, then there is no need to enable this option. However, if you have applied adjustments to the individual channels, enabling this option allows you to compare them to the adjustments made to the composite curve.
Histogram If you enable this option, Photoshop displays the image’s histogram in gray behind the curve and the grid. Although it’s helpful to be able to refer to the histogram right in the Curves dialog, I find it annoying that—unlike the histogram in the Histogram palette—the Curves histogram does not update itself. I usually show the histogram in the Curves palette, but continue to refer to the Histogram palette in the background so I can see how each one of my adjustments is affecting my image.
Baseline With this option enabled, you can display the original diagonal line in gray behind the curve. This allows you to compare your curve adjustments to the original line that indicates no change, and determine how much of an adjustment you’ve made. It’s definitely a good idea to keep this option turned on at all times.
Intersection Line Enable this option to display an intersection line over the grid as you move a selected point on the curve. This can help you make more-precise movements, especially when the grid is set to detailed display.
Bringing Out the Detail
There is no better tool than Curves to bring out hidden detail in an image. By adding points along the curve in the areas you’d like to enhance, you can adjust the curve’s angle and bring out the hidden detail, and this can all be done without having to make any detailed selections beforehand. Let’s try it. Open any image that lacks contrast and may be hiding some detail. Then choose Image --> Adjustments --> Curves, or add a Curves adjustment layer. With the Curves dialog open, move the cursor over the area that you’d like to enhance in the photo. As you hover the cursor over the image and click, Photoshop displays a circle along the diagonal line that represents the corresponding gray value for that area in the image. Add a control point at either end of this area of the curve by F/Ctrl+clicking.
After you’ve added these two new points to the curve, select the topmost point and move it upward by using the up arrow key. Press Control/Ctrl+Tab to toggle to the lower point, and move it downward by using the down arrow key. Using the arrow keys instead of moving points with the mouse allows you to be more precise when making your adjustments. It also makes it easier to reposition a point if you’ve taken an adjustment too far. To move each point in larger increments, hold down Shift as you press the up or down arrow keys. Preview the area in the image window to determine how steep to make the curve. The steeper the angle, the more contrast that is added, and the more detail that is revealed. If the other areas in the image are changing drastically as a result of your Curves adjustment, add another point and straighten out the rest of the curve to match the original diagonal baseline.
Using Gray to Correct Color
The Curves dialog also contains a series of eyedroppers that behave exactly the same as the eyedroppers located in the Levels dialog. You can use these eyedroppers along with the Info palette to color-correct an image with just a few clicks. To identify a black, white, and gray point in the image, first change your Info palette to display grayscale values. Hover over the image and refer to the palette to find the approximate darkest and lightest areas. Where you click with the black point and white point eyedroppers determines the darkest and lightest areas of the photo and expands or limits the image’s overall dynamic range. You can increase contrast by clicking in the areas that you would like to push into the darkest or lightest values. Finally, clicking on a neutral gray point balances the image’s color. After the black, white, and gray points are set with the eyedroppers, you can then bring out detail in the image (if necessary) by using the curve adjustment method described in the previous section.
Correcting a Dark Image
The Curves dialog also gives you an incredible amount of tonal control. By simply adding and adjusting points along the curve, you can improve a dark, backlit image with amazing precision—without having to make any selections.
Open any dark or backlit image and choose Image --> Adjustments --> Curves, or add a Curves adjustment layer. With the Curves dialog open, move the cursor over the area that you’d like to lighten in the photo. As you drag the cursor over the image, Photoshop displays a circle along the diagonal line that represents the corresponding gray value for that area in the image. Add a control point to this area of the curve by F/Ctrl+clicking. Then use the down arrow key to move the point and lighten that area of the image. (Remember your curves mantra: Down means lighter or less ink). Preview the area in the image window to determine how far to lower the point on the curve.
The Black and White Point sliders located underneath the grid can be adjusted by clicking and dragging. You can use these sliders just as you would when working with the Black and White sliders in the Levels dialog. Doing so repositions the black and white points located at each end of the curve, and alters the overall dynamic range of the image.
Continue to add and move points along the curve for any image areas that need to be lightened. If necessary, points can be removed by simply dragging them off the curve. If the other areas in the image are changing drastically as a result of your Curves adjustment, add another point and straighten out the rest of the curve to match the original diagonal baseline. Sometimes your final curve adjustment can be pretty extreme.
Curves and Channels
For images that require much more precise color correction, the Curves dialog also allows you to apply adjustments on a per channel basis. This type of adjustment is commonly used to color-correct skin tone after converting the image to CMYK mode.
Curves
![Curves]()
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