sampling image files / rgb / arrays / export

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blueloom0..

sampling image files / rgb / arrays / export

in Programming Questions • 2 years ago

sampling image files

hi,

I think I am sort of halfway there :
reading out all the the R - G - B values for every pixel in a series of image files. See below.

I have a few questions though:

- it's incredibly slow - any way to improve performance?

- I am writing the values in a array of type "float" - how can I save this array to a text file / and ideally put a comma in between the values for separation?

- can I convert the array to a (very long) string ?

thanks a lot for any help,

Peter

-----------------------------------------------------------------------

PImage img;

void setup() {

size(360, 240);

//img = loadImage("test.jpg");

// image(img,0,0);

}

void draw() {

float[] numbers = new float[50000000];

numbers[0]=0;

for (int i = 0; i < 1; i ++ ) {

img = loadImage( "test" + i + ".jpg" );

img.loadPixels();

image(img,0,0);

// Since we are going to access the image's pixels too

for (int y = 0; y < height; y++) {

for (int x = 0; x < width; x++) {

int loc = x + y*width;

// The functions red(), green(), and blue() pull out the 3 color components from a pixel.

float r = red(img.pixels[loc]);

float g = green(img.pixels[loc]);

float b = blue(img.pixels[loc]);

append(numbers,r);

//append(numbers,500)

append(numbers,g);

append(numbers,b);

println(r);

println(loc);

// Set the display pixel to the image pixel

// pixels[loc] = color(r,g,b);

}

//updatePixels();

/// write values to array (csv) plus at a seperator marker at the end to distinguish files

//saveStrings("numbers.dat", pixels);

append(numbers,600)

}

/// send array to udp or textfile

saveBytes("numbers.dat", numbers);

//saveStrings("nouns.txt", list);

}

Replies(6)

PhiLho

Re: sampling image files / rgb / arrays / export

2 years ago

" - it's incredibly slow - any way to improve performance?"
Yes. Just avoid loading an image (even less several!) on each frame!

"save & convert"
What is your final goal?

blueloom0..

Re: Re: sampling image files / rgb / arrays / export

2 years ago

hi,

thanks. I wasn't aware I am loading several images at a time.

Could you point out where that is happening?

The goal is to :

- load a series of images from a folder test0, test1 ....

- read out the red - green - and blue values for every pixel and every file, seperated by comma, files by ; (for example)

- export those values into a text file

I am looking to re-import that text file into grasshopper for rhino and build 3D geometry with them

thanks,

Peter

calsign

Re: sampling image files / rgb / arrays / export

2 years ago

Your program has several bugs, but to answer some of your questions...

SaveStrings() should help with saving...
To convert to a String, you would call str() to the array...
And adding commas (and spaces)

String[] s = new String[pixels.length];
for(int i = 0; i < s.length; i ++) {
s[i] = str(pixels[i]) + ", ";
}
saveStrings("numbers.dat", pixels);

That should work, you get the idea

To convert it to a really long String, (there might be function for this) you just go through the array with a for loop and add each element to a String.

Ask if you want clarification.
I hope this helped

PhiLho

Re: sampling image files / rgb / arrays / export

2 years ago

Your code is OK (with regard to loading images) if you add noLoop() to setup(), so that draw() is called only once.
I see also (looking closer...) that you used append(), which is also very slow. And you are supposed to use the result of the function, anyway.
Actually, you don't need to store the numbers in an array. You can convert them directly to string, as calsign said, except I would use a StringBuilder, much faster for repeated appends.

blueloom0..

Re: sampling image files / rgb / arrays / export

2 years ago

thank you all for your tips!

got it to work finally - and pretty fast now :

PImage img;
PrintWriter output;

void setup() {
size(360, 240);
output = createWriter("rgbvalues.txt");

}

void draw() {
    float[] numbers = new float[5000000];
    numbers[0]=0;

for (int i = 0; i < 2; i ++ ) {
    img = loadImage( "test" + i + ".jpg" );
    img.loadPixels();
    image(img,0,0);

    output.println("Image "+i);
    output.println();
    for (int y = 0; y < height; y++) {
      for (int x = 0; x < width; x++) {
        int loc = x + y*width;
        float r = red(img.pixels[loc]);
        float g = green(img.pixels[loc]);
        float b = blue(img.pixels[loc]);

        output.println(int(r) + "," + int(g) + "," + int(b));
      }
    }

    output.println();
}

output.flush(); // Writes the remaining data to the file
output.close(); // Finishes the file
exit();

}

thanks,

Peter

digitalte..

Re: sampling image files / rgb / arrays / export

2 years ago

If you still want it faster, instead of using float r = red(img.pxels[loc]...you can use

int r = img.pixels[loc]>>16 & 0xFF;

int b = img.pixels[loc]>>8 & 0xFF;

int g = img.pixels[loc] & 0xFF;

This is basically a shortcut to access the pixel data more efficiently. I read about this a while ago in the processing reference, and it has helped me a lot. It also means you don't have to convert each value to int, I'm pretty sure.

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