Pixels - It is made up of two words - 'Picture' + 'element'. It is the smallest physical point or addressable element in a display image. They are generally represented as the square or dot and can only have a solid color. In some circumstances, they are corresponding to their timing mechanisms and sweep rates and even transparent.
The first step to understanding how to print high-quality photos is to understand pixels per inch (PPI). The pixels on your digital camera or computer screen get converted into dots on the printed photo.
Pixel density or PPI (Pixels per Inch) is not the measurement, they are pieces of information (data). It is the measurement of the resolution of devices in computer display, image scanners or digital camera image. The number of pixels displayed per inch is referred to as resolution.
Calculate PPI: The basic equation is PPI = width(pixels)/ width of image (inches); PPI = height(pixels)/ height of image (inches). So, for example, if you want to print a 4-inch-by-6-inch image, and your pixel count is 800 x 1200, you need to divide 800 (the pixel height) by 4 (the photo height) and then divide 1200 (the pixel width) by 6 (the photo width). The PPI will be 200, providing you with good quality photos. However, if you want to print a larger photo, for example 8-inch-by-10-inch photo, the PPI reduces to 100 for width and 120 for height, giving you lower quality prints.
Have a look to the below image to understand pixels clearly,
Pixels in a image
Lets a image is 2 pixels by 2 pixels with a resolution of 2 pixels per inch. Then, the image would contain 4 pixels.
Memory Cost of Images
Large images consume large memory and make our computers struggle. Memory cost for an image is computed from the image size.
For a 6x4 inch image at 150 dpi, the image size is calculated as:
(6 inches × 150 dpi) × (4 inches × 150 dpi) = 900 × 600 pixels
900 × 600 pixels is 900 × 600 = 540,000 pixels.
The memory cost for this RGB color image is:
900 × 600 × 3 = 1.6 million bytes.
The last "× 3" is for 3 bytes of RGB color information per pixel for 24 bit color (3 RGB values per pixel, one 8-bit byte for each RGB value, which totals 24 bit color).
BITMAP:-
It is the type of memory storage for display images, means the map of bits. The term bitmap implies one bit per pixel, while pixmap is used for images with multiple bits per pixel.
The number of distinct colors that can be represented by a pixel depends on the number of bits per pixel (bpp). A 1 bpp image uses 1-bit for each pixel, so each pixel can be either on or off. Each additional bit doubles the number of colors available, so a 2 bpp image can have 4 colors, and a 3 bpp image can have 8 colors:
- 1 bpp, 21 = 2 colors (monochrome)
- 2 bpp, 22 = 4 colors
- 3 bpp, 23 = 8 colors
- 8 bpp, 28 = 256 colors
- 16 bpp, 216 = 65,536 colors ("Highcolor" )
- 24 bpp, 224 ? 16.8 million colors ("Truecolor")
For color depths of 15 or more bits per pixel, the depth is normally the sum of the bits allocated to each of the red, green, and blue components. Highcolor, usually meaning 16 bpp, normally has five bits for red and blue, and six bits for green, as the human eye is more sensitive to errors in green than in the other two primary colors. For applications involving transparency, the 16 bits may be divided into five bits each of red, green, and blue, with one bit left for transparency. A 24-bit depth allows 8 bits per component. On some systems, 32-bit depth is available: this means that each 24-bit pixel has an extra 8 bits to describe its Opacity (for purposes of combining with another image).
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