Abstract

Objective

In this experiment you will investigate how different color profiles combine colors to produce an image.

Introduction

When thinking about digital photography, it is important to know what you will use your photo for. You want your photo to look good whether it is online or in print. Why should this make a difference?

There is a fundamental difference between how color is produced on a screen and by a printer. A screen lights up from behind, and shines the color out of the screen towards your eyes. A printer lays a pigment down on a sheet of paper (usually white) that will block some light from reflecting back to your eye. One process is additive (screen) and one is subtractive (paper).

Each color profile uses separate color channels that are combined to produce the final full color image. How does this work? In this experiment you will investigate two different color profiles, RGB Color and CMYK Color. Which color profile looks best on screen? Which one prints the best photos? You will dissect a full color image and learn to separate the individual color channels. What do the individual color channels look like?

Terms, Concepts, and Questions to Start Background Research

To do this type of experiment you should know what the following terms mean. Have an adult help you search the internet, or take you to your local library to find out more!

• Color Profile
• RGB color (Red, Green, Blue)
• CMYK color (Cyan, Magenta, Yellow, Black)
• Color Channels
• Color Mixing

• How do the separate color channels mix together to form an image?
• What do the individual color channels of an RGB color image look like?
• What do the individual color channels of a CMYK color image look like?

Bibliography

• Digital Expert, 2005. "Color Space Fundamentals," The Sheridan Group. [accessed: 4/24/06]
  http://dx.sheridan.com/advisor/cmyk_color.html
• 2005. "Adobe Digital Kids Club." Adobe Systems, Inc. San Jose, CA. [accessed: 4/24/06]
  http://www.adobe.com/education/digkids/main.html
• Wilson, Tracy V., Nice, K., and Gurevich, G. 2005. "How Digital Cameras Work." HowStuffWorks, Inc. Atlanta, GA. [accessed: 4/24/06]
  http://www.howstuffworks.com/digital-camera.htm

Materials and Equipment

• computer
• Adobe Photoshop
• your favorite photo
• color printer
• photo quality printing paper

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Experimental Procedure

1. On your desktop, create a new folder called "My Photo Experiment" and place a copy of your favorite photo in the folder.
2. Open the photo in Adobe Photoshop.
3. To view the color profile for the image, click "Image" and then "Mode" from the file menu.
4. You will see a list of color profiles with a check next to "RGB" or "CMYK" indicating the current color profile.
5. To begin this experiment, we will start by using RGB color, because it only has three color channels. If the current profile is not RGB then click on "RGB" to select and change the color profile to RGB color.
6. Click on "File" and "Save As" to save this picture as a new file in the folder on your desktop named "My Photo Experiment", naming the file with the letters "RGB" at the end (like "puppyRGB"). Keep all of the settings and file extensions the same.

7. Print the picture on photo quality paper. This is your composite image, and includes all of the color channels.
8. Next, you are ready to view each individual color channel separately.
9. Click "Image" then "Adjustments" and then "Curves" from the file menu.

10. You will see a dialog box that has a square with a diagonal line running across it. Play around by clicking, moving and stretching the line to see what it does to change the image. When you are done experimenting click on "Cancel" and re-open the dialog box.

11. In RGB color, you will have three color channels. To isolate one color channel (Red), you will turn down the other two color channels (Green and Blue).
12. To see the Red channel:
    1. Click "Green" from the drop down menu, click on the top right hand corner of the line and drag it to the bottom right corner.
    2. Then click "Blue" from the drop down menu, click on the top right hand corner of the line and drag it to the bottom right corner.
13. Click "OK" and the dialog box will close. Your picture should look strange. This is your Red channel image, and does not have any of the Green or Blue color information in it.
14. Click on "File" and "Save As" to save this picture as a new file in the folder on your desktop named "My Photo Experiment", naming the file with the letters "Red" at the end (like "puppyRed"). Keep all of the settings and file extensions the same.
15. Print the picture on photo quality paper.
16. Close this image and re-open the RGB image from the desktop folder (puppyRGB).
17. Repeat steps 9-16 for each remaining color channel.
18. To see the Green channel:
    1. Click "Red" from the drop down menu, click on the top right hand corner of the line and drag it to the bottom right corner.
    2. Then click "Blue" from the drop down menu, click on the top right hand corner of the line and drag it to the bottom right corner.
19. To see the Blue channel:
    1. Click "Red" from the drop down menu, click on the top right hand corner of the line and drag it to the bottom right corner.
    2. Then click "Green" from the drop down menu, click on the top right hand corner of the line and drag it to the bottom right corner.
20. Arrange your four photos in a row and compare. How do the individual color channels resemble the composite image? How are they different? Does each color channel look the way you expected it to? How do you think they form the composite image when put together?
21. To compare how a color image is made in CMYK using four color channels (Cyan, Magenta, Yellow and Black), change the color profile to "CMYK" and repeat the experiment.
22. How do the two methods compare? Do any of the individual color channels in RGB look like one of the CMYK channels? Do the composite images look the same or different?

Variations

• Another interesting component of a digital image is the saturation and contrast of the image. To investigate these topics see the Science Buddies project ideas Color Saturation and Digital Photo Contrast for more ideas.
• You can investigate the physics of color mixing using paints or a color wheel. How to some colors mix to form other colors? Which colors are pure colors? Which colors are mixtures of other colors?
• You can also investigate the physics of light waves and color by using prisms. How do prisms separate the colors of light? Can you use containers of water as a color prism? What wavelengths of light correspond to the different colors of the visible spectrum?

• For more science project ideas in this area of science, see Photography, Digital Photography & Video Project Ideas.

Credits

Sara Agee, Ph.D., Science Buddies

Last edit date: 2006-05-31 23:00:00