Processing RAW images - Stage 2 - Curves, Sharpening and HSL

After making the "Basic" adjustments in Adobe Camera Raw you can move to the next three tools: curves, details and HSL (hue/saturation/lightness).

You may choose to do these adjustments in Adobe Camera Raw or you may decide that you prefer to do them in Photoshop. My preference is to make the initial adjustments in Adobe Camera Raw and then do some fine tuning in Photoshop.

Something to keep in mind is that if you make these adjustments in Adobe Camera Raw they will be appplied to the whole image. If you make them in Photoshop you can use adjustment layers and masks to limit the effects to selected parts of the image. (Note:In CS4 you can localise some of these adjustments by using the "adjustment brush".)

When you select the "Curves" tab you are presented with a histogram that looks something like the histogram you see when you select the "curves" adjustment in Photoshop.The difference is that here you can select between two ways of adjusting the curve - "parametric" and "point".

Just as in Photoshop, the horizontal axis of the curves display represents the "input" (the starting image) and the vertical axis represents the "output" (what you get afer the adjustment). The straight diagonal line in the above image means that the "output" is the same as the "input" - there has been no adjustment.

In the "parametric" view you can adjust sections of the tone curve (highlights, lights, darks, shadows) within predefined limits to either lighten or darken those tonal ranges in the image.

Just pick the section of the curve you want to adjust and move the slider to the right to lighten those tones or to the left to darken those tones.

You will find that there is an automatic limit on how far you can take these adjustments.

You can click and drag the three triangles at the bottom of the tone curve to adjust the limits on the four "zones of adjustment". Again, there are automatic limits on how far you can take these adjustments.

When you select the "point" view the tonal curve is adjusted in much the same way as the "curves"' adjustment in Photoshop. You click on the diagonal line to establish control points and then click and drag to move those points.

You can select "preset" adjustments by clicking on the double-headed arrow on the right-hand end of the "curve" preset window. The default preset is "medium contrast" - this gives a slight lightening of the upper half of the tonal range and a slight darkening of the lower half of the tonal range.

When you select a different preset ("strong contrast" in this example) the curve will change.

Notice that the new curve automatically has several adjustment points on it.

After you make this preset adjustment you can click on one of the points on the curve and move that point - this will change the preset to "custom".

On any part of the curve where you make it "steeper" you will increase the contrast in that tonal range. On any part of the curve that you make "flatter" you will decrease the contrast in that tonal range.

Sharpening and noise reduction adjustments are accessed through the "detail" tab.

NOTE: You need to zoom to 100% (or higher) to see the effects of the adjustments that you make with the controls in this panel.

The default values are those shown in the above screen grab. The following images show the effect of applying these defaults to a RAW image.

The top image has no sharpening applied. The bottom image has the Adobe Camera Raw default sharpening applied. The difference is subtle but noticeable.

The next image shows the result of applying an "amount" of sharpening of 100.

To understand how the sliders work, you need to undestand that sharpening (here and in Photoshop) is really just an exaggeration of contrast along "edges" created by changes in brightness. This is illustrated in the the following images.

The transition between the two shades of grey represents an "edge" that would be identified by the sharpening control.

The left hand image has no sharpening applied.

The right hand image has shaprening applied. On the lighter side of the edge some of the pixels have been made even lighter. On the darker side of the edge some of the pixels have been made even darker. The result is the illusion of a sharper edge.

In Adobe Camera Raw the sharpening adjustment sliders have the following effects:

The "amount" slider varies the amount of lightening and darkening at the "edges".
The "radius" slider varies the width of this lightening/darkening.
The "details" slider controls the difference that there needs to be between lightness/darkness before a part of the image is identified as an "edge" that should be sharpened.

TIP: If you hold down the "Alt" key as you move the amount, radius or detail sliders the image will change to grayscale and the effects of the adjustments will be much easier to see. This will not work unless the image size is at 100% or higher.

Often you will want to sharpen parts of an image (the main subject) but not other parts (the background). In Adobe Camera Raw you can do this with the "masking" slider. You do it as follows:

Make sure the size of the image is at 100% or higher (otherwise you will not see the effect).
Adjust the sharpness sliders (amount, radius, detail) paying attention to the part of the image that you want sharpened.
Hold down the "Alt" key, click on the "Masking" slider and move it to the right. As you do, parts of the image will appear white (they are being sharpened) and parts of the image will appear black (they are not being sharpened). When the sharpening is being applied in the areas that you want, release the mouse.

This is the effect you will see when using the "masking" slider as described above.

Adobe Camera Raw does not have a "before and after" check box but you can toggle between your custom sharpening settings and the default settings as follows:

1. Make you sharpening adjustments. ACR will treat these as your "custom settings".
2. At the top right of the sharpening sliders (near the word "Detail") there is a small symbol that lets you select a pop-up menu from which you can select the "Camera Raw Defaults".
To toggle back to your custom settings just select the pop-up menu again and then select "Custom Settings".

TIP: You can use the same technique to toggle between the defaults and your custom settings from any of the adjustment windows (Basic, Tone Curve, etc).

By selecting one of the three tabs you can do the following:

HUE: The sliders allow you to adjust the the selected colour. For example, moving the blue slider changes only the blues in the image.

SATURATION: The sliders allow you to adjust the saturation (vividness) of the selected colour.

LUMINANCE: The sliders allow you to adjust the brightness of the selected colour.

If you make adjustments and then click on "default" all the sliders will return to zero.

If you double-click on any slider it will return that slider to zero without changing any of the other sliders.

If you click on the "Convert to Grayscale" box the image will change to monochrome and the sliders for the various colours will move to values that are automatically calculated by Adobe Camera Raw. This approach to monochrome conversion will be dealt with in more detail in another tutorial.

A couple of simple adjustments of the "Hue" sliders changed the image on the left to the image on the right.

Some simple adjustments of saturation and luminance changed the image on the left to the one on the right. Notice in particular how the detail in the concrete has increased.

The four tools on the right hand side are for split-toning, lens corrections, camera calibration and presets . They will be the subject of a later tutorial.

Comments and suggestions about this tutorial are welcome. Either leave them on this web site or email me at roykillen@mac.com

Roy Killen
Updated 17th April 2009