Paper title: DSDN144 Digital Photographics

Exercise: Experimenting with Curves

Note that this is simply an experimentation exercise to get you to understand how Curves work. Complete the Levels exercise before doing this.

1. Select the File and go to New (or press Control + N). Create a new file

600 pixels wide by 450 pixels high, resolution at 72 pixels/inch, RGB with

a white background. Click OK.

2. Press D on the keyboard to set the foreground and background colours

in toolbox to black and white. This is the default setting.

3. Select the Gradient tool (or press G on the keyboard).

4. In the options (below menu) click on the drop down arrow on the Gradient Picker to open it. Make sure the Foreground to Background gradient is

selected (if you are not sure which is which, position your pointer over

each gradient to see the tooltip description).

5. To make your gradient linear, select the first of the group of five icons to

the right of the Gradient Picker.

6. In the Gradient options palette, set Mode to Normal and Opacity to

100%, make sure Dither and Transparency are ticked but Reverse is

not.

7. Hold down the Shift key (in order to your gradient perpendicular) and

starting at the left of the image, drag your pointer right over to the right

side. This will create a gradient from black to white (0 to 255).

8. If no rulers are showing on your image press Control + R.

9. Select the Move tool, position your pointer on top of the horizontal ruler,

click and drag a guide half way down your image.

10. Using the Rectangular Marquee tool, select the top half of your image.

The bottom of your marquee should snap to the halfway mark guide.

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11. From the Image menu select Adjustments then Posterise (second from

the bottom of the list). Make sure that Preview is ticked and type some

different numbers in the Levels box to observe their effect. Lastly type in

9 and click OK.

The tonal range of the top section of the gradient is reduced from 256 levels to

just nine. You will now adjust the tonal characteristics using Levels and Curves

and it will be easier to identify and measure the changes than with the portion of

the image that has retained 256 levels.

12. Click on the Create New Fill or Adjustment Layer button on the bottom

of the Layers Palette (fourth icon along - black and white circle). Select

Curves. The Curves dialogue box will come up.

13. Click on the diagonal line to add an adjustment point. Click and drag this

adjustment point to create a curve. Adding additional points to the line

allows a variety of different shaped curves to be created.

14. Try to create an ‘S’ shaped curve using two adjustment points. Observe

the effects on both the step wedge and the gradient.

15. Press the Alt key and click Reset in the Curves box to return the curve to

its original setting.

16. Move the pointer to different tones on the stepped part of your image and

click and hold to observe the corresponding points that these tones

occupy on the curves scale. Select a point on the curve that corresponds

to a shadow tone, e.g. tone 3.

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17. Click on the curve to select a light highlight tone (tone 7). Move this point

up or down to lighten or darken your selected highlight. You will notice

that the shadow tone adjustment point is effectively anchored and will not

move. This technique of isolating tones that are not to be adjusted is

called ‘pegging’. If you click on the highlight adjustment point you can

observe the change of level in the output box at the bottom left-hand

corner of curves dialogue box.

18. Open the Houses image in the Curves Exercise folder in the DSDN144

Course Material folder. Bring up a Curves Adjustment Layer to

experimenting with the technique of pegging.

19. Cancel out of the Curves Adjustment Layer dialogue box and with the

Marquee tool select a middle portion of the image.

20. Once again, using a Curves Adjustment Layer, experiment with pegging.

This time you will be able to see the effect in relation to the image’s

original tones.

21. Once you have finished this, open the Nightshot image in the same

folder.

22. Create a Curves Adjustment Layer. Adjust the curve so that the dome

and the sky are brighter (do not worry if other areas of the picture blow

out). Click OK.

23. Notice how the foreground and background colours on the toolbox change

to black and white. When an Adjustment Layer is created a mask is

automatically created with it.

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24. Using the Paintbrush tool, paint with black on the image where the picture

has blown out. Notice how the tone returns to the image – you are

creating a mask so that the curves adjustment does not affect that area of

the image.

25. Press X on the keyboard and paint over the area where you painted black

before. You have now wiped away the mask.

26. Paint with black again but this time change the opacity of the Paintbrush.

27. Keep experimenting; adding and subtracting the mask and varying opacity

until you are happy with your image.

28. Once you have finished, you can see how your image looks before and

after your adjustments by clicking the Eye icon to the left of the adjustment

layer on and off.