saveBytes/loadBytes performance

Programming Questions

zahand

saveBytes/loadBytes performance

in Programming Questions • 6 months ago

I'm using the following function to write an image's pixel array to a temp file and then read them back into the array.

void setup() {
img = loadImage("image.png");
}
void keyPressed() {
if (key == 's') {
int t = millis();
saveRAW("x.dat");
println(millis()-t);
}
if (key == 'd') {
int t = millis();
loadRAW("x.dat");
println(millis()-t);
}
}
void saveRAW(String filename) {
byte[] bytes = new byte[img.pixels.length*3];
int index = 0;
for (int i = 0; i < bytes.length; i++) {
int c = img.pixels[index];
bytes[i++] = (byte)((c >> 16) & 0xff);
bytes[i++] = (byte)((c >> 8) & 0xff);
bytes[i] = (byte)(c & 0xff);
index++;
}
saveBytes(filename, bytes);
}
void loadRAW(String filename) {
byte[] bytes = loadBytes(filename);
int index = 0;
int count = bytes.length/3;
for (int i = 0; i<count; i++) {
img.pixels[i] =
0xFF000000 |
(bytes[index++] & 0xff) << 16 |
(bytes[index++] & 0xff) << 8 |
(bytes[index++] & 0xff);
}
}

I'm getting ~6ms on saveRaw and ~36ms on loadRAW. Can someone please clarify why loadRAW is so much slower? I mean are the two functions not pretty similar?

Does it have to do with saveBytes and loadBytes or the rest of the function I've written? Is it possible to make it any faster?

Replies(2)

GoToLoop

Re: saveBytes/loadBytes performance

6 months ago

Tried to tweak it but no success.

Anyways, my speed here is about 4ms reading & 20ms loading after they got warmed up.

PImage img;

void setup() {
  img = loadImage("image.png");
  img.loadPixels();

  size(img.width, img.height);
  noLoop();

  keyCode = 'S';
  keyPressed();
}

void draw() {
  background(img);
}

void keyPressed() {
  redraw();

  final int k = keyCode, t = millis();

  if (k == 'S')                    saveRAW("x.dat");
  else if (k == 'D' | k == 'L')    loadRAW("x.dat");

  print( (char) k + " - " + (millis() - t) + " | \t");
}

void saveRAW(String filename) {
  byte[] bytes = new byte[img.pixels.length * 3];

  for (int c, idx = 0, i = 0; i != bytes.length;) {
    c = img.pixels[idx++];

    bytes[i++] = (byte) (c >> 020 & 255);
    bytes[i++] = (byte) (c >> 010 & 255);
    bytes[i++] = (byte) (c & 255);
  }

  saveBytes(filename, bytes);
}

void loadRAW(String filename) {
  byte[] bytes = loadBytes(filename);
  int count = bytes.length / 3;

  for (int i = 0, idx = 0; idx != count;)
    img.pixels[idx++] = 
      (bytes[i++] & 255) << 020 |
      (bytes[i++] & 255) << 010 |
      (bytes[i++] & 255) | #000000;
}

PhiLho

Re: saveBytes/loadBytes performance

6 months ago

Since we know upfront the size of the data to read, this is a bit faster:

import java.io.*;
PImage img;
int imageSize;
void setup() {
img = loadImage("G:/Images/foret_0003_1024.jpg");
imageSize = img.pixels.length * 3;
}
void draw() { }
void keyPressed() {
if (key == 's') {
int t = millis();
saveRAW("x.dat");
println(millis()-t);
}
if (key == 'd') {
int t = millis();
loadRAW("x.dat");
println(millis()-t);
}
}
void saveRAW(String filename) {
byte[] bytes = new byte[imageSize];
int index = 0;
for (int i = 0; i < bytes.length; i++) {
int c = img.pixels[index];
bytes[i++] = (byte)((c >> 16) & 0xff);
bytes[i++] = (byte)((c >> 8) & 0xff);
bytes[i] = (byte)(c & 0xff);
index++;
}
saveBytes(filename, bytes);
}
void loadRAW(String filename) {
byte[] bytes = loadBytes(filename, imageSize);
int index = 0;
int count = bytes.length/3;
for (int i = 0; i<count; i++) {
img.pixels[i] =
0xFF000000 |
bytes[index++] << 16 |
bytes[index++] << 8 |
bytes[index++];
}
}
// Taken from Processing code, just adding a size parameter
byte[] loadBytes(String filename, int size) {
InputStream is = createInput(filename);
if (is != null) {
byte[] outgoing = loadBytes(is, size);
try {
is.close();
}
catch (IOException e) {
e.printStackTrace(); // shouldn't happen
}
return outgoing;
}
System.err.println("The file \"" + filename + "\" " +
"is missing or inaccessible, make sure " +
"the URL is valid or that the file has been " +
"added to your sketch and is readable.");
return null;
}
byte[] loadBytes(InputStream input, int size) {
try {
BufferedInputStream bis = new BufferedInputStream(input);
ByteArrayOutputStream out = new ByteArrayOutputStream(size);
int c = bis.read();
while (c != -1) {
out.write(c);
c = bis.read();
}
return out.toByteArray();
}
catch (IOException e) {
e.printStackTrace();
//throw new RuntimeException("Couldn't load bytes from stream");
}
return null;
}