Color¶

Class Color is a subclass of EV3. You can use it to read values from a single color sensor without any knowledge of direct command syntax. The color sensor measures light intensity or colors. This may be reflected light. If you like to use multiple color sensors simultaneously, then create more than one instance of this class.

The reflected intensity of red light¶

Class Color has an attribute reflected, which is of type int and tells the intensity of the reflected red light in percent. This says: it switches on red light and then measures the reflection from a surface. From then on the red light shines permanently. With constant surface type and color, this allows to measure small distances (this needs calibration). Alternatively, when the distance is constant, it allows to distinguish dark from bright surfaces (e.g. for line followers). Because of the red light, it tends to categorize red surfaces as bright and green surfaces as dark.

Take an USB cable and connect your EV3 device with your computer. Replace MAC-address 00:16:53:42:2B:99 by the one of your EV3 brick, connect a color sensor (it may be of type ev3.NXT_COLOR or ev3.EV3_COLOR) with PORT 1, then start this program:

import ev3_dc as ev3

my_color = ev3.Color(
        ev3.PORT_1,
        protocol=ev3.USB,
        host='00:16:53:42:2B:99'
)

print(f'reflected intensity is {my_color.reflected} %')

Some remarks:

You already know, how to change the program for using protocols Bluetooth or WiFi.

Run the program multiple times with different surface colors and distances.

Test what happens, when no sensor is connected to PORT 1.

Test what happens, when another sensor type is connected to PORT 1.

Every reference of property reflected starts a new communication between the program and the EV3 device.

Switch on verbosity by setting attribute verbosity to value 1 and you will see the communication data.

My program’s output was:

reflected intensity is 17 %

Recognize colors¶

Class Color has an attribute color, which is of type int and tells the color of the surface in front of the sensor. This ist done when the sensor shines white.

Take an USB cable and connect your EV3 device with your computer. Replace MAC-address 00:16:53:42:2B:99 by the one of your EV3 brick, connect a color sensor (it may be of type ev3.NXT_COLOR or ev3.EV3_COLOR) with PORT 1, then start this program:

import ev3_dc as ev3

my_color = ev3.Color(
        ev3.PORT_1,
        protocol=ev3.USB,
        host='00:16:53:42:2B:99'
)

color = (
    'none',
    'black',
    'blue',
    'green',
    'yellow',
    'red',
    'white',
    'brown'
)[my_color.color]
print('the color is', color)

Some remarks:

You already know, how to change the program for using protocols Bluetooth or WiFi.

Run the program multiple times with different surface colors in front of the sensor.

Test what happens, when no sensor is connected to PORT 1.

Test what happens, when another sensor type is connected to PORT 1.

Every reference of property color starts a new communication between the program and the EV3 device.

Switch on verbosity by setting attribute verbosity to value 1 and you will see the communication data.

The light emission is permanent. Therefore the sensor permanently switches on white light.

NXT-Color does never answer with 0 or 7, it therefore will never see none or brown.

You can use the constants ev3.NONECOLOR, ev3.BLACKCOLOR, etc. if your program asks for specific colors.

My program’s output was:

the color is green

Red green blue Color Intensities¶

Class Color has an attribute rgb_raw, which is a tuple of three int type values and tells the color of the surface in front of the sensor. This ist done when the sensor shines with all three led colors on.

Take an USB cable and connect your EV3 device with your computer, connect a color sensor (it must be of type ev3.EV3_COLOR) with PORT 1, then start this program:

import ev3_dc as ev3

my_color = ev3.Color(
        ev3.PORT_1,
        protocol=ev3.USB
)
print(my_color.rgb_raw)

Some remarks:

You already know, how to change the program for using protocols Bluetooth or WiFi.

Run the program multiple times with different surface colors in front of the sensor. Also vary the distance from the surface.

Be aware, that every reference of property rgb_raw starts a new communication between the program and the EV3 device.

Switch on verbosity by setting attribute verbosity to value 1 and you will see the communication data.

The light emission is permanent. Therefore the sensor permanently switches on all its LED light colors.

My program’s output with a white surface in front of the sensor:

RawRGBColor(red=253, green=292, blue=183)

Some remarks:

Maybe you did not expect to get values higher than 255. Keep in mind, that sensor ev3.EV3_COLOR is normed to values from 0 to 1024.

The measurement is done with reflected light and consequently depends on the color spectrum of the light source. The blue part of the light source’s frequencies is under-represented, the green part is over-represented and this is what you find in the result above.

The result from the white surface can be used for a color balance, which is well known from photography or image processing.

Geometry also plays its role in the measured intensities. The blue light source is closest to the sensor, the green one is most distant. As a consequence, smaller distances between sensor and surface result in more balanced results.

Balanced red green blue Color Intensities¶

Class Color has an attribute rgb, which is very similar to attribute rgb_raw, but is white balanced.

Take an USB cable and connect your EV3 device with your computer, connect a color sensor (it must be of type ev3.EV3_COLOR) with PORT 1, then start this program:

import ev3_dc as ev3

my_color = ev3.Color(ev3.PORT_1, protocol=ev3.USB)
my_color.rgb_white_balance = (253, 292, 183)
print(my_color.rgb)

Some remarks:

This program uses the raw values, measured on a white surface to do the white balance.

Replace the values for the white balance by the result of your own measurement.

Run the program multiple times with different surface colors in front of the sensor. Also vary the distance from the surface.

My program’s output with a green surface in front of the sensor:

RGBColor(red=43, green=114, blue=54)

Some remarks:

Attribute rgb is normed to values between 0 and 255. This is what you know as rgb colors.

Use a color picker, like this one to control your results.

Ambient light intensity¶

Class Color has an attribute ambient, which is of type int and tells the intensity of the ambient light in percent. One would expect, that this ist done without any light emission. Surprisingly the EV3_Color sensor switches on its blue light, when it measures ambient light. The NXT-Color sensor behaves as expected, it switches its light off.

Take an USB cable and connect your EV3 device with your computer. Replace MAC-address 00:16:53:42:2B:99 by the one of your EV3 brick, connect a color sensor (it may be of type ev3.NXT_COLOR or ev3.EV3_COLOR) with PORT 1, then start this program:

import ev3_dc as ev3

my_color = ev3.Color(
        ev3.PORT_1,
        protocol=ev3.USB,
        host='00:16:53:42:2B:99'
)

print(f'ambient intensity is {my_color.ambient} %')

Some remarks:

You already know, how to change the program for using protocols Bluetooth or WiFi.

Run the program multiple times with different light intensity in front of the sensor.

Test what happens, when no sensor is connected to PORT 1.

Test what happens, when another sensor type is connected to PORT 1.

Every reference of property ambient starts a new communication between the program and the EV3 device.

Switch on verbosity by setting attribute verbosity to value 1 and you will see the communication data.

The light emission is permanent. Therefore EV3-Color permanently changes to blue light, NXT-Color permanently switches its light off.

My program’s output was:

ambient intensity is 9 %