A light is a wave which doesn’t need a medium to propagate . Other examples of waves are water waves , or air waves which need water and air as a medium to propagate .Water , air and sound waves are known as mechanical waves . A wave has the following properties
it has a crest , which is the largest amplitude that this wave can have
it has a direction of propagation
it has a length , which is the distance between any two identical points on a wave , for example the distance between two crests .
it has a period which is time required for an identical point to repeat itself , so for example the time required for the crest at point A to reach point B .
a wave has a frequency , the frequency is 1 over the period . The period represents the amount it takes for a crest to repeat itself . the frequency is 1 over this this period , so it is the number of crest that passes through a point in one second.
Light is an electro magnetic wave , as such it has an electric field , and a magnetic field .
A magnetic field is for example the field that is generated by a magnet . This field can exert a force on certain materials , and attract them.
An electric field is created by attraction and repulsion of electrical charges . An electric charge is a property of matter that causes object to attract or to repel . An example of an electric field is when a ballon is rubbed on hair , the balloon will be charged negatively , and it will attract the hair .
A charged particle produces an electric field , and exerts a force on other charged particles. Charges that have the same sign attracts , and charges that have opposite signs repels . Positively charged particles accelerate in the same direction of the electrical field , and negatively charged particles accelerate in the inverse direction of the electric field .
A magnetic field is produced by moving charged particle , it exerts a force that is perpendicular to the speed of particles , as such it affects the direction of the particles , and not their speed .
A light wave is formed of charged particles . The particles in a light wave are called photon ,these particles create the wave . A light wave has energy , the energy of light wave is related to its frequency as such it is inversely proportional to its length. The higher the frequency , the shorter the wavelength , the higher the energy that a light wave has . The lower the frequency , the longer the wavelength , and the lower the energy that a light wave has .
The range of frequencies and energies of electro magnetic waves is know as the electromagnetic spectrum .The electro magnetic spectrum is classified in :
radio waves , have a length that is larger than 1* 10^-1 m
radio waves are used for radio , television .
micro waves have a length between and 1*10^-4 m and 1* 10^-1m
they are used for micro wave oven , and for radar .
infrared has a length between 7* 10^-7 m and 1 * 10^-4 m
warm bodies release infra red wave length . Infra red waves have a length that is below the length of a red wave which is a wave that we can see . Heat cameras and night vision cameras , use infra red waves .
visible lights has a length between 4 * 10^-7 m and 7 * 10^-7 m . These are waves that we can see . The longest one is the red wave , it has a wavelength of around 700 nm , and the shorted one is the violet it has a wavelength of around 380 nm .
ultra violet waves has a length between 1*10^-8 m and 4 * 10^-7 m
ultra violet waves are used for example in treatment of cancer.
x-rays has a wave length between 1 * 10^-9 m and 1 * 10^-8 m
x-rays waves can be used to check if a bone is broken
gamma rays has a wave length that is shorter than 1*10^-9 m
gamma rays can cause cancer , and they can be used to treat cancer and kill bacteria .
What is a color
Light is an electro magnetic wave , it has a length . We can classify light based on its wavelength . Visible light has a wavelength between 4 * 10^-7 m and 7 * 10^-7 m . Visible light can be seen by the human eye . The length of the wave specify the color that this wave has . The longest wave length that we can see is the red wave length , and the shortest wave length that we can see is the violet .
When all the visible light waves are seen together , we have the white lite . When light hits an object it is either reflected or absorbed . Our eyes absorb the reflected light waves from the object , and we are able to distinguish the colors of a light wave. The black color is the result of an object absorbing all light , or the absence of light
What is a color space or model?
we need a way to represent a color in the computer , so we have what is called the color space or model , which is the model by which we are representing a color in the computer , and creating colors in analog and digital devices .
In a color space or a color model , we have some basic colors from which all other colors are created ,
For example , if our basic colors are the red green and blue , then this color space is the red green blue color space , and it has the basic colors : red , green and blue . All other colors are created by combining these colors . So if you want the red green blue colors form the basis of a 3d coordinate system , where other colors are created by combining the value of these colors together .
Colors in android (32bits , 64bits , Color class)
colors in android are represented through either an int literal or a long literal or as an instance of the Color class , which creates a color represented as an int literal or a long literal . The Color class also has static methods that allow us to create int and long colors literals , and to convert between the different color space .
The int color literal has 32 bits , and it allow us to create only rgb colors where each components has 8 bits . The long color literal has 64 bits and it allow us to create colors that belong to different color space such as XYZ , RGB. The color long was added as of android O or version 8 , as such it is only available for api level 26 and higher .
Creating a 32 bits int rgb color in android
we can create a color in android by using only 32 bits , in this case the color belong to the RGB color space .
8 bits are used to represent the alpha.
alpha is the transparency of the color
when the value of alpha is at its full , the color is fully opaque
when the value of alpha is at its lowest , the color is transparent
8 bits are used to represent the red color
8 bits are used to represent the green color
8 bits are used to represent the blue color
each color and alpha channel takes 8 bit of storage , as such it takes a byte. A byte can have a value between 0 and 255 in decimal inclusive , or it can have a value between 0x00 and 0xFF in hexadecimal .
creating a 32 bits color using an int literal
we can create a color by using an integer literal which is specified in hex , this can be done in code or in xml . The format of the integer literal is
0xAARRGGBB
0x means that we are using hexadecimal to specify the colors . Two hexadecimal digits for each color and alpha are used
The first byte or two hex digits specify the alpha opacity , when it is 0xFF it is fully opaque , when it is 0x00 it is fully transparent .
The second byte or two hex digits are used to specify the red color
the third byte or two hex digits are used to specify the green color
the last byte or two hex digits are used to specify the blue color
in code
public @ColorInt static final int color = 0x00000000;
when creating color using code , we can declare its type as an int , and we must specify the color using a hexadecimal integer literal . The annotation @ColorInt that is used , is optional , and it is just used to annotate that this int is a color .
In this example , we have created an activity called ColorActivity which has a layout called activity_color.xml .
ColorActivity.java
package com.twiserandom.whatisacolor;
import android.graphics.Color;
import android.os.Build;
import android.support.annotation.ColorInt;
import android.support.annotation.RequiresApi;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ImageView;
public class ColorActivity extends AppCompatActivity {
ImageView srgbIv_RED , srgbIv_RED_HALF_ALPHA;
/*
@ColorInt
just used to annotate that this color
not necessary to use
*/
public @ColorInt static final int RED = 0xFFFF0000;
public @ColorInt static final int RED_HALF_ALPHA = 0x7FFF0000;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_color);
srgbIv_RED = (ImageView) findViewById(R.id.srgbIv_RED);
srgbIv_RED_HALF_ALPHA = (ImageView) findViewById(R.id.srgbIv_RED_HALF_ALPHA);
srgbIv_RED.setBackgroundColor(ColorActivity.RED);
srgbIv_RED_HALF_ALPHA.setBackgroundColor(ColorActivity.RED_HALF_ALPHA);
}
}
The activity_color.xml contains a linear layout which has two image views . In the ColorActivity , we get the references for the views and we we set the background to the colors that we have defined .
in xml
to create a color using xml , we must use the colors.xml file located inside the values folder.
This file contains some predefined colors such as the colorPrimary , colorPrimaryDark , colorAccent .
So in this example we have defined a green color , and a green_half_alfa color . Our activity is called ColorActivity.java , which contains the following code
in the ColorActivity class we get the reference to the image views , and we set their background color to the color that we have defined. We use the ContextCompat.getColor method , passing to it the context of our activity which is the this keyword , and the name of the color by using R.color.colorname .
create a 32 bits int color using the Color class static methods
/*
create a color by specifying the components
alpha , red , green , blue
*/
public static int argb( int alpha, int red, int green, int blue)
public static int argb(float alpha, float red, float green, float blue)
/*
create a color by specifying the components
red , green , blue
the alpha component is by default 255 or 1
*/
public static int rgb( int alpha, int red, int green, int blue)
public static int rgb(float red, float green, float blue)
we can create a 32 bits int color by using the argb method , where we specify the color component as either a float or an int . The int value can be between 0 and 255 or 0x00 , and 0xFF , and the float value can be between 0 and 1 .
The float value of the argb method , is the int value divided by 255 . So when it is 1 it means we have specified a color component which has an int value of 255 , and when it is 0 it is as if we have defined a color which has an int value of 0.
In this example we have the ColorActivity class that has an activity_color.xml file . In the ColorActivity we get the reference for two image views , ad we set the background color using the greenColor and greenColorHalfAlpha variable .The variables have a color int value which was created using the static Color class methods .
package com.twiserandom.whatisacolor;
import android.graphics.Color;
import android.support.annotation.ColorInt;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ImageView;
public class ColorActivity extends AppCompatActivity {
ImageView srgbIv_GREEN , srgbIv_GREEN_HALF_ALPHA;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_color);
srgbIv_GREEN = (ImageView) findViewById(R.id.srgbIv_GREEN);
srgbIv_GREEN_HALF_ALPHA = (ImageView) findViewById(R.id.srgbIv_GREEN_HALF_ALPHA);
//create a green color using the rgb static method
@ColorInt int greenColor = Color.rgb(0,255,0);
//create a green color using the argb static method specifying the alpha to be 127 or half transparent
@ColorInt int greenColorHalfAlpha = Color.argb(127,0,0,0);
/* set the background colors of the image views*/
srgbIv_GREEN.setBackgroundColor(greenColor);
srgbIv_GREEN_HALF_ALPHA.setBackgroundColor(ContextCompat.getColor(this, R.color.green_half_alpha));
}
}
the color space that can be represented by using a 64 bits long literal in android are :
rgb (srgb) : 8 bits per color (24 bits) , 8 bits for the alpha channel . (32 bits)
rgb : 16 bits per color (48 bits), 10 bits for alpha , 6 bits for the color space . (64 bits)
xyz : 16 bits per color (48 bits), 10 bits for alpha , 6 bits for the color space . (64 bits)
xyz labs : 16 bits per color (48 bits) , 10 bits for alpha , 6 bits for the color space .(64 bits)
the most used color space is the rgb color , when it uses only 32 bits it is known as srgb . We can create it either by using 32 bits , or we can create it by using 64 bits , in this case the last 32 bits are set to zero .
other colors can be created using the long color representation , in this case we must specify , the color components , the alfa component , and the other color space.
the first 48 bits are used to specify the colors component.
each 16 bits in the first 48 bits is used to specify the color component that belong to the color space that is specified
the ten next bits are used to specify the alfa component
the last 6 bits are used to specify the color space
since it is a little bit complex to create a 64 bit color by using a long literal , we can use the static methods of the Color class to create a 64 bits color .
create a 64 bits long color using the Color class static methods
there are many methods in the Color class that allows us to create a 64 bits long color. A 64 bits color in android can only be create for api level 26 or higher , so for android O or version 8.
We cannot use a long color by views in android , so we must convert it to a color int before usage .
pack(int)->long
public static long pack(@ColorInt int color)
will create an srgb long color , the last 32 bits will be filled with 0 , and the first 32 bits will be the SRGB color .
/*ColorActivity.java*/
package com.twiserandom.whatisacolor;
import android.graphics.Color;
import android.os.Build;
import android.support.annotation.ColorInt;
import android.support.annotation.ColorLong;
import android.support.annotation.RequiresApi;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ImageView;
public class ColorActivity extends AppCompatActivity {
ImageView ivColor;
@RequiresApi(api = Build.VERSION_CODES.O) /*Long Color can only be used for android version O or higher */
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_color);
/*Get the reference for the color imageViews*/
ivColor = (ImageView) findViewById(R.id.ivColor);
/*create a long color */
@ColorLong Long aLongColor = Color.pack(0xFFFF0000);
/*Convert long color to int*/
/*Long color cannot be used with android view*/
@ColorInt int anIntColor = Color.toArgb(aLongColor);
ivColor.setBackgroundColor(anIntColor);
}
}
/*activity_color.xml*/
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<ImageView
android:id="@+id/ivColor"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1" />
</LinearLayout>
in this example we have an image view . We get the reference to the image view . we create a 64 bit srgb color , and later convert it to a 32 bit rgb color in order for it to be used by the image view as its background color .
pack(float red , float green , float blue )->long
public static long pack(float red, float green, float blue)
will create a 64 bit SRGB color from the red green and blue component.
The red , green and blue components are specified as a float between 0 and 1 .
The created color is srgb
it uses the first 32 bits of the 64 bits long
the last 32 bits are filled with zero.
each color will have an 8 bits
the alfa channel will have bits , which will be 0xFF by default .
/*ColorActivity.java*/
import android.graphics.Color;
import android.os.Build;
import android.support.annotation.ColorInt;
import android.support.annotation.ColorLong;
import android.support.annotation.RequiresApi;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ImageView;
public class ColorActivity extends AppCompatActivity {
ImageView ivColor;
@RequiresApi(api = Build.VERSION_CODES.O) /*Long Color can only be used for android version O or higher */
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_color);
/*Get the reference for the color imageViews*/
ivColor = (ImageView) findViewById(R.id.ivColor);
/*create a long color */
@ColorLong Long aLongColor = Color.pack(0,1,0);
/*Convert long color to int*/
/*Long color cannot be used with android view*/
@ColorInt int anIntColor = Color.toArgb(aLongColor);
ivColor.setBackgroundColor(anIntColor);
}
}
/*activity_color.xml*
/
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<ImageView
android:id="@+id/ivColor"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1" />
</LinearLayout>
so in this example we have an imageView. We set its background color to green . We created the green color by using the pack methods which takes 3 values that represents red , green , blue. The alpha component has a default value of 1f .
An SRGB color uses only the first 32 bits , the last 32 bits of the long are set tozero . We can use the static method toArgb to convert a color from 64 bits to 32 bits .
pack(float red , float green, float blue , float alpha)->long
this method is similar to the pack(red, green , blue) method , but it takes an additional alpha component to create an SRGB color . It is used the same way as the pack(red,green,blue) method , we just have to specify an additional alpha component .
public static long pack(float red, float green, float blue, float alpha)
we can use this method to create a color either using a srgb colorspace , or rgb color space .
in Srgb color space each color takes 8 bits
in rgb each color takes 16 bits .
in the case of srgb
red , green and blue are [0-255]/255
alfa is [0-255]/255
in the case of rgb
red , green and blue are [0-65535]/65535
alfa is [0-1023]/1023
Color space is specified by using ColorSPace static properties
public static long pack(float red, float green, float blue, float alpha, ColorSpace colorSpace)
/*ColorActivity.java*/
public class ColorActivity extends AppCompatActivity {
ImageView ivColor;
@RequiresApi(api = Build.VERSION_CODES.O) /*Long Color can only be used for android version O or higher */
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_color);
/*Get the reference for the color imageViews*/
ivColor = (ImageView) findViewById(R.id.ivColor);
/*get srgb colorspace*/
ColorSpace srgb = ColorSpace.get(ColorSpace.Named.SRGB);
/*create a long color */
@ColorLong Long aLongColor = Color.pack(1,1,0 , 1 , srgb);
/*Convert long color to int*/
/*Long color cannot be used with android view*/
@ColorInt int anIntColor = Color.toArgb(aLongColor);
ivColor.setBackgroundColor(anIntColor);
}
}
/*activity_color.xml*/
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<ImageView
android:id="@+id/ivColor"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1" />
</LinearLayout>
Creating a Color instance
we can represent a color by using the instance of the Color class . To create an instance of the color class , we must use the valueOf method . The valueOf methods will create a Color instance that represents a 64 bit color .
The methods
valueOf(float r, float g, float b)
valueOf(float r, float g, float b, float a)
valueOf(int)
will create an SRGB color represented by the Color instance . so each color component will take 8 bit . The methods
will create an rgb color where each color is represented by 16 bits , the alfa channel is 10 bits , and the color space is 6 bits .
/*ColorActivity.java*/
package com.twiserandom.whatisacolor;
import android.graphics.Color;
import android.graphics.ColorSpace;
import android.os.Build;
import android.support.annotation.ColorInt;
import android.support.annotation.RequiresApi;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ImageView;
public class ColorActivity extends AppCompatActivity {
ImageView ivColor;
@RequiresApi(api = Build.VERSION_CODES.O) /*Long Color can only be used for android version O or higher */
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_color);
/*Get the reference for the color imageViews*/
ivColor = (ImageView) findViewById(R.id.ivColor);
/*get rgb colorspace*/
ColorSpace srgb = ColorSpace.get(ColorSpace.Named.SRGB);
/*create a Color instance */
Color color = Color.valueOf(0, 1, 1, 1, srgb);
/*
get a 32 bit color from a color instance
*/
@ColorInt int anIntColor = color.toArgb();
ivColor.setBackgroundColor(anIntColor);
}
}
/*activity_color.xml*/
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<ImageView
android:id="@+id/ivColor"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1" />
</LinearLayout>
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