Numeric values from a pixel image

General Discussion Other

bensen_ger

Numeric values from a pixel image

in General Discussion • Other • 1 year ago

Hi there,

i am trying to obtain data from pixel Images.
I know its possible to read a line and obtain the r/g/b values of one specific pixel.
Still i can´t fully wrap my head around how to archive two things:

1. How can I assign a certain area within a picture (for example a square in the upper left of a png) to be read out?
2. How can I obtain data such as average gray value ?

I am just starting with processing so please bare with me if my question is somewhat stupid.
I am searching for days now and i just can´t seem to find any useful information.
Every help.. or link to tutorial would be much appreciated.

Thank you very much!

Replies(5)

amnon.owed

Re: Basic way of reading data from a pixel image

1 year ago

1. You can use get() to get a specific section of the image. Then you can do pixel operations on all the pixels of that section. Note that if you actually want to change the original pixels, you have to set() it back. Or do everything on the original pixel array in the first place of course (without get/set).

2. What do you mean with "average gray value"? To get started see: http://processing.org/learning/pixels/

bensen_ger

Re: Basic way of reading data from a pixel image

1 year ago

Thank you very much for the answer.

The goal of my question is:
I want to receive numeric values from pixel images wich I can then use as Integers/Floats.

Since all the pictures have the same size and are only black and white.. I thought it would be a good start to compare the average gray value ( how much black pixels are within that 100x100px image).
Is there a way to archive this?

PhiLho

Re: Numeric values from a pixel image

1 year ago

Have a look at pixels[]
It allows you to access to the color information of each pixel. With proper indexes, you can restrict the color reading from a given area of the image.
For gray level images, the R, G and B values are the same.
You can get the gray level with, for example:
int v = pixels[n] & 0xFF;
or
int v = pixels[n] % 255;
(will do the same thing).

amnon.owed

Re: Numeric values from a pixel image

1 year ago

See the above answers and links.

To count the black pixels compare each pixel's color to black and add 1 to a blackPixelCount variable. To find the average color of a greyscale image, add up the value of one color channel (for example red) for all the pixels and divide the total by the number of pixels. Both are easy tasks and therefore ideal challenges for a beginner to learn Processing. If it doesn't work out, then show the code of your attempt. Many people on this forum will be able to tell you what's wrong if it doesn't work.

bensen_ger

Re: Numeric values from a pixel image

1 year ago

Thanks for the advice. I will do just that.

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