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Why oval shape is sinuous and pixelated? [duplicate]

I have tried using the method drawOval with equal height and width but as the diameter increases the circle becomes worse looking. What can I do to have a decent looking circle no matter the size. How would I implement anti-aliasing in java or some other method.

As it turns out, Java2D (which I'm assuming is what you're using) is already pretty good at this! There's a decent tutorial here: http://www.javaworld.com/javaworld/jw-08-1998/jw-08-media.html
The important line is:
graphics.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);

you can set rendering hints:
Graphics2D g2 = (Graphics2D) g;
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);

Two things that may help:
Use Graphics2D.draw(Shape) with an instance of java.awt.geom.Ellipse2D instead of Graphics.drawOval
If the result is still not satisfactory, try using Graphics2D.setRenderingHint to enable antialiasing
Example
public void paint(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
Shape theCircle = new Ellipse2D.Double(centerX - radius, centerY - radius, 2.0 * radius, 2.0 * radius);
g2d.draw(theCircle);
}
See Josef's answer for an example of setRenderingHint

Of course you set your radius to what ever you need:
#Override
public void paint(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g2d.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
Ellipse2D.Double hole = new Ellipse2D.Double();
hole.width = 28;
hole.height = 28;
hole.x = 14;
hole.y = 14;
g2d.draw(hole);
}

Thanks to Oleg Estekhin for pointing out the bug report, because it explains how to do it.
Here are some small circles before and after. Magnified a few times to see the pixel grid.
Going down a row, they're moving slightly by subpixel amounts.
The first column is without rendering hints. The second is with antialias only. The third is with antialias and pure mode.
Note how with antialias hints only, the first three circles are the same, and the last two are also the same. There seems to be some discrete transition happening. Probably rounding at some point.
Here's the code. It's in Jython for readability, but it drives the Java runtime library underneath and can be losslessly ported to equivalent Java source, with exactly the same effect.
from java.lang import *
from java.io import *
from java.awt import *
from java.awt.geom import *
from java.awt.image import *
from javax.imageio import *
bim = BufferedImage(30, 42, BufferedImage.TYPE_INT_ARGB)
g = bim.createGraphics()
g.fillRect(0, 0, 100, 100)
g.setColor(Color.BLACK)
for i in range(5):
g.draw(Ellipse2D.Double(2+0.2*i, 2+8.2*i, 5, 5))
g.setRenderingHint( RenderingHints. KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON)
for i in range(5):
g.draw(Ellipse2D.Double(12+0.2*i, 2+8.2*i, 5, 5))
g.setRenderingHint( RenderingHints. KEY_STROKE_CONTROL,
RenderingHints.VALUE_STROKE_PURE)
for i in range(5):
g.draw(Ellipse2D.Double(22+0.2*i, 2+8.2*i, 5, 5))
#You'll probably want this too later on:
#g.setRenderingHint( RenderingHints. KEY_INTERPOLATION,
# RenderingHints.VALUE_INTERPOLATION_BICUBIC)
#g.setRenderingHint( RenderingHints. KEY_RENDERING,
# RenderingHints.VALUE_RENDER_QUALITY)
ImageIO.write(bim, "PNG", File("test.png"))
Summary: you need both VALUE_ANTIALIAS_ON and VALUE_STROKE_PURE to get proper looking circles drawn with subpixel accuracy.

Inability to draw a "decent looking circle" is related to the very old bug 6431487.
Turning antialiasing on does not help a lot - just check the kind of "circle" produced by the drawOval() or drawShape(Eclipse) when the required circle size is 16 pixels (still pretty common for icon size) and antialiasing is on. Bigger antialiased circles will look better but they are still asymmetric, if somebody will care to look at them closely.
It seems that to draw a "decent looking circle" one has to manually draw one. Without antialiasing it will be midpoint circle algorithm (this question has an answer with a pretty java code for it).

EDITED: 06 September 2017
That's an algorithm invented by me to draw a circle over a integer matrix. The same idea could be used to write a circle inside a BufferedImage.
If you are trying to draw that circle using the class Graphics this is not the answare you are looking for (unless you wish to modify each color-assignement with g.drawLine(x, y, x+1, y), but it could be very slow).
protected boolean runOnCircumference(int[][] matrix, int x, int y, int ray, int color) {
boolean ret;
int[] rowUpper = null, rowInferior = null, rowCenterUpper = null, rowCenterInferior = null;
if (ret = ray > 0) {
if (ray == 1) {
matrix[y][x + 1] = color;
rowUpper = matrix[++y];
rowUpper[x] = color;
rowUpper[x + 2] = color;
matrix[y][x] = color;
} else {
double rRay = ray + 0.5;
int r = 0, c = 0, ray2 = ray << 1, ray_1 = ray - 1, halfRay = (ray >> 1) + ray % 2, rInf,
ray1 = ray + 1, horizontalSymmetricOldC;
// draw cardinal points
rowUpper = matrix[ray + y];
rowUpper[x] = color;
rowUpper[x + ray2] = color;
matrix[y][x + ray] = color;
matrix[ray2 + y][x + ray] = color;
horizontalSymmetricOldC = ray1;
rInf = ray2;
c = ray_1;
for (r = 0; r < halfRay; r++, rInf--) {
rowUpper = matrix[r + y];
rowInferior = matrix[rInf + y];
while (c > 0 && (Math.hypot(ray - c, (ray - r)) < rRay)) {
rowUpper[x + c] = color;
rowUpper[x + horizontalSymmetricOldC] = color;
rowInferior[x + c] = color;
rowInferior[x + horizontalSymmetricOldC] = color;
// get the row pointer to optimize
rowCenterUpper = matrix[c + y];
rowCenterInferior = matrix[horizontalSymmetricOldC + y];
// draw
rowCenterUpper[x + r] = color;
rowCenterUpper[x + rInf] = color;
rowCenterInferior[x + r] = color;
rowCenterInferior[x + rInf] = color;
horizontalSymmetricOldC++;
c--;
}
} // end r circle
}
}
return ret;
}
I tried it so many times, verifying manually it correctness, so I think it will work. I haven't made any range-check just to simplify the code.
I hope it will help you and everyone wish to draw a circle over a matrix (for example, those programmer who tries to create their own videogames on pure code and need to manage a matrix-oriented game-map to store the objects lying on the game-map [if you need help on this, email me]).

Java Swing GUI for equation 5((θ/β) - cos(2πθ/β)) - to draw continuous graph

This is an extension to my previous question posted here -- Java Swing GUI for equation 5((θ/β) - cos(2πθ/β))
I have implemented the Java program based on the answers provided in the post an here is my program:
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class DisplacementFunctionNew extends JFrame {
public DisplacementFunctionNew() {
setLayout(new BorderLayout());
add(new CosGraph(), BorderLayout.CENTER);
}
public static void main(String[] args) {
DisplacementFunctionNew frame = new DisplacementFunctionNew();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(6000, 6000);
frame.setVisible(true);
frame.setLocationRelativeTo(null);
frame.setTitle("SineWave");
}
class CosGraph extends JPanel {
public void paintComponent(Graphics g) {
int graphHeight = 5; // Declared this to set the height of graph based on the value given here.
super.paintComponent(g);
int xBase = 100;
int top = 100;
int yScale = 100;
int xAxis = 360;
int yBase = top + yScale;
g.drawLine(xBase, top, xBase, top + 2 * yScale);
g.drawLine(xBase, yBase, xBase + xAxis, yBase);
g.setColor(Color.red);
double maxY = 0;
for (int i = 0; i < 360; i++) {
maxY = Math.max(maxY, Math.abs(getValue(i)));
}
int x, y;
for (int i = 0; i < 360; i++) {
x = xBase + i;
y = yBase - (int) (getValue(i)*graphHeight / maxY * yScale);
g.drawLine(x, y, x, y);
}
}
private double getValue(int theta) {
int beta = 45;
double b = (theta / (double) beta);
double angle = 2 * Math.PI * (b);
double c = Math.cos(angle);
double s = (b - c);
return s;
}
}
}
Now in this program I want to have a variable called graphHeight that helps to increase the height of the graph. If I give the value of the variable as 1 then I can see the output like this:
Now if I try to increase the height to 5 then I get the graph but it is not shown smoothly or continuous curve, I get the output like this:
Can someone please help me how to get the output as smooth continuous curve?

You are drawing a curve using points. You are placing one point at each location on the x axis -- this makes sense to do.
When the graph is small, it looks fine, because the y separation of these points is relatively small. However, as you increase the graph size, this flaw becomes more noticeable.
The solution here is to fill in the vertical space with lines. You have a few options for the exact implementation of this:
Draw a line from [x(i), y(i)] to [x(i+1),y(i+1)] -- this is easy, but may not look the way you want.
Draw a line from [x(i), y(i)] to [x(i),y(i+1)] -- this is still pretty easy, but it won't be quite correct: you're continuing up so that you could be an entire pixel off.
Draw a line from [x(i), y(i)] to [x(i),(y(i)+y(i+1))/2], and then from [x(i+1), (y(i)+y(i+1))/2] to [x(i+1),y(i+1)] -- this is what 1 should do (neglecting anti-aliasing), and will be the most correct of your possible options.
I would suggest number 3. Note that you can implement this with a loop of the form:
int lastY = yBase - (int) (getValue(0)*graphHeight / maxY * yScale);
for (int i = 1; i < 360; i++) {
x = xBase + i;
y = yBase - (int) (getValue(i)*graphHeight / maxY * yScale);
g.drawLine(x-1, lastY, x-1, (y+lastY)/2);
g.drawLine(x, (y+lastY)/2, x, y);
}
If the one pixel overlap bothers you, you can make it a bit more complex such that the second line starts at +/- 1 pixel (depending on if the function is increasing or decreasing).
Alternatively, you can implement number 3 by manually drawing the line, using a for loop, and basically write a special-case version of Bresenham's line algorithm.

You use graphHeight to define the y of the next point to be painted with g.drawLine(x, y, x, y);. The distance between drawn points will be related to the graphHeight variable

Java: BufferedImage INT_RGB Alpha?

Is there any way to use alpha in a BufferedImage that uses INT_RGB? I'm using a 1D pixel array to render sprites onto the screen but I wanted to be able to use Alpha. Is there any way to mix the colors and achieve some sort of layer system like in photoshop?
I've been trying to create some custom alpha by mixing colors, but im not quite sure how to do that either.
This is what I have so far:
BufferedImage & Pixel array:
BufferedImage image = new BufferedImage(width / scale, height / scale, BufferedImage.TYPE_INT_RGB);
int[] pixels = ((DataBufferInt)image.getRaster().getDataBuffer()).getData();
Method used to render sprite:
public static void drawSprite(Sprite sprite, int coord_x, int coord_y) {
int boundsX = (coord_x + sprite.width),
boundsY = (coord_y + sprite.height),
index = -1, pixels[] = Screen.pixels;
for(int y = coord_y; y < boundsY; y++) {
for(int x = coord_x; x < boundsX; x++) {
index++;
if(Screen.pixels[x + y * width] == 0) {
Screen.pixels[x + y * width] = sprite.pixels[index];
} else {
int[] screenPixel = intToARGB(Screen.pixels[x + y * width]);
int[] spritePixel = intToARGB(sprite.pixels[index]);
int[] newPixel = new int[4];
newPixel[0] = (screenPixel[0] + spritePixel[0]) / 2;
newPixel[1] = (screenPixel[1] + spritePixel[1]) / 2;
newPixel[2] = (screenPixel[2] + spritePixel[2]) / 2;
newPixel[3] = (screenPixel[3] + spritePixel[3]) / 2;
Screen.pixels[x + y * width] = Integer.parseInt((Integer.toString(newPixel[0]) +
Integer.toString(newPixel[1]) +
Integer.toString(newPixel[2]) +
Integer.toString(newPixel[3])));
}
}
}
}

Is there any way to use alpha in a BufferedImage that uses INT_RGB?
Short answer: No.
Long answer: No, a BufferedImage of type INT_RGB doesn't contain alpha (unless you redefine what R, G and B means, that is...). But it's of course possible to correctly compose other types of BufferedImage with alpha (like TYPE_INT_ARGB, TYPE_4BYTE_ABGR or even TYPE_BYTE_INDEXED with alpha or transparent pixel in the IndexColorModel) onto a BufferedImage that uses TYPE_INT_RGB. Maybe this is what you are trying to do?
Side note: Java2D already implements image compositing and different types of (Porter/Duff) alpha blending rules in the class AlhpaComposite. Using this class, you get possibly hardware accelerated alpha blending that is super fast. I don't understand why you want to re-implement this.

How can I use the HSL colorspace in Java?

I've had a look at the ColorSpace class, and found the constant TYPE_HLS (which presumably is just HSL in a different order).
Can I use this constant to create a Color from hue, saturation, and luminosity?
If not, are there any Java classes for this, or do I need to write my own?

Most of the given answers here seem to assume that HSL == HSB, which is false. The HSB colorspace is useful (and used) in many cases, but there is one notable exception: CSS. The non-RGB css color functions, hsl() and hsla() are HSL, not HSB. As such, it is very useful to be able to convert to and from HSL in java.
There is a good writeup about the problem here: http://tips4java.wordpress.com/2009/07/05/hsl-color/ TL;DR: the code is here: http://www.camick.com/java/source/HSLColor.java
I have created a gist backup, should the blog ever go down: https://gist.github.com/Yona-Appletree/0c4b58763f070ae8cdff7db583c82563
The methods therein are pretty easy to extract if you don't want to use the whole class.
License
The code appears to be in the public domain, as noted on the "About" page of the blog (https://tips4java.wordpress.com/about/):
We assume no responsibility for the code. You are free to use and/or modify and/or distribute any or all code posted on the Java Tips Weblog without restriction. A credit in the code comments would be nice, but not in any way mandatory.

EDIT: I realize HSB != HSL, the answer below is for HSB.
I don't think there is any need to use ColorSpaces here. Try something like the following:
float hue = 0.9f; //hue
float saturation = 1.0f; //saturation
float brightness = 0.8f; //brightness
Color myRGBColor = Color.getHSBColor(hue, saturation, brightness);

Here is a simple implementation that will return a Color based on hue, saturation, and lightness values from 0.0 to 1.0...
static public Color hslColor(float h, float s, float l) {
float q, p, r, g, b;
if (s == 0) {
r = g = b = l; // achromatic
} else {
q = l < 0.5 ? (l * (1 + s)) : (l + s - l * s);
p = 2 * l - q;
r = hue2rgb(p, q, h + 1.0f / 3);
g = hue2rgb(p, q, h);
b = hue2rgb(p, q, h - 1.0f / 3);
}
return new Color(Math.round(r * 255), Math.round(g * 255), Math.round(b * 255));
}
EDIT by Yona-Appletree:
I found what I think is the correct hue2rgb function and tested it as working:
private static float hue2rgb(float p, float q, float h) {
if (h < 0) {
h += 1;
}
if (h > 1) {
h -= 1;
}
if (6 * h < 1) {
return p + ((q - p) * 6 * h);
}
if (2 * h < 1) {
return q;
}
if (3 * h < 2) {
return p + ((q - p) * 6 * ((2.0f / 3.0f) - h));
}
return p;
}

I found the built-in method for HSB (which is not the same as HSL, but is similar)
[Color.getHSBColor(float h, float s, float b)](http://docs.oracle.com/javase/7/docs/api/java/awt/Color.html#getHSBColor(float,%20float,%20float))

Maybe this will help. The JDK doesn't seem to be very helpful when wanting to use colors in another color space.
Edit: In ColorSpace.getName(idx) there's this little snippet:
case ColorSpace.TYPE_HLS:
compName = new String[] {"Hue", "Lightness",
"Saturation"};
so it was what you thought, but looking at the type hierarchy of ColorSpace it doesn't seem to be used or implemented in any way anywhere. ColorSpace is extended by only two other classes BogusColorSpace and ICC_ColorSpace, so I'm guessing they're expecting developers to create their own implementations for different color spaces.

If your input is swing/awt widgets, then with Java 7 JColorChooser you can get Color by HSV and HSL spaces. http://java.dzone.com/articles/new-color-chooser-jdk-7

Change the alpha value of a BufferedImage?

How do I change the global alpha value of a BufferedImage in Java? (I.E. make every pixel in the image that has a alpha value of 100 have a alpha value of 80)

#Neil Coffey:
Thanks, I've been looking for this too; however, Your code didn't work very well for me (white background became black).
I coded something like this and it works perfectly:
public void setAlpha(byte alpha) {
alpha %= 0xff;
for (int cx=0;cx<obj_img.getWidth();cx++) {
for (int cy=0;cy<obj_img.getHeight();cy++) {
int color = obj_img.getRGB(cx, cy);
int mc = (alpha << 24) | 0x00ffffff;
int newcolor = color & mc;
obj_img.setRGB(cx, cy, newcolor);
}
}
}
Where obj_img is BufferedImage.TYPE_INT_ARGB.
I change alpha with setAlpha((byte)125); alpha range is now 0-255.
Hope someone finds this useful.

I don't believe there's a single simple command to do this. A few options:
copy into another image with an AlphaComposite specified (downside: not converted in place)
directly manipulate the raster (downside: can lead to unmanaged images)
use a filter or BufferedImageOp
The first is the simplest to implement, IMO.

This is an old question, so I'm not answering for the sake of the OP, but for those like me who find this question later.
AlphaComposite
As #Michael's excellent outline mentioned, an AlphaComposite operation can modify the alpha channel. But only in certain ways, which to me are somewhat difficult to understand:
is the formula for how the "over" operation affects the alpha channel. Moreover, this affects the RGB channels too, so if you have color data that needs to be unchanged, AlphaComposite is not the answer.
BufferedImageOps
LookupOp
There are several varieties of BufferedImageOp (see 4.10.6 here). In the more general case, the OP's task could be met by a LookupOp, which requires building lookup arrays. To modify only the alpha channel, supply an identity array (an array where table[i] = i) for the RGB channels, and a separate array for the alpha channel. Populate the latter array with table[i] = f(i), where f() is the function by which you want to map from old alpha value to new. E.g. if you want to "make every pixel in the image that has a alpha value of 100 have a alpha value of 80", set table[100] = 80. (The full range is 0 to 255.) See how to increase opacity in gaussian blur for a code sample.
RescaleOp
But for a subset of these cases, there is a simpler way to do it, that doesn't require setting up a lookup table. If f() is a simple, linear function, use a RescaleOp. For example, if you want to set newAlpha = oldAlpha - 20, use a RescaleOp with a scaleFactor of 1 and an offset of -20. If you want to set newAlpha = oldAlpha * 0.8, use a scaleFactor of 0.8 and an offset of 0. In either case, you again have to provide dummy scaleFactors and offsets for the RGB channels:
new RescaleOp({1.0f, 1.0f, 1.0f, /* alpha scaleFactor */ 0.8f},
{0f, 0f, 0f, /* alpha offset */ -20f}, null)
Again see 4.10.6 here for some examples that illustrate the principles well, but are not specific to the alpha channel.
Both RescaleOp and LookupOp allow modifying a BufferedImage in-place.

for a nicer looking alpha change effect, you can use relative alpha change per pixel (rather than static set, or clipping linear)
public static void modAlpha(BufferedImage modMe, double modAmount) {
//
for (int x = 0; x < modMe.getWidth(); x++) {
for (int y = 0; y < modMe.getHeight(); y++) {
//
int argb = modMe.getRGB(x, y); //always returns TYPE_INT_ARGB
int alpha = (argb >> 24) & 0xff; //isolate alpha
alpha *= modAmount; //similar distortion to tape saturation (has scrunching effect, eliminates clipping)
alpha &= 0xff; //keeps alpha in 0-255 range
argb &= 0x00ffffff; //remove old alpha info
argb |= (alpha << 24); //add new alpha info
modMe.setRGB(x, y, argb);
}
}
}

I'm 99% sure the methods that claim to deal with an "RGB" value packed into an int actually deal with ARGB. So you ought to be able to do something like:
for (all x,y values of image) {
int argb = img.getRGB(x, y);
int oldAlpha = (argb >>> 24);
if (oldAlpha == 100) {
argb = (80 << 24) | (argb & 0xffffff);
img.setRGB(x, y, argb);
}
}
For speed, you could maybe use the methods to retrieve blocks of pixel values.

You may need to first copy your BufferedImage to an image of type BufferedImage.TYPE_INT_ARGB. If your image is of type, say, BufferedImage.TYPE_INT_RGB, then the alpha component won't be set correctly. If your BufferedImage is of type BufferedImage.TYPE_INT_ARGB, then the code below works.
/**
* Modifies each pixel of the BufferedImage so that the selected component (R, G, B, or A)
* is adjusted by delta. Note: the BufferedImage must be of type BufferedImage.TYPE_INT_ARGB.
* #param src BufferedImage of type BufferedImage.TYPE_INT_ARGB.
* #param colorIndex 0=red, 1=green, 2=blue, 3= alpha
* #param delta amount to change component
* #return
*/
public static BufferedImage adjustAColor(BufferedImage src,int colorIndex, int delta) {
int w = src.getWidth();
int h = src.getHeight();
assert(src.getType()==BufferedImage.TYPE_INT_ARGB);
for (int y = 0; y < h; y++)
for (int x = 0; x < w; x++) {
int rgb = src.getRGB(x,y);
java.awt.Color color= new java.awt.Color(rgb,true);
int red=color.getRed();
int green=color.getGreen();
int blue=color.getBlue();
int alpha=color.getAlpha();
switch (colorIndex) {
case 0: red=adjustColor(red,delta); break;
case 1: green=adjustColor(green,delta); break;
case 2: blue=adjustColor(blue,delta); break;
case 3: alpha=adjustColor(alpha,delta); break;
default: throw new IllegalStateException();
}
java.awt.Color adjustedColor=new java.awt.Color(red,green,blue,alpha);
src.setRGB(x,y,adjustedColor.getRGB());
int gottenColorInt=src.getRGB(x,y);
java.awt.Color gottenColor=new java.awt.Color(gottenColorInt,true);
assert(gottenColor.getRed()== red);
assert(gottenColor.getGreen()== green);
assert(gottenColor.getBlue()== blue);
assert(gottenColor.getAlpha()== alpha);
}
return src;
}
private static int adjustColor(int value255, int delta) {
value255+= delta;
if (value255<0) {
value255=0;
} else if (value255>255) {
value255=255;
}
return value255;
}