Photoshop - Adjust Contrast Using Levels

Here are two images,
The first doesn't have enough contrast and the second has too much contrast.

We can adjust this using the Levels tool in Photoshop.

Open the first image in Photoshop.

Go to Image > Adjustments > Levels

We are going to set the parameters for how bright and dark we want the brightest and darkest parts of our image to be.

 In the Levels pop-up, double click on the white eyedropper which is the one to the right.

 In the box which pops up, enter the value 245 for each of RG and B.

We are telling photoshop that we don't want white to be totally white when our image prints.

Click OK

 In the Levels pop-up, double click on the black eyedropper which is the one to the left.

In the box which pops up, enter the value 10 for each of RG and B.

We are telling Photoshop that we don'y want the black part of our image to completely black, we want to see some detail.
Click OK.

Click OK in the Levels pop-up window and when asked if you want to save these changes, say Yes.



Now at the bottom of the Layers panel, click add a New Adjustment Layer (it looks like a half moon) and choose Threshold.

The Threshold dialogue box will pop up.

Drag the handle in the Threshold window all the way to the right.

 Your desktop will now be showing you the brightest parts of the image.

Select the eyedropper tool and hold it over one these white areas.

Hold down the Shift Key and Left Click.

You will see that a little number one has been placed to mark this bright spot.

Now move the handle in the Threshold pop-up all the way to the left. If the image is all white, move the handle gradually to the right until some black begins to appear.

Now select the eyedropper again. Hold it over one of the black areas, press the Shift Key and Left Click.

This area has been marked with a number 2.

Now that we have these markers we can delete the Threshold Layer.

Right Click in the layer and click Delete layer

Now back at the bottom of the Layers Window, click Add New Adjustment Layer again and select Levels.

In the Levels dialogue box which pops up, select the white eyedropper and click in the Number 1 target in your photo to adjust the highlights of the image.

Now select the black eyedropper and click in the Number 2 target to adjust the shadow in your image.

You should see that your image now has much more contrast.

You can adjust the mid-tones of your image by moving the central handle in the levels pop-up. 

To delete the number targets from your image, select the Colour Sampler tool from the Tool Bar and in the control panel click clear.

These handles won't appear in your printed image if you don't delete them.

Photoshop - What the blending modes do

This handy description of what the blending modes do in Adobe products comes from

http://helpx.adobe.com/en/photoshop/using/blending-modes.html

Blending mode descriptions

Choose from the Mode pop‑up menu in the options bar.

Note:

Only the Normal, Dissolve, Darken, Multiply, Lighten, Linear Dodge (Add), Difference, Hue, Saturation, Color, Luminosity, Lighter Color, and Darker Color blending modes are available for 32‑bit images.

Normal

Edits or paints each pixel to make it the result color. This is the default mode. (Normal mode is called Threshold when you’re working with a bitmapped or indexed-color image.)

Dissolve

Edits or paints each pixel to make it the result color. However, the result color is a random replacement of the pixels with the base color or the blend color, depending on the opacity at any pixel location.

Behind

Edits or paints only on the transparent part of a layer. This mode works only in layers with Lock Transparency deselected and is analogous to painting on the back of transparent areas on a sheet of acetate.

Clear

Edits or paints each pixel and makes it transparent. This mode is available for the Shape tools (when fill region  is selected), Paint Bucket tool , Brush tool , Pencil tool , Fill command, and Stroke command. You must be in a layer with Lock Transparency deselected to use this mode.

Darken

Looks at the color information in each channel and selects the base or blend color—whichever is darker—as the result color. Pixels lighter than the blend color are replaced, and pixels darker than the blend color do not change.

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.

Color Burn

Looks at the color information in each channel and darkens the base color to reflect the blend color by increasing the contrast between the two. Blending with white produces no change.

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.

Lighten

Looks at the color information in each channel and selects the base or blend color—whichever is lighter—as the result color. Pixels darker than the blend color are replaced, and pixels lighter than the blend color do not change.

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.

Color Dodge

Looks at the color information in each channel and brightens the base color to reflect the blend color by decreasing contrast between the two. Blending with black produces no change.

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.

Overlay

Multiplies or screens the colors, depending on the base color. Patterns or colors overlay the existing pixels while preserving the highlights and shadows of the base color. The base color is not replaced, but mixed with the blend color to reflect the lightness or darkness of the original color.

Soft Light

Darkens or lightens the colors, depending on the blend color. The effect is similar to shining a diffused spotlight on the image. If the blend color (light source) is lighter than 50% gray, the image is lightened as if it were dodged. If the blend color is darker than 50% gray, the image is darkened as if it were burned in. Painting with pure black or white produces a distinctly darker or lighter area, but does not result in pure black or white.

Hard Light

Multiplies or screens the colors, depending on the blend color. The effect is similar to shining a harsh spotlight on the image. If the blend color (light source) is lighter than 50% gray, the image is lightened, as if it were screened. This is useful for adding highlights to an image. If the blend color is darker than 50% gray, the image is darkened, as if it were multiplied. This is useful for adding shadows to an image. Painting with pure black or white results in pure black or white.

Vivid Light

Burns or dodges the colors by increasing or decreasing the contrast, depending on the blend color. If the blend color (light source) is lighter than 50% gray, the image is lightened by decreasing the contrast. If the blend color is darker than 50% gray, the image is darkened by increasing the contrast.

Linear Light

Burns or dodges the colors by decreasing or increasing the brightness, depending on the blend color. If the blend color (light source) is lighter than 50% gray, the image is lightened by increasing the brightness. If the blend color is darker than 50% gray, the image is darkened by decreasing the brightness.

Pin Light

Replaces the colors, depending on the blend color. If the blend color (light source) is lighter than 50% gray, pixels darker than the blend color are replaced, and pixels lighter than the blend color do not change. If the blend color is darker than 50% gray, pixels lighter than the blend color are replaced, and pixels darker than the blend color do not change. This is useful for adding special effects to an image.

Hard Mix

Adds the red, green and blue channel values of the blend color to the RGB values of the base color. If the resulting sum for a channel is 255 or greater, it receives a value of 255; if less than 255, a value of 0. Therefore, all blended pixels have red, green, and blue channel values of either 0 or 255. This changes all pixels to primary additive colors (red, green, or blue), white, or black.

Note:

For CMYK images, Hard Mix changes all pixels to the primary subtractive colors (cyan, yellow, or magenta), white, or black. The maximum color value is 100.

Difference

Looks at the color information in each channel and subtracts either the blend color from the base color or the base color from the blend color, depending on which has the greater brightness value. Blending with white inverts the base color values; blending with black produces no change.

Exclusion

Creates an effect similar to but lower in contrast than the Difference mode. Blending with white inverts the base color values. Blending with black produces no change.

Subtract

Looks at the color information in each channel and subtracts the blend color from the base color. In 8- and 16-bit images, any resulting negative values are clipped to zero.

Divide

Looks at the color information in each channel and divides the blend color from the base color.

Hue

Creates a result color with the luminance and saturation of the base color and the hue of the blend color.

Saturation

Creates a result color with the luminance and hue of the base color and the saturation of the blend color. Painting with this mode in an area with no (0) saturation (gray) causes no change.

Color

Creates a result color with the luminance of the base color and the hue and saturation of the blend color. This preserves the gray levels in the image and is useful for coloring monochrome images and for tinting color images.

Luminosity

Creates a result color with the hue and saturation of the base color and the luminance of the blend color. This mode creates the inverse effect of Color mode.

Lighter Color

Compares the total of all channel values for the blend and base color and displays the higher value color. Lighter Color does not produce a third color, which can result from the Lighten blend, because it chooses the highest channel values from both the base and blend color to create the result color.

Darker Color

Compares the total of all channel values for the blend and base color and displays the lower value color. Darker Color does not produce a third color, which can result from the Darken blend, because it chooses the lowest channel values from both the base and the blend color to create the result color.