Bitmap

Think of a cross-stitch pattern or a paper-scrap mosaic you made as a kid. You fill each little square with a bit of paper or thread in its assigned color. Step back, and a landscape or a face appears.

Computers handle images the same way. The screen is divided into very tiny squares, and each square gets an exact color value, like a numbered ticket. The smallest square that holds color information is called a pixel.

The photos you take with your smartphone and the wallpapers you download (JPG, PNG) are all made this way. Millions of dots come together to create natural light, shadow, and color, so bitmaps are the best choice for realistic photos.

At its original size, a bitmap looks smooth and clean. But zoom in on tiny text or a person's eye, and the edges turn jagged like stairs. Blocky squares show up.

People often say the photo got "pixelated." This happens because the fixed-size pixels get bigger along with the image. A bitmap only has the number of dots it was created with, so no matter how far you stretch it, it can't create new detail that was never there.

Vector graphics work differently. They draw lines and shapes using math formulas, so they stay sharp at any size. The trade-off is that vectors can't capture subtle, rich color changes as naturally as a bitmap can in a photo.

What decides a bitmap's quality is how many dots fit in its grid, across and down. The number of pixels in width and height is called resolution. It's usually written as 1920×1080 (Full HD) or 3840×2160 (4K).

At the same display size, higher resolution means the picture is drawn with more, smaller dots, so it looks much sharper and clearer. But each dot has to store brightness values for red, green, and blue (RGB). Without compression, the more dots you have, the more data the computer has to store, growing in direct proportion.

That's why high-quality bitmap files can get very large. To solve this, image compression technologies have developed alongside bitmaps. Lossless compression (like PNG) restores the original exactly. Lossy compression (like JPG) trims color differences your eyes can barely notice to shrink the file a lot.