Digital Imaging

Week 6 Part II: Traditional Techniques & Alpha Channels

Lesson Objectives

At the end of this lesson students will be able to:

  • Convert colored images into black and white images in Adobe Photoshop
  • Use Channels with RGB colors
  • Be familiar with Channels beyond RGB colors

black and white photo of a man walking in a tunnel


In this week, there are 2 parts to the Exercise. First, we will turn a photograph into a Black and White image and use the Dodge and Burn tools to enhance it. In the second part, we will use the selection tools, such as Quick Selection and also Quick Mask Mode to make selections and store the information as an Alpha Channel.

This week, you are asked to turn in 4 items:

  1. one original color photo (your own)
  2. Black and white photo after “Black & White’ adjustment
  3. Black and white photo after Dodge and Burn
  4. screen capture, shows you have saved the file with alpha

B&W Photos & Darkroom Techniques

Turning Color images into Black & White images

Turning an RGB color image into a “black and white’ image is not straightforward process. There are two reasons for this,

  1. Luminosity: 100% Green appears to be brighter than 100% Red and 100% Blue.  ‘¨100% Blue looks darker than 100% Red and 100% Green.  You can average the three color channels to produce a desaturated gray image, but it doesn’t reproduce the correct luminance of the original color image.RGB Luminance Value = 0.3 Red + 0.59 Green + 0.11 Blue
    Screen Shot 2015-08-31 at 11.04.06 AM
  2. Sometimes, the photographer or artists prefer a darker or lighter shade for a particular color in the photograph.  For example, when you are converting a colored portrait of your friend, you might prefer the skin tone to be brighter to reduce skin discolorations on the skin or darker to make the skin look tanned.

“Black & White’ is a standard Photoshop adjustment you can find in the Top Menu ->Image->Adjustment area. (This is the destructive version.) You can also find it as an Adjustment Layer through the Adjustments interface (This is a non-destructive method).

You can compare the result of “Black & White’ Adjustment Layer to “Desaturate’ Adjustment Layer to see the difference between the method simply averaging the three channels to a more complex conversion.

  • Reducing colors: Image menu -> Adjustments -> Hue/Saturation (also you can use an adjustment layer)
  • Adding a color to BW image: Image menu -> Adjustments -> Hue/Saturation (and turn on “colorize’)
  • Desaturating: Image menu -> Adjustments -> Desaturate

Dodge and Burn

Read about Dodge and Burn tools here at Adobe

This is a good basic tutorial for dodge and burn EXCEPT that he did not create a duplicate background layer first – this is a destructive technique so it’s good to duplicate the first layer and work on a copy rather than the original layer.

Alpha Channels

The color information of pixels is stored in three different channels, Red, Green and Blue. In Adobe Photoshop, you can see the channels in “Channels’ palette. If you can’t find it, use the Top Menu -> Window menu to open.

Read the Basic of Channels (Adobe Photoshop Help, text)

Watch this movie from Adobe on Saving Alpha Channels (will open in a new window):

fancy image link to video from adobe



Further Reference

Advanced tutorial on Dodging and Burning in combination with Curve Adjustments for nondestructive editing from a professional photographer and retoucher, Zoë Noble:


Week 6 Part II - A & B


raven color
Original image
b/w adjustment
Original image with default black and white adjustment layer settings
default b/w settings
There are other preset settings available in the dropdown
raven on snow
After using dodge and burn tools to fix brightness of the mountain and to draw attention to the raven.

Use  a photograph of your choice, but it must be your own*.  

Demonstrate the  Black and White adjustment function and Dodge and Burn tools on the image. Try to enhance the overall image with the Dodge and Burn process.

*The reason why I ask you start from your own image is, the photo on the Internet or stock photo collection often already have some brightness and contrast enhancement. I also want you to think about the enhancement you’d do when you take/look for photos.

Set the image resolution less than 1000 pixels (width or height, whichever greater). Save the image after Black & White adjustment, and then save again as a different name after Dodge and Burn.

Please post on the blog: original color photo, black and white before dodge and burn, and black and white after dodge and burn. Also post a snapshot of your black and white settings on your adjustment layer and take a few notes on what you did.



Step 1: Take a photograph of you or someone else (please obtain their permission).  When you take a photo, place the subject in the middle of the composition. You  can use photos you have taken before, as long as you have the subject in the middle and close-up.

Step 2: Select the area you don’t want to make transparent.

Step 3: Follow the steps shown in the   in the Adobe TV video above, and store the selected area into the Alpha Channel.

Step 4: Make sure you have 4 Channels, Red, Green, Blue and Alpha channel. Your Alpha channel should show the shape of your selection as white shape on black background.

selfie w alpha channel

Step 5: Save your image with TIFF format with no layers but with Alpha channel. You can apply LZW compression.

Step 6: If you view the image in Preview (Macintosh) or the file icon in Windows window, and the background of the image is blank (white or gray), you successfully save the image with Alpha.

Step 7: Capture a your screen showing the alpha channel in Photoshop or a preview of the image with transparent/empty background. (Please show the proof that you understood and created the Alpha channel successfully).

alpha example

Step 7:  Send Jennifer the TIFF file or Photoshop file including the Alpha channel in Google Drive, and also post the screenshot to this blog

Journal & Discussion

Create a new post for all of your images for Week 6 Part II and a brief reflection on your process for A&B. Some questions to think about are:

  • Do Alpha Channels make sense in terms of color selection?
  • How might you use Alpha Channels in the future?
  • What application would exporting the TIFF with Alpha Channels afford?



Do a Google search for other tutorials and videos about Alpha Channels or look for other resources and examples. Post a link to any you found particularly helpful in your journal post this week. It is not an intuitive topic so getting a few different explanations can be helpful for everyone.

Commenting on others’ posts is encouraged.