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Tool to read the color of a pixel in an image and extract the red, green, blue values or to extract all the pixels of the same color in an image.

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Tag(s) : Image Processing

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 The first pixel (top left) is indexed (x,y)= (0,0) (1,1)

## Pixel Extractor

 The first pixel (top left) is indexed (x,y)= (0,0) (1,1)

### What is a pixel? (Definition)

The pixel (from the contraction of picture element) is the smallest element defined by a color in an image.

The pixel is only defined in raster images, there is no equivalent for vector images.

### How to read a pixel in an image file?

The image must be in a readable format (JPG, PNG, GIF are the most common) and have a non-vector format in order to extract information on their width (number of columns) and height (number of lines).

The pixel reading is usually a number, it can be associated with a table of contents (if the colors are indexed) or with an N-bit value (usually 24 bits).

This number can then be translated into 3 components: Red, Green and Blue.

Example: The number 16711680 (which is written ff0000 in hexadecimal) corresponds to the color red, it has two components: 255 (FF) Red, 0 (00) Green and 0 00 Blue.

### How to extract pixels from an image?

Read each pixel, one by one, by row or by column and note the position of the pixels corresponding to a criterion.

To extract all the pixels having a given color, read all the values of each pixel and note their coordinates (rows, columns).

### How to read a transparent color?

Colors can integrate an alpha channel (called transparency channel), and although the color is totally invisible (transparent) it can contain a color.

### Why coordinates starts at row 0 and column 0?

In computer science, it is common to start counting the first element from 0. This practice greatly simplifies the calculations.

Most software will then note the first pixel (ie. reading the top left pixel) with coordinates (x = 0, y = 0).

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