Quiz 7: Color Conversion

[This quiz is due at the start of class on Monday 10/30]

In class we discussed a variety of color encodings---some very common ones are RGB, CMYK, and HSV. In this quiz you'll get a chance to play around with these encodings. Recall that in particular...

• RGB encodes a color as a red, green, blue triple. RGB is an additive color model. Here you can assume that each of the three channels is given by a value between 0 and 1. (Another common encoding uses values between 0 and 255, inclusive, since these values are often encoded as a single 8-bit byte.) Note that order matters! Red comes first, then green, then blue.

• CMYK encodes a color as cyan, yellow, magenta, and black. CMYK is a subtractive color model. Again you should assume each channel is encoded by a value between 0 and 1, in CMYK order.

• HSV encodes a color as hue, saturation, and value. Here you can assume that the hue is a value between 0 and 360, and both saturation and value are between 0 and 1.

### Part 1: Name That Color!

For each of the named colors below, give an expression for that color in the specified color encoding. There are of course many possible answers, since the name of a color doesn't precisely pin it down. But you should give something in the right ballpark. Note: using a digital color picker is considered cheating! :-)

• A. bright orange (CMYK)
• B. dark green (HSV)
• C. brown (RGB)
• D. white (CMYK)
• E. dark gray (HSV)
• F. bright yellow (RGB) --- write this one as a hexidecimal string, rather than a triple of 0-1 values

### Part 2: Color interpolation

Suppose you want to interpolate between medium green and bright magenta. Values for these two colors are given in each of the three color spaces. For each of the three color spaces, linearly interpolate these values, using 50% of medium green and 50% of bright magenta.

• A. What color do you get in each of the three cases (i.e., give an English name like "blue" or "green")?
• B. Why do you get three different results?
(medium green)
RGB    CMYK    HSV
0      100     149
166    0       1.0
81     100     0.65
0

(bright magenta)
RGB    CMYK    HSV
236    0       324
0      100     1.0
140    0       0.93
0