CS178 Assignment 8 - Portraits and Light

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

Motivation

People are possibly the single most interesting subject to photograph. So for this last assignment, you'll be taking all the skills you've learned during the course and taking some portraits. You should think about lighting, backgrounds, depth of field, composition, and color, and you should (tastefully) touch up each photo in Photoshop. By now, many of these skills will come quite naturally to you.

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

Similarly to last week, there are also a set of exam-style questions to exercise your understanding of light. This might seem like a lot of work, but we've given you more time than we usually do. This assignment is due Wednesday June 3 at midnight.

Instructions

This week there are five photographic requirements, which are similar to previous weeks, and then some questions on light for you to work through.

Requirements

Requirement 1: Indoor Traditional Portrait
Take a portrait of someone using a traditional portait 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 section.
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: Non-photorealistic Combination
This requirement is unrelated to portraiture, but we thought it would be fun to do while you're learning about image editing in lectures. Use a combination of photographs to create a single non-photorealistic image in Photoshop. You must use multiple photographs of different subjects (or the same subject from multiple points of view) as source images, and the result must look nonrealistic.

Upload your photos and add comments.

Upload your photos using the Picasa account you created in the first week to a public Picasa album titled "CS178 Assignment 8 - Portraiture". Add comments below each photo explaining what relevant camera settings you used and why, how you set up the lighting, any image processing done to the photograph afterwards, and most importantly, which requirement the photo covers.

Example Solution

We've put up an example solution to the photographic requirements in this assignment to both let you know what we expect, and hopefully also inspire you to take better photos than the TAs can. You don't have to meet the assignment requirements in the same way as we did - surprise us!

One caveat: In our example solutions we may reuse photos we already had lying around, or borrow photos from other people to illustrate a point. Don't do this - your work for each assignment should be done by you specifically for the course.

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.

Grading

As usual, we will assign grades based on whether you met the requirements of the assignment. For each requirement, you'll be given a check for meeting the requirement, check-minus for not quite meeting the requirement, or check-plus if you do something spectacular that makes your grader's jaw drop.

Due Date

11:59PM, Wednesday, June 2, 2009

We will accept no late assignments or replacement photos after midnight on Sunday June 6. Here's the lateness policy from the course outline:

Since the assignments come in rapid succession, it is important that each be completed on time. Replacing photos after the deadline is not allowed, and will be treated as a violation of the honor code. To allow for unforeseeable circumstances, you will be allowed up to two weekdays of grace for up to two of your assignments. Beyond this, late assignments will be penalized by 10% of the grade for that assignment per weekday that they are late. Exceptions to this late policy will be made only in the case of a necessary (non-pleasure) trip approved in advance by the TA for your section, or severe illness. If you do not submit one of the assignments at all, you will fail the course, even if you are taking it pass/fail. In this case, or if you believe you are in danger of failing, it is your responsibility to come talk to us before the end of the course. Incompletes are given only in exceptional circumstances.

Practice technical questions

These questions are for your own educational benefit; you do not need to submit your answers. After the assignment is due we will select the correct answers in bold.

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?

Reddish

Greenish
Blueish
Whiteish

1b) What color would Betelgeuse appear if you instead set the white balance to tungsten (3200 Kelvin)?

Very red
Slightly red
Slightly blue

Very blue

2a) Match the materials listed below with the gonionmetric diagrams at http://graphics.stanford.edu/~abadams/goniometric.png. Firstly, glossy black plastic:

Diagram A
Diagram B
Diagram C

Diagram D

2b) Glossy white plastic

Diagram A
Diagram B
Diagram C
Diagram D

2c) White matte paper

Diagram A
Diagram B

Diagram C
Diagram D

2d) Black matte paper

Diagram A

Diagram B
Diagram C
Diagram D

3) Last night I took a digital photograph of the moon. This morning the Stanford Daily reported that the moon had left its orbit and was on a collision course with Earth. By tonight it will be half the distance from the earth that it was last night. How should I adjust my camera so that the moon's surface will be the same value in each pixel of tonight's photograph as it was last night? Circle the best answer. Assume the moon is homogeneously colored across its visible surface.

(a) Double the exposure time
(b) Halve the exposure time
(c) Leave the exposure time alone

(d) Multiply the exposure time by sqrt(2)
(e) There is a correct adjustment, but none of the above answers is correct
(f) There is no adjustment that will work; you cannot match the pixel values

4a) 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 radiance 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 radiance as seen from same point in the absence of the magnifying glass? Select the correct choice:

more than
less than
the same

4b) Is the irradiance at the focal point more, less, or the same as the irradiance at the same point in the absence of the magnifying glass? Select the correct choice.

more than

less than
the same

4c) Is the total radiant power (in watts) 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.

more than
less than
the same

5) Total luminance can be expressed as the sum of the human tristimulus responses ρ, β, γ.

True

False

6) 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.

True
False

7) 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.

True
False