Raster graphics are digital images made of a fixed grid of pixels, each storing a color value. In graphic design, raster images (also called bitmap images) are the natural format for photographs, painted textures and detailed tonal transitions, because each pixel can hold an independent color.
The defining limitation is resolution dependence: a raster image contains a set number of pixels, so enlarging it beyond that detail produces blur or visible pixels. This distinguishes raster graphics from vector graphics, which describe shapes mathematically and scale without loss.
How raster graphics store an image
A raster image is a two-dimensional array of pixels defined by its pixel dimensions, such as 3000 by 2000 pixels. Each pixel stores values for one or more color channels, for example red, green and blue, plus an optional alpha channel for transparency.
The amount of tonal detail depends on bit depth. An 8-bit-per-channel RGB image can represent about 16.7 million colors, which is sufficient for final delivery, while 16-bit-per-channel files preserve smooth gradients during heavy editing and reduce the risk of banding.
| Property | Typical values | What it determines |
|---|---|---|
| Pixel dimensions | From icons of 16 px to photos over 8000 px | Total detail available |
| Bit depth | 8 or 16 bits per channel, 32-bit float for HDR | Number of tonal steps |
| Color mode | RGB, CMYK, grayscale | Intended output medium |
| Color profile | sRGB, Display P3, Adobe RGB, print profiles | How values map to real colors |
| Alpha channel | Present or absent | Transparency and soft edges |
Resolution, size and output
Pixel dimensions alone determine how much detail an image holds. PPI (pixels per inch) only describes how densely those pixels are placed when the image is output, so changing PPI without resampling does not add or remove detail.
For print, the common guideline is about 300 PPI at final size for close viewing; large posters viewed from a distance can use 150 PPI or less. For screens, the relevant measure is pixel dimensions relative to the display, with 2x assets commonly prepared for high-density displays.
| Use | Resolution target | Reason |
|---|---|---|
| Magazine or brochure print | About 300 PPI at print size | Close viewing distance |
| Large-format poster | About 100 to 150 PPI | Viewed from several meters |
| Website hero image | About 2000 to 2600 px wide | Covers wide and high-density screens |
| App icon or UI asset | 1x, 2x and 3x sizes | Sharp on different pixel densities |
Upscaling a raster image must invent new pixels through interpolation or machine-learning-based enlargement. The result can look acceptable, but it cannot recover detail that was never captured.
Raster file formats
Raster formats differ in compression, transparency support and color depth. Choosing the right one balances quality, file size and compatibility.
| Format | Compression | Best use |
|---|---|---|
| JPEG | Lossy, no transparency | Photographs for web and sharing |
| PNG | Lossless, alpha transparency | Screenshots, interface assets, flat graphics |
| WebP | Lossy or lossless, transparency | Web images with smaller file sizes |
| AVIF | Efficient lossy or lossless, HDR support | Modern web delivery |
| TIFF | Uncompressed or lossless, layers possible | Print production and archiving |
| GIF | Lossless, 256 colors, animation | Simple animations and legacy uses |
Lossy compression discards information each time a file is saved again, so working files should be kept in a lossless format and exported to JPEG, WebP or AVIF only for delivery.
Raster graphics compared with vector graphics
Raster and vector graphics solve different problems, and most graphic design projects combine both. The comparison shows when each is the right choice.
| Aspect | Raster graphics | Vector graphics |
|---|---|---|
| Structure | Grid of pixels | Paths defined by points and curves |
| Scaling | Loses quality when enlarged | Scales to any size without loss |
| Best content | Photos, textures, painted detail | Logos, icons, type, diagrams |
| Editing | Pixel-level retouching, masking | Shape and node editing |
| File size driver | Pixel count and compression | Number and complexity of paths |
| Typical formats | JPEG, PNG, WebP, TIFF | SVG, PDF, EPS, AI |
A logo should therefore be created and stored as a vector and exported to raster only for specific outputs, whereas a product photograph is inherently raster and is isolated from its background with masking or a clipping path.
Common raster mistakes
- Enlarging small web images for print produces soft or pixelated results.
- Repeated JPEG saving accumulates compression artifacts around edges and in gradients.
- Missing color profiles cause colors to shift between applications and devices.
- Raster logos and text become blurry at large sizes and should be replaced by vector originals.
- Oversized images on websites slow page loading; images should be resized and compressed for their display size.
A non-technical view
A raster image is like a mosaic made of tiny colored tiles. From a normal distance, the tiles blend into a smooth picture, such as a photo of a face or a landscape.
The number of tiles is fixed. If the picture is stretched very large, the tiles become visible and the image looks blocky or blurry. That is why photos work well as raster images, while logos are usually made in a different way that can grow without limits.
A concrete example
A graphic designer prepares a trade fair banner that is 2 meters wide. The client supplies a product photo downloaded from its own website, measuring only 1200 by 800 pixels, and a logo saved as a small PNG.
At 2 meters wide, the photo would print at only about 15 PPI, which would look visibly soft even from a distance. The designer requests the original camera file of about 6000 by 4000 pixels, which yields roughly 75 PPI at banner size, adequate for viewing from several meters. The logo is replaced with the original vector file.
The printed banner shows a sharp product image and crisp logo edges, and the client avoids an expensive reprint caused by low-resolution raster artwork.