Level 3

Lesson 19

Learning how to make tonal adjustment and color adjustment to a flat image using the Curves command

Introduction

The following lesson will teach you how to adjust tonality and color to a flat image by using the Curves command.

·   Open an image file.

To help us understand the overall contrast in this image.

·   Go to the “Menu bar”.

·   Choose Window > Histogram

The lack of pixel values on either end of the histogram identifies the lack of contrast in both the highlights and the shadows.

This characteristic reflects that this is a flat image.

·   Go to the “Menu bar”.

·   Choose Image > Adjustments > Curves.

The “Curves” dialog box appears.

·   Check the “Preview” box so that we can see the effect of changes in the image.

·   Make sure that the dark end of the horizontal bar below the graph is on our left.

We will continue to work on the brightness mode.

·   Reposition the Document window, the Curves dialog box and the Histogram palette by dragging their title bars, so that we can see all of them simultaneously.

On the “Curves” dialog box:

By default, the Point tool is selected.

·   With this tool, click to add a control point to the midtones, a point to the 3/4 tones and a point to the 1/4 tones of the curve.

·   Drag the points at 1/4 tones and 3/4 tones in opposite directions to create an S-curve.

·   Adjust the shape of the curve while watching the effect on the image. Stop when we get the right effect.

Notice: Move up a point near the top of the curve will lighten highlights; move down a point near the bottom of the curve will darken shadows

·   Look at the “Histogram” palette.

The histogram updates to produce a more evenly distributed full tonal range.

·   Look at the “Document window”.

Brightness and contrast in the image is improved.

·   Go to the “Menu bar”.

·   Choose Window > Info.

·   Move the pointer from the Curves dialog box into the image. The pointer changes to an eyedropper.

·   Move the eyedropper around the leaves and note the values in the Info palette.

The Info palette displays the color value of the pixel beneath the pointer.

As shown, the B (blue) value is much higher than the G (green) value.

Notice: The reading in the left column is the original color value. The reading in the right column is the color value after adjustment is made.

·   Hold down Shift-Control and click once in the sample leaves area.

After that, a control point is added to all the three color channel curves.

·   From “Channel”, choose Blue.

The Input value 130 corresponds to the original B (blue) value shown in the Info palette.

·   In the Output text box, change 130 to 110 to decrease the amount of blue.

As we did that, the point moves down automatically, so does the curve.

·   Look at the “Document window”.

The image updates to reflect the modification.

Keep in mind that changing one color component will affect the other colors in an image. Therefore, to correct color balance we have to adjust more than one channel.

·   From “Channel”, choose Green.

In Step#12, a point has already been added to this channel curve.

The Input value 99 corresponds to the original G (green) value shown in the Info palette.

·   In the Output text box, change 99 to 118 to increase the amount of green in the image.

Notice that the point and the curve move up automatically.

·   Look at the “Document window”.

The image further updates showing an increase in green.

·   From “Channel”, choose Red.

In Step#12, a point has already been added to this channel curve.

The Input value 64 corresponds to the original R (red) value shown in the Info palette.

·   In the Output text box, change 64 to 88 to increase the amount of red in the image.

Again, the point and the curve move up automatically.

·   Look at the “Document window”.

The color balance of the image is corrected.

Conclusion

In this lesson, we learned that, drag a curve to an S-shape will increase contrast in an image.

We also learned to correct color balance by adjusting all the three color channel curves.