Image Contrast and Tonal Range Tweaks Part 1 by Robert Amoruso

[Robert Amoruso]

Image Contrast and Tonal Range Tweaks
By Robert Amoruso

Below are some of the methods I use to tweak my images to improve tonal relationships. In my critiques I refer to them often so instead of repeating myself, will be referring here.

Comments welcome and if you see anything that needs correction, etc, please let me know.

Part 2 can be found at http://www.birdphotographers.net/for...d.php?p=161168.

Reverse S-Curve

Using Photoshop CS3 (other programs with curve adjustments can be used).



This is a reverse of the traditional S-Curve used to add contrast to an image. Here the Reverse S-Curve will lower contrast. Sometimes after I use this, it will make the image look flat. I will correct that flatness using a Selective Color adjustment (next section) or the Shadows/Highlights adjustment and add mid-tone contrast using the slider near the bottom (next section).

Set the blending mode to "Luminosity" so as to influence the tonal relationships but not the color.


Selective Color (Photoshop)

Use Selective Color to add punch to an image (learned this one from Artie Morris).



Left Image: Adding BLACK to Black color channel.
Right Image: Adding BLACK to Neutral color channel.

This adds black to the neutrals and blacks in the image. It adds punch and is a good all around tweak but when using a Reverse S-Curve, it can add some punch lost by this curve correction. Generally 2 to 5 is all you need.

Shadows/Highlights Adjustment (Photoshop)

This control is part of Photoshop (CS2 and above).



Use the Midtone Contrast slider to enhance midtones in the image. After doing a shadow correction, midtones can look flat and this will help to correct them.

Local Contrast Enhancement (LCE) (Photoshop)

You probably have used Photoshop’s Unsharp Mask (USM) filter to sharpen your images. However, you can use it to increase the local contrast (unlike a curves adjustment which is more global and flattens shadows and highlights in an attempt to increase contrast in the mid-tones). The trick here is too increase the local contrast in small regions of tonal differences and protect large-scale tonal relationships in the shadows and highlights.

This is done using a BG copy and setting the USM amount low, radius high and threshold to zero.

Try these settings on a BG copy using USM (Filter > Sharpen > Unsharp Mask)

• Amount — 20%
• Radius — 50
• Threshold — 0

Definitions:

• Amount is the amount by which small scale differences are increased. Think of it as the contrast increase. More percentage = more contrast.
• The Radius setting is the division between the small scale and large scale contrast differences. A smaller radius enhances smaller-scale detail. Range is generally 30 to 100 pixels.
• Threshold is set at zero to reduce artifacts. Higher settings may enhance contrast only along the most prominent edges.

EXPERIMENT! I can show you examples, but try it out on your images. Use CTRL + Z to undo it. Use the History Palette to toggle back and forth to see the difference.

The example below demonstrates the technique using the settings above.



Besides enhancing local contrast; fog, flare and other contrast lessening affects can be minimized or eliminated using LCE. I use it to cut through fog to bring detail into obscured backgrounds. By changing the settings, you can varying the fog eliminating affect.


Blending Modes (Photoshop)

Blending Modes can be applied to a background (BG) copy or an adjustment layer. The four I use most are listed below. Artie just recently popularized his use of the Linear Burn BM. I use it occasionally but the one you will find most useful is the Multiply BM.

Blending Mode Descriptions (from PSCS3 Help)

1. To Darken an Image
   
   • Multiply looks at the color information in each channel and multiplies the base color by the blend color. The result color is always a darker color. Multiplying any color with black produces black. Multiplying any color with white leaves the color unchanged. When you’re painting with a color other than black or white, successive strokes with a painting tool produce progressively darker colors. The effect is similar to drawing on the image with multiple marking pens.
   • Linear Burn looks at the color information in each channel and darkens the base color to reflect the blend color by decreasing the brightness. Blending with white produces no change.
   
   
2. To Lighten an Image
   
   • Screen looks at each channel’s color information and multiplies the inverse of the blend and base colors. The result color is always a lighter color. Screening with black leaves the color unchanged. Screening with white produces white. The effect is similar to projecting multiple photographic slides on top of each other.
   • Linear Dodge (Add) looks at the color information in each channel and brightens the base color to reflect the blend color by increasing the brightness. Blending with black produces no change.
   
   
3. 3. Definitions
   
   • The base color is the original color in the image.
   • The blend color is the color being applied with the painting or editing tool.
   • The result color is the color resulting from the blend.
   
   

Blending Mode Methods

1. Method 1 – Blending Modes using a Background Copy (BG)
   
   • In lieu of a curves adjustment you can create a blending layer from a BG copy of the image and change the blending mode to one of the following. Descriptions from Photoshop Help.
   • Layers palette with a Background Copy’s Blending Mode changed to Multiply is shown below.
   • What's Happening
     
     • In the Multiply mode you are using the BG as the blend color and multiplying the base color with the blend color. The affect is the color is darkened. The reverse occurs with the Screen Mode.
     • In lieu of using a background copy (BG), you can select the areas you wish to apply the blending mode or curves adjustment to as described in Method 2.
     
     
   
   
2. Method 2 – Selecting Highlights and using Blending Modes.
   
   • Method 2A
     
     • Select a BG copy w/o any modifications.
     • Hit CTRL + ALT + ~ (~ is the tilde symbol).
     • This creates a feathered selection.
     • Hit CTRL + J to create a new layer of the selection.
     • Add a vector mask (bottom of layer palette look for the camera icon and click it).
     • Change your blending mode as required.
     
     
   • Method 2B
     
     • Select the channels palette,
     • While holding down the CTRL key, double click on the RGB channel.
     • This creates a feathered selection (see below).
     • Hit CTRL + J to create a new layer of the selection.
     • Add a vector mask (bottom of layer palette look for the camera icon and click it).
     • Change your blending mode as required.
     
     
   
   
   
   • The above two methods select the highlights, but what about the shadows?
     
     • After making the selection above hit SHIFT + CTRL + I to inverse the selection.
     • Now you have the shadows selected and can continue with the steps above.
     
     
   
   

See the following sections in Part 2 on making selections and gradient masks and how they tie into Blending Modes in more detail.

Part 2 can be found at http://www.birdphotographers.net/for...d.php?p=161168.

 


More to come.