CS178 Assignment 8 - Portraits and Light

A studio-lit portrait of Andrew. Photo by Elena Adams.

Motivation

People are certainly one of the most interesting and most challenging subjects to photograph. For this last assignment, you'll be using all of the skills you've learned during the course to take some stunning portraits. You will need to think about lighting, backgrounds, depth of field, composition, and color. You can also (tastefully) touch up each photo in Photoshop. By now these skills should come quite naturally to you, so you can focus your creative effort on capturing something truly unique or special about your portrait subject.

If you find yourself without anyone willing to model for you this week, you can take a self-portrait for any of the requirements. This is an interesting type of photograph in its own right, and adds a degree of difficulty.

Like last week, there are also a set of exam-style questions at the end of this assignment. Although we will not grade these, they will exercise your understanding of photographic lighting and help you to prepare for the final exam. The answers to these questions will be posted on Sunday, June 1 after the assignment is due.

Instructions

This week there are six photographic requirements. Requirements 1 through 5 must be met by taking pictures of human beings. (Sorry, no portraits of pets, stuffed animals, etc. this week!) Requirement 6 can be met using any subject of your choosing.

Requirements

• Requirement 1: Indoor Traditional Portrait
  Take a portrait of someone using a traditional portrait lighting setup as described in lectures (a key light, a fill light, and possibly a background light and accent/rim light). Unless you have some fancy lighting gear of your own, you should take this picture during your regular section meeting where we will set up a full studio lighting kit.
• Requirement 2: Indoor Natural Light Portrait
  Take a portrait of someone indoors using only non-electric sources of light (a fireplace, candles, the sun, etc). You might want to arrange someone near a window. Think about the light in the same way as for the studio lighting, and comment on how you created a fill light, how you created a key light, etc.
• Requirement 3: Outdoor Available Light Portrait
  Take a portrait of someone outdoors under available lighting only. Comment on what serves as the fill light and key light. If you like, you can also make this one a candid shot, in which the subject is not aware you're taking a photo (or at least appears to not be aware).
• Requirement 4: Flash + Ambient
  Take a portrait which uses a combination of your camera's flash and ambient illumination. Again, comment on what serves as the key light and what serves as the fill light. Remember, you need not point the flash right at the subject - with a small hand-held mirror or white card you can bounce any camera's flash elsewhere.
• Requirement 5: Self Portrait
  Take a portrait where you are both the subject and the photographer (i.e. a self portrait). We suggest using a tripod or ledge to stabilize your camera, maybe in conjunction with the camera's self-timer (or a remote shutter). It's okay to use a mirror if it is used artistically, but please avoid holding the camera at arm's length; this isn't MySpace! Your head must be included in the photo. Pay careful attention to lighting and composition.
• Requirement 6: Non-photorealistic Photograph
  This requirement is unrelated to portraiture, but we thought it would be fun now that you are all experts at image editing. Use a single photograph or combination of photographs to create a single, non-photorealistic image in Photoshop. This requirement is wide open to your creative interpretation, but result must look substantially non-realistic in some way. As a hint: you may want to try taking photographs under multiple different lighting conditions (e.g. at different times of day & night, or flash/no flash with unusual processing); or you may try stitching together pictures of your subject from multiple viewpoints. You may find some inspiration in the artwork of cubists, or the photographic works of David Hockney and Jeremy Kidd. An HDR photo meets this requirement only if you use non-realistic, artistic tone mapping.

Upload your photos and add comments.

Example Solution

Please remember that the photographs that you submit for each assignment must be taken by you specifically for this course. Do not reuse old photographs that you may have laying around, even if they perfectly meet one of the requirements!

If you have questions or comments about the photos we used in the example solution, feel free to add them as comments below the corresponding photograph in Picasa Web, or to email us.

Practice problems

• Problem 1a. Betelgeuse is the second brightest star in the constellation Orion (it's Orion's right shoulder). The surface of Betelgeuse has a temperature of about 3500 Kelvin (5840 Farenheit), and for this question you should assume stars are perfect blackbody radiators. If you were to take a photograph of Betelgeuse with your white balance set to daylight (6500 Kelvin), what color would Betelgeuse be in the photo?
  • a) Reddish
  • b) Greenish
  • c) Blueish
  • d) Whitish

• Problem 1b. What color would Betelgeuse appear if you instead set the white balance to tungsten (3200 Kelvin)?
  • a) Very red
  • b) Slightly red
  • c) Slightly blue
  • d) Very blue

• Problem 2a. As every scout knows, you can start a fire on a sunny day by focusing the sun's image on a piece of paper placed on the ground. ---------(Warning: If you rush out to test this, be careful! Never look at the sun directly, never hold a magnifying glass between your eye and the sun, and never look directly at its focused spot on a white surface. Sunglasses are not enough to protect you from doing any of these things. Glacier goggles or welder's helmets are sufficient for brief glances at the white surface, but not at the sun.) Is the luminance of the sun as seen from the focal point of the lens (where the light rays converge, at the piece of paper) more, less, or the same as the luminance as seen from same point in the absence of the magnifying glass? Select the correct choice:
  • a) more than
  • b) less than
  • c) the same

• Problem 2b. Is the luminous intensity at the focal point more, less, or the same as the luminous intensity at the same point in the absence of the magnifying glass? Select the correct choice.
  • a) more than
  • b) less than
  • c) the same

• Problem 2c. Is the total luminous power (in lumens) reaching the entire piece of paper more, less, or the same as the power reaching the paper in the absence of the magnifying glass? Select the correct choice. Assume the piece of paper is much larger than the magnifying glass.
  • a) more than
  • b) less than
  • c) the same

• Problem 3. True or False: You can think of a diffuse (or Lambertian) surface as being made of a bunch of tiny reflectors, all basically lying flat across the surface of the object.

• Problem 4. True or False: To verify the claim that, on a sunny day with a blue sky, shadowed areas should be about 1/5 as bright as non-shadowed areas, you can take a JPEG image and measure the ratio of pixel values in those two areas.

• Problem 5. Simple demosaicing algorithms based on linear interpolation are likely to fail on which of the following scene subjects? Circle all that apply.
  • (a) A bright orangewall
  • (b) A picket fence 50 feet away
  • (c) A fabric with thin stripes on it
  • (d) A transclucent green vase
  • (e) None of the above scenes will cause problems.

• Problem 6. If a spotlight has a uniform radiant intensity of 10 W/sr over its whole cone of light, and the cone subtends 2 steradians, how much total power will fall on a large white wall 10 meters away when the spotlight is pointed at it? Assume the wall is larger than the lit area created by the spotlight. Circle the best answer.
  • a) 5W
  • b) 10W
  • c) 20W
  • d) 40W

  Since the wall is larger than the lit area created by the spotlight, all of the power created by the light will fall on the wall. With a radiant intensity of 10 W/sr over 2 sr, the total light power output of the spotlight is 10 W/sr * 2 sr = 20 W.

• Problem 7. If you want to bring out the most detail in a rough surface, you should light it with (circle the best answer):
  • a) grazing light
  • b) direct light
  • c) spotlight
  • d) diffuse light

Peer Grading

You should follow the same rubric as the previous assignments.

Due Date

Assignments are generally due on Sunday at midnight at the end of the week in which they're assigned. This leaves you free to start thinking about the next assignment during your next section. Sometimes lateness is unavoidable. In such circumstances, be sure to read the lateness policy from the course outline, or contact your TA.