Develop Reference

Remove Background of an Image, Split it in same sizes and Change color(overlay)

I've been searching the internet for changing colour or overlaying a specific part of a bitmap. I've a square bitmap and I want to change the colour in a matrix pattern that is in equal 9 blocks which can be understood from the following image. (Cyan colour line here is for demonstration only)
I've read about boundary fill algorithm in College but here for java, I came to know that it is too bulky to perform such an operation for 9 specific parts. And I don't know how to use Paint with Canvas for such a square scenario.
So is there a method or something which can help me figure out how to paint a specific square by providing the size or location without performing a huge task on UI.
Here's what I need to achieve:
I can change the color, location,size by myself if there's something which can help me out.
Also, as there is white background, is there a way to not paint the background or do I have to use PNG?
Update:
I'm successfully able to divide the image in 9 equal parts using following code but PorterDuffColorFilter is not working as expected.
Code:
public void splitBitmap(Bitmap bitmap) {
int width, height;
// Divide the original bitmap width by the desired vertical column count
width = bitmap.getWidth() / 3;
// Divide the original bitmap height by the desired horizontal row count
height = bitmap.getHeight() / 3;
// Loop the array and create bitmaps for each coordinate
for (int x = 0; x < 3; ++x) {
for (int y = 0; y < 3; ++y) {
// Create the sliced bitmap
smallimages.add(Bitmap.createBitmap(bitmap, x * width, y * height, width, height));
}
}
Intent intent = new Intent(this, MainActivity.class);
startActivity(intent);
}
The above code provides 9 bitmaps which then set to a GridLayout. But No mode of PorterDuffColorFilter is useful. Either the images remain original or is painted completely. I've tried every one of the modes available and none worked.

I've done something similar to this so after changing my code a bit, I think this is what you want:
Assuming that you don't have PNG,
First, remove the white background from your image Source:
Setting the white color as Transparent, you can use any color you want.
private static final int[] FROM_COLOR = new int[]{255, 255, 255};
private static final int THRESHOLD = 3;
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.test_colors);
ImageView iv = (ImageView) findViewById(R.id.img);
Drawable d = getResources().getDrawable(RES);
iv.setImageDrawable(adjust(d));
}
private Drawable adjust(Drawable d)
{
int to = Color.TRANSPARENT;
//Need to copy to ensure that the bitmap is mutable.
Bitmap src = ((BitmapDrawable) d).getBitmap();
Bitmap bitmap = src.copy(Bitmap.Config.ARGB_8888, true);
for(int x = 0;x < bitmap.getWidth();x++)
for(int y = 0;y < bitmap.getHeight();y++)
if(match(bitmap.getPixel(x, y)))
bitmap.setPixel(x, y, to);
return new BitmapDrawable(bitmap);
}
private boolean match(int pixel)
{
//There may be a better way to match, but I wanted to do a comparison ignoring
//transparency, so I couldn't just do a direct integer compare.
return Math.abs(Color.red(pixel) - FROM_COLOR[0]) < THRESHOLD &&
Math.abs(Color.green(pixel) - FROM_COLOR[1]) < THRESHOLD &&
Math.abs(Color.blue(pixel) - FROM_COLOR[2]) < THRESHOLD;
}
Above code will change the color to transparent and below code will split the bitmap into 9 same size bitmaps:
public void splitBitmap(Bitmap bitmap) {
ArrayList<Bitmap> smallimages = new ArrayList<>(9);
int width, height;
// Divide the original bitmap width by the desired vertical column count
width = bitmap.getWidth() / 3;
// Divide the original bitmap height by the desired horizontal row count
height = bitmap.getHeight() / 3;
// Loop the array and create bitmaps for each coordinate
for (int x = 0; x < 3; ++x) {
for (int y = 0; y < 3; ++y) {
// Create the sliced bitmap
smallimages.add(Bitmap.createBitmap(bitmap, x * width, y * height, width, height));
}
}
}
At last, you can use PorterDuffColorFilter on every bitmap:
imageView.setImageDrawable(arrayList.get(0));
imageView.setColorFilter(Color.BLACK, PorterDuff.Mode.SRC_ATOP);
There can be problems as it works for me and might not for you but this is the way you can achieve your needed result.
If any problem persists, I can help.

Android: Repeatedly drawing many small shapes efficiently and accurately

I am working on a project in Android that builds Abelian Sandpiles (a type of 2D cellular Automaton). I have a grid of cells (that starts out small but later grows) and I'm drawing square (or circles) on the grid to show the state of each cell. At each step, I update usually less than 30% of the cells.
My basic approach is taken from this post: Android: How to get a custom view to redraw partially?
I draw all the shapes to the canvas and cache it as a bitmap, then at each step I update only the cells that need updating, then cache the result and repeat. This works well enough when the grid is fairly small (less than 50 x 50), but becomes increasingly unsatisfactory as the grid size increase. The problems are that
1) it is too slow when the number of updates becomes high
2) even when it runs smoothly, the drawing doesn't look clean - e.g., a line of small rectangles looks quite choppy and inconsistent (see image).
I am sure that there must be a better way to approach this problem. With a larger grid (e.g., 150 x 150), I'm drawing rects or circles with a width of ~2.33, and this can't be optimal. Any advice for improving performance and/or image quality?
Simplified drawing code is here:
#Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
if (ready) {
if (needsCompleteRedraw) {
this.cachedBitmap = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888);
cacheCanvas = new Canvas(this.cachedBitmap);
doInitialDrawing(cacheCanvas);
canvas.drawBitmap(this.cachedBitmap, 0, 0, null);
needsCompleteRedraw = false;
} else {
canvas.drawBitmap(this.cachedBitmap, 0, 0, null);
doPartialRedraws(cacheCanvas);
}
}
}
private void doInitialDrawing(Canvas clean) {
for (int i = 0; i < pile.gridHeight; i++) {
for (int j = 0; j < pile.gridWidth; j++) {
int state = pile.getGridValueAtPoint(new Point(j, i ));
clean.drawRect(j * cellSize, i * cellSize, (j + 1 )* cellSize, (i + 1) * cellSize, paints[state]);
}
}
}
private void doPartialRedraws(Canvas cached) {
for (Point p : pile.needsUpdateSet) {
int state = pile.getGridValueAtPoint(p);
cached.drawRect(p.x * cellSize, p.y * cellSize, (p.x + 1 )* cellSize, (p.y + 1) * cellSize, paints[state]);
}
pile.needsUpdateSet = new HashSet<Point>();
}
and my paint objects are set with antialias as true, and I've tried setting the style to both FILL and FILL_AND_STROKE.
Any suggestions would be much appreciated.

Ok. Several problems here.
1)Don't ever create a canvas in onDraw. If you think you need to, you haven't architected your drawing code correctly.
2)The point of doing draws to a cache bitmap is NOT to draw the cache in onDraw, but to do it on its own thread- or at least not at draw time.
You should have a second thread that draws to the cached bitmap on demand, then calls postInvalidate() on the view. The onDraw function should only be a call to drawBitmap, drawing the cached bitmap to the screen.

Library for android for Google cardboard barrel distortion

I am trying to implement a 3D app for Android that should also support cardboard like viewers. I have seen some of those images and they seem to have some kind of barrel distortion in order to be orthogonal through the cardboard lenses.
So I was looking for algorithms or libraries specifically for Java/Android that would help me achieving this.
I have found this implementation: http://www.helviojunior.com.br/fotografia/barrel-and-pincushion-distortion/
It would be great to have something like this because it has everything I'd need. Unfortunately it's for C# and it has some specific code that I just couldn't easily translate into more generic code.
Then there is a simpler Java implementation here: http://popscan.blogspot.de/2012/04/fisheye-lens-equation-simple-fisheye.html
I have changed it to:
public static Bitmap fisheye(Bitmap srcimage) {
/*
* Fish eye effect
* tejopa, 2012-04-29
* http://popscan.blogspot.com
* http://www.eemeli.de
*/
// get image pixels
double w = srcimage.getWidth();
double h = srcimage.getHeight();
int[] srcpixels = new int[(int)(w*h)];
srcimage.getPixels(srcpixels, 0, (int)w, 0, 0, (int)w, (int)h);
Bitmap resultimage = srcimage.copy(srcimage.getConfig(), true);
// create the result data
int[] dstpixels = new int[(int)(w*h)];
// for each row
for (int y=0;y<h;y++) {
// normalize y coordinate to -1 ... 1
double ny = ((2*y)/h)-1;
// pre calculate ny*ny
double ny2 = ny*ny;
// for each column
for (int x=0;x<w;x++) {
// preset to black
dstpixels[(int)(y*w+x)] = 0;
// normalize x coordinate to -1 ... 1
double nx = ((2*x)/w)-1;
// pre calculate nx*nx
double nx2 = nx*nx;
// calculate distance from center (0,0)
// this will include circle or ellipse shape portion
// of the image, depending on image dimensions
// you can experiment with images with different dimensions
double r = Math.sqrt(nx2+ny2);
// discard pixels outside from circle!
if (0.0<=r&&r<=1.0) {
double nr = Math.sqrt(1.0-r*r);
// new distance is between 0 ... 1
nr = (r + (1.0-nr)) / 2.0;
// discard radius greater than 1.0
if (nr<=1.0) {
// calculate the angle for polar coordinates
double theta = Math.atan2(ny,nx);
// calculate new x position with new distance in same angle
double nxn = nr*Math.cos(theta);
// calculate new y position with new distance in same angle
double nyn = nr*Math.sin(theta);
// map from -1 ... 1 to image coordinates
int x2 = (int)(((nxn+1)*w)/2.0);
// map from -1 ... 1 to image coordinates
int y2 = (int)(((nyn+1)*h)/2.0);
// find (x2,y2) position from source pixels
int srcpos = (int)(y2*w+x2);
// make sure that position stays within arrays
if (srcpos>=0 & srcpos < w*h) {
// get new pixel (x2,y2) and put it to target array at (x,y)
dstpixels[(int)(y*w+x)] = srcpixels[srcpos];
}
}
}
}
}
resultimage.setPixels(dstpixels, 0, (int)w, 0, 0, (int)w, (int)h);
//return result pixels
return resultimage;
}
But it doesn't have this lens factor, so the resulting image is always a full circle/ellipse.
Any chance you could point me to some working Java code or library or (maybe even better) help me to amend this code for the lens factor to be taken into account (0.0 <= factor <= 1.0)?

I managed to get it to work.
Bottom line: I created a Bitmap bigger than the original Bitmap, and then I drew the original Bitmap on the new Bitmap (and centered it there) using
Canvas canvas = new Canvas(newBitmap);
canvas.drawBitmap(originalBitmap, null, new Rect(x, y, r, b), null);
I used the Java algorithm posted in my question to create the effect on the new Bitmap. That worked great.

LibGDX texture bleeding issue

I'm new to LibGDX and was trying to implement parallax background.
Everything went good until I faced such issue: I get some stripes when scrolling background. You can see it in attached image:
So I looked deeper into an issue and figured out that this some sort of texture bleeding. But the case is that my textures already have [Linear, Nearest] filter set and TexturePacker uses duplicatePadding. Actually, I don't know any other methods to solve this issue. Please help!
Here's some of my code:
TexturePacker
TexturePacker.Settings settings = new TexturePacker.Settings();
settings.minWidth = 256;
settings.minHeight = 256;
settings.duplicatePadding = true;
TexturePacker.process(settings, "../../design", "./", "textures");
AssetLoader
textureAtlas = new TextureAtlas(Gdx.files.internal("textures.atlas"));
for (int i = 0; i < 2; i++) {
Background.skies.add(textureAtlas.findRegion("background/sky", i));
Background.skies.get(i).getTexture().setFilter(Texture.TextureFilter.Linear, Texture.TextureFilter.Nearest);
}
for (int i = 0; i < 2; i++) {
Background.clouds.add(textureAtlas.findRegion("background/cloud", i));
Background.clouds.get(i).getTexture().setFilter(Texture.TextureFilter.Linear, Texture.TextureFilter.Nearest);
}
for (int i = 0; i < 8; i++) {
Background.cities.add(textureAtlas.findRegion("background/city", i));
Background.cities.get(i).getTexture().setFilter(Texture.TextureFilter.Linear, Texture.TextureFilter.Nearest);
}
Background.moon = textureAtlas.findRegion("background/moon");
Background.forest = textureAtlas.findRegion("background/forest");
Background.road = textureAtlas.findRegion("background/road");
Background.moon.getTexture().setFilter(Texture.TextureFilter.Linear, Texture.TextureFilter.Nearest);
Background.forest.getTexture().setFilter(Texture.TextureFilter.Linear, Texture.TextureFilter.Nearest);
Background.road.getTexture().setFilter(Texture.TextureFilter.Linear, Texture.TextureFilter.Nearest);
BackgroundDrawer
private void drawParallaxTextureList(Batch batch, List<TextureAtlas.AtlasRegion> list,
float moveX, float posY) {
for (int i = 0; i < list.size(); i++) {
boolean needDraw = false;
float shift = GameScreen.VIEWPORT_WIDTH * i;
float drawX = 0.0f;
if (shift - moveX <= -(GameScreen.VIEWPORT_WIDTH)) { // If it's behind the screen
if (i == 0) { // If it's first element
if (moveX >= GameScreen.VIEWPORT_WIDTH * (list.size() - 1)) { // We need to show first after last
needDraw = true;
drawX = (GameScreen.VIEWPORT_WIDTH) - (moveX - ((GameScreen
.VIEWPORT_WIDTH) * (list.size() - 1)));
}
}
} else if (shift - moveX < (GameScreen.VIEWPORT_WIDTH - 1)) {
needDraw = true;
drawX = shift - moveX;
}
if (needDraw) {
batch.draw(list.get(i), (int) drawX, (int) posY);
}
}
}
NOTE: I don't use any camera for drawing right now. I only use FitViewport with size of 1920x1280. Also, bleeding sometimes appears even in FullHD resolution.
UPDATE: Setting both Nearest filters for minification and magification with increasing paddingX and disabling antialiasing solved issue, but final image become too ugly! Is there way to avoid disabling antialiasing? Because without it, downscale look awful.

Try to set both min and mag filters as Nearest
.setFilter(Texture.TextureFilter.Nearest, Texture.TextureFilter.Nearest);
In GUI TexturePacker there is an option to extrude graphics - it means repeating every of border pixel of texture. Then you can set both filters to Linear
.setFilter(Texture.TextureFilter.Linear, Texture.TextureFilter.Linear);
but unfortunately I cannot see this option in the TexturePacker.Settings object you are using. You can try to set Linear to both but I'm pretty sure it won't be working (Linear filter takes nearest 4 texels to generate the one so it will probably still generate issues).
Try to use GUI Texturepacker then with extrude option maybe

A few possible reasons for this artifact:
Maybe the padding is not big enough when the sprite resolution is shrunk down. Try changing your texture packer's filterMin to MipMapLinearNearest. And also try increasing the size of paddingX and paddingY.
Maybe you're seeing dim or brightened pixels at the edge of your sprite because you're not using pre-multiplied alpha and your texture's background color (where its alpha is zero) is white. Try setting premultiplyAlpha: true. If you do this, you need to also change the SpriteBatch's blend function to (GL20.GL_ONE, GL20.GL_ONE_MINUS_SRC_ALPHA) to render properly.
You seem to be rounding your sprite positions and sizes to integers when you draw them. This would work in a pixel perfect game, where you're sure the sprites are being rendered exactly at 1:1 resolution to the screen. But once the screen size does not match exactly, your rounding might produce gaps that are less than 1 pixel wide, which will look like semi-transparent pixels.

Android: How to do this framing paint?

I Have Some static images like below:
Now, I want is, when i touch on the face or hand, then the selected color should be fill on that skin portion.
See below image of result:
So how to get the result like above ??
Redo and Undo Functionality Should be also there.
I have try with the FloodFill color but doing that i can only able to do color in to the perticular portion. as FloodFill only fill the color till the same pixwl color comes. If the touch place pixel color get change the it will not fill color on it.
So Usinf FloodFill i got the result like below image, If i press on the hand, then only hand portion will fill with color, instead of it i want to fill color to the other hand and face also.
So Please help me in this case.
EDITED
After some reply i got the solution like this one.
But still there is a memory issue. It consume lots of memory to draw the color. So please can anyone help me for it ?

You can have a complete image colored the actual way and when you fill a certain region with a color, it will replace all the regions that is specified by that color to be filled in.
Layman's terms:
User will click on the hand of the OUTLINE
That click location will be checked with another image with perfectly color coded regions. Lets call it a MASK for this case. All the skin regions will have the same color. The shirt areas will be another color.
Wherever the user clicks, the selected color by the user will be applied to every pixel that has that similar color in the MASK, but instead of painting directly on the MASK, you paint onto the pixels of the the OUTLINE.
I hope this helps.
Feel free to comment if you want an example and then I can update the answer with that, but I think you can get it from here.
EDIT:
Basically start off with a simple image like this. This we can call as OUTLINE
Then as the developer, you have to do some work. Here, you color code the OUTLINE. The result we call a MASK. To make this we, color code the regions with the same color that you want. This can be done on paint or whatever. I used Photoshop to be cool lol :D.
Then there is the ALGORITHM to get it working on the phone. Before you read the code, look at this variable.
int ANTILAISING_TOLERANCE = 70; //Larger better coloring, reduced sensing
If you zoom up on the image specifically noting the black regions of the border, you can actually see that sometimes, the computer blends the colors a little bit. In order to account for that change, we use this tolerance value.
COLORINGANDROIDACTIVITY.JAVA
package mk.coloring;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.widget.ImageView;
import android.view.View.OnTouchListener;
public class ColoringAndroidActivity extends Activity implements OnTouchListener{
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
findViewById(R.id.imageView1).setOnTouchListener(this);
}
int ANTILAISING_TOLERANCE = 70;
public boolean onTouch(View arg0, MotionEvent arg1) {
Bitmap mask = BitmapFactory.decodeResource(getResources(), R.drawable.mask);
int selectedColor = mask.getPixel((int)arg1.getX(),(int)arg1.getY());
int sG = (selectedColor & 0x0000FF00) >> 8;
int sR = (selectedColor & 0x00FF0000) >> 16;
int sB = (selectedColor & 0x000000FF);
Bitmap original = BitmapFactory.decodeResource(getResources(), R.drawable.empty);
Bitmap colored = Bitmap.createBitmap(mask.getWidth(), mask.getHeight(), Config.ARGB_8888);
Canvas cv = new Canvas(colored);
cv.drawBitmap(original, 0,0, null);
for(int x = 0; x<mask.getWidth();x++){
for(int y = 0; y<mask.getHeight();y++){
int g = (mask.getPixel(x,y) & 0x0000FF00) >> 8;
int r = (mask.getPixel(x,y) & 0x00FF0000) >> 16;
int b = (mask.getPixel(x,y) & 0x000000FF);
if(Math.abs(sR - r) < ANTILAISING_TOLERANCE && Math.abs(sG - g) < ANTILAISING_TOLERANCE && Math.abs(sB - b) < ANTILAISING_TOLERANCE)
colored.setPixel(x, y, (colored.getPixel(x, y) & 0xFF000000) | 0x00458414);
}
}
((ImageView)findViewById(R.id.imageView1)).setImageBitmap(colored);
return true;
}
}
This code doesn't provide the user with much of color choices. Instead, if the user touches a region, it will look at the MASK and paint the OUTLINE accordingly. But, you can make really interesting and interactive.
RESULT
When I touched the man's hair, it not only colored the hair, but colored his shirt and hand with the same color. Compare it with the MASK to get a good idea of what happened.
This is just a basic idea. I have created multiple Bitmaps but there is not really a need for that. I had used it for testing purposes and takes up unnecessary memory. And you don't need to recreate the mask on every click, etc.
I hope this helps you :D
Good luck

Use a FloodFill Algorithm. Fill the complete canvas but keep the bound fill area as it is like circle, rectangle. You can also check this link. Android: How to fill color to the specific part of the Image only?. The general idea get the x and y co-ordinates on click.
final Point p1 = new Point();
p1.x=(int) x; p1.y=(int) y; X and y are co-ordinates when user clicks on the screen
final int sourceColor= mBitmap.getPixel((int)x,(int) y);
final int targetColor =mPaint.getColor();
new TheTask(mDrawingManager.mDrawingUtilities.mBitmap, p1, sourceColor, targetColor).execute(); //Use AsyncTask and do floodfillin the doinBackground().
Check the above links for floodfill algorithmin android. This should help you achieve what you want. Android FingerPaint Undo/Redo implementation. This should help you modify according to your needs regarding undo and redo.
Edit:
A post on stackoverflow led me to a efficient way of using flood fill algorithm without delay and OOM.
Picking from the SO Post
Filling a small closed area works fine with the above flood fill algorithm. However for large area the algorithm works slow and consumes lot of memory. Recently i came across a post which uses QueueLinear Flood Fill which is way faster that the above.
Source :
http://www.codeproject.com/Articles/16405/Queue-Linear-Flood-Fill-A-Fast-Flood-Fill-Algorith
Code :
public class QueueLinearFloodFiller {
protected Bitmap image = null;
protected int[] tolerance = new int[] { 0, 0, 0 };
protected int width = 0;
protected int height = 0;
protected int[] pixels = null;
protected int fillColor = 0;
protected int[] startColor = new int[] { 0, 0, 0 };
protected boolean[] pixelsChecked;
protected Queue<FloodFillRange> ranges;
// Construct using an image and a copy will be made to fill into,
// Construct with BufferedImage and flood fill will write directly to
// provided BufferedImage
public QueueLinearFloodFiller(Bitmap img) {
copyImage(img);
}
public QueueLinearFloodFiller(Bitmap img, int targetColor, int newColor) {
useImage(img);
setFillColor(newColor);
setTargetColor(targetColor);
}
public void setTargetColor(int targetColor) {
startColor[0] = Color.red(targetColor);
startColor[1] = Color.green(targetColor);
startColor[2] = Color.blue(targetColor);
}
public int getFillColor() {
return fillColor;
}
public void setFillColor(int value) {
fillColor = value;
}
public int[] getTolerance() {
return tolerance;
}
public void setTolerance(int[] value) {
tolerance = value;
}
public void setTolerance(int value) {
tolerance = new int[] { value, value, value };
}
public Bitmap getImage() {
return image;
}
public void copyImage(Bitmap img) {
// Copy data from provided Image to a BufferedImage to write flood fill
// to, use getImage to retrieve
// cache data in member variables to decrease overhead of property calls
width = img.getWidth();
height = img.getHeight();
image = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565);
Canvas canvas = new Canvas(image);
canvas.drawBitmap(img, 0, 0, null);
pixels = new int[width * height];
image.getPixels(pixels, 0, width, 1, 1, width - 1, height - 1);
}
public void useImage(Bitmap img) {
// Use a pre-existing provided BufferedImage and write directly to it
// cache data in member variables to decrease overhead of property calls
width = img.getWidth();
height = img.getHeight();
image = img;
pixels = new int[width * height];
image.getPixels(pixels, 0, width, 1, 1, width - 1, height - 1);
}
protected void prepare() {
// Called before starting flood-fill
pixelsChecked = new boolean[pixels.length];
ranges = new LinkedList<FloodFillRange>();
}
// Fills the specified point on the bitmap with the currently selected fill
// color.
// int x, int y: The starting coords for the fill
public void floodFill(int x, int y) {
// Setup
prepare();
if (startColor[0] == 0) {
// ***Get starting color.
int startPixel = pixels[(width * y) + x];
startColor[0] = (startPixel >> 16) & 0xff;
startColor[1] = (startPixel >> 8) & 0xff;
startColor[2] = startPixel & 0xff;
}
// ***Do first call to floodfill.
LinearFill(x, y);
// ***Call floodfill routine while floodfill ranges still exist on the
// queue
FloodFillRange range;
while (ranges.size() > 0) {
// **Get Next Range Off the Queue
range = ranges.remove();
// **Check Above and Below Each Pixel in the Floodfill Range
int downPxIdx = (width * (range.Y + 1)) + range.startX;
int upPxIdx = (width * (range.Y - 1)) + range.startX;
int upY = range.Y - 1;// so we can pass the y coord by ref
int downY = range.Y + 1;
for (int i = range.startX; i <= range.endX; i++) {
// *Start Fill Upwards
// if we're not above the top of the bitmap and the pixel above
// this one is within the color tolerance
if (range.Y > 0 && (!pixelsChecked[upPxIdx])
&& CheckPixel(upPxIdx))
LinearFill(i, upY);
// *Start Fill Downwards
// if we're not below the bottom of the bitmap and the pixel
// below this one is within the color tolerance
if (range.Y < (height - 1) && (!pixelsChecked[downPxIdx])
&& CheckPixel(downPxIdx))
LinearFill(i, downY);
downPxIdx++;
upPxIdx++;
}
}
image.setPixels(pixels, 0, width, 1, 1, width - 1, height - 1);
}
// Finds the furthermost left and right boundaries of the fill area
// on a given y coordinate, starting from a given x coordinate, filling as
// it goes.
// Adds the resulting horizontal range to the queue of floodfill ranges,
// to be processed in the main loop.
// int x, int y: The starting coords
protected void LinearFill(int x, int y) {
// ***Find Left Edge of Color Area
int lFillLoc = x; // the location to check/fill on the left
int pxIdx = (width * y) + x;
while (true) {
// **fill with the color
pixels[pxIdx] = fillColor;
// **indicate that this pixel has already been checked and filled
pixelsChecked[pxIdx] = true;
// **de-increment
lFillLoc--; // de-increment counter
pxIdx--; // de-increment pixel index
// **exit loop if we're at edge of bitmap or color area
if (lFillLoc < 0 || (pixelsChecked[pxIdx]) || !CheckPixel(pxIdx)) {
break;
}
}
lFillLoc++;
// ***Find Right Edge of Color Area
int rFillLoc = x; // the location to check/fill on the left
pxIdx = (width * y) + x;
while (true) {
// **fill with the color
pixels[pxIdx] = fillColor;
// **indicate that this pixel has already been checked and filled
pixelsChecked[pxIdx] = true;
// **increment
rFillLoc++; // increment counter
pxIdx++; // increment pixel index
// **exit loop if we're at edge of bitmap or color area
if (rFillLoc >= width || pixelsChecked[pxIdx] || !CheckPixel(pxIdx)) {
break;
}
}
rFillLoc--;
// add range to queue
FloodFillRange r = new FloodFillRange(lFillLoc, rFillLoc, y);
ranges.offer(r);
}
// Sees if a pixel is within the color tolerance range.
protected boolean CheckPixel(int px) {
int red = (pixels[px] >>> 16) & 0xff;
int green = (pixels[px] >>> 8) & 0xff;
int blue = pixels[px] & 0xff;
return (red >= (startColor[0] - tolerance[0])
&& red <= (startColor[0] + tolerance[0])
&& green >= (startColor[1] - tolerance[1])
&& green <= (startColor[1] + tolerance[1])
&& blue >= (startColor[2] - tolerance[2]) && blue <= (startColor[2] + tolerance[2]));
}
// Represents a linear range to be filled and branched from.
protected class FloodFillRange {
public int startX;
public int endX;
public int Y;
public FloodFillRange(int startX, int endX, int y) {
this.startX = startX;
this.endX = endX;
this.Y = y;
}
}
}

One basic way would be something like the floodfill algorythm.
The Wikipedia article describes the algorythm and its variations pretty well.
Here you can find a implementation on SO. But depending on your specific needs this one has to be modified.