Raster (Bitmap) vs Vector

raster
vector
when to use which
vector & raster side-by-side pros and cons

RASTER VS VECTOR

Raster images are made of pixels. A pixel is a single point or the smallest single component in a display device. Let's think of them as little tiny squares* or dots of color or shade.

Vector images are mathematical calculations from one point to another that form geometrical shapes.

vector vs raster

I've magnified the raster and vector images above and we can easily see the differences between the two but sometimes you cannot see the difference at a glance on a normal view. Vector graphics also display an outline or wireframe view and this is very important for certain processes, more details below.

When a raster image is scaled up, it usually loses quality. A raster image can be enlarged by either adding more pixels (which Photoshop randomly - but smartly - adds) or enlarging the size of the pixel. Either way you are spreading the original data over a larger area at the risk of losing clarity.

A vector program will use a mathematical formula to build an image that can be scaled to any size without losing quality.

Raster Images

First let me say: Raster images are also called Bitmap images, pixels are also called dots, and dots-per-inch (dpi) sometimes called pixels-per-inch (ppi) although technically they have distinct meaning I may use those terms interchangeably in this website.

Raster images' dimensions are measured in pixels. Because raster images cannot be enlarged without losing quality, different suppliers have specific size requirements for their processes; they require a specific pixel resolution: a specific amount of pixels within each inch. The amount of pixels within each inch in the image represents the image pixel resolution or ppi (pixels per inch).

When we see an image on a 72 dpi monitor, we are seeing 72 pixels within each inch.

How large a raster image can be printed - and maintain quality - depends on 2 things:

    1. the pixel dimension of the image (e.g. 6824 pixels wide by 2345 pixels high)
    2. the pixel resolution: dots-per-inch (dpi) required by the specific printer

Some offset printers (paper printers) require a minimum of 300 dpi
Some screen printers (t-shirts, cloth) require a minimum of 240 dpi
Large format printers (banners, billboards) vary a lot because it also depends on the distance from which the sign is going to be viewed - could be as low as 20 or more than 200

How to determine what size your raster image must be, for good quality printing:

Multiply the resolution required by the area to be printed. Examples:

If a printer requires a minimum of 300 dpi and you want to print an image in an area that is 5 inches wide, multiply 300 pixels x 5 inches (300 x 5 = 1500). Your image must be at least 1500 pixels wide.

If a printer requires a minimum of 240 dpi and you want to print an image in an area that is 12 inches wide, multiply 240 pixels x 12 inches (240 x 12 = 2880). Your image must be at least 2880 pixels wide.

Can we enlarge the pixel dimension and resolution of a raster image?

Raster images have a certain amount of pixels within each inch. A 72 ppi image has 72 pixels in every inch. A 300 dpi image has 300 dots per inch. Usually the higher the dpi, the higher the quality. When you are required to provide a high resolution image file, the file must have been created or scanned at both the dimension and the resolution required. E.G. if you need to print an image at 2 inches wide and 300 dpi is required, your image must be created/scanned at a minimum of 600 pixels (2in x 300dpi).

Once the image is created at a certain dimension, you may not be able to use this image at a larger size without losing quality. The resolution and size can be manually increased but the quality may suffer. When you manually increase the resolution with a program like Photoshop, Photoshop randomly adds pixels and the result will most likely be a high resolution image of poor quality.

Sample of a raster image below:

Raster image made of pixels

How to determine what dimension your existing image can be printed at:

Divide the pixel dimension of your image by the resolution required by your printer.

To view and edit an image pixel dimension you must use a photo-editing program like Adobe Photoshop or Paint Shop Pro to open the raster file.

Examples:
If your image is 1993 pixels wide & printer requires 300 dpi (1993 ÷ 300) can be printed at 6.643 inches
If your image is 1993 pixels wide & printer requires 240 dpi (1993 ÷ 240) can be printed at 8.304 inches

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Common raster image files: jpg, jpeg, gif, png, tif, tiff, bmp, psd and pdfs originating from raster files
Common raster programs: paint programs like Photoshop & Paint Shop
Common raster images: photographs, paintings
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Vector Graphics

Vector graphics are made of mathematical calculations that form objects or lines - they do not use pixels therefore are resolution-independent which means they can be used at the highest resolution the output device allows:

Vector graphics can be enlarged and printed at ANY SIZE!

Instead of pixels, vector graphics use objects and lines (shapes) to represent images. Vector files can be scaled to any size without losing quality.

Some Vector programs have two different views; preview/normal view which displays the image as we normally would see it and an outline/wireframe view which displays the outline of every object in the file. This vector outline/wireframe is important to some companies like engraving & vinyl-cut signs because it guides the equipment they use to create their products.

For categorizing purposes I have named the above: photo-realistic vector, vector illustration, and vector lineart.

1. Photo-realistic vector: a photograph was traced as vector using a multitude of colors to allow the image to have a closer resemblance to original. This vector image can be used in many different processes like CMYK or digital printing, but as you can see from the outline/wireframe view, there are too many objects for it to work for engraving or vinyl-cut signs. Photographs are best printed as they are - raster images... Learn more.

2. Vector illustration. This is a hand-drawn, simplified illustration using a limited amount of colors and color blends. Color blends can be created in vector programs but they are actually raster effects so this image is NOT 100% vector. The raster effects show up as boxes on the outline/wireframe view. This vector image is suitable for many processes except those that are guided by the vector outline such as vinyl-cut signs or engraving.

There are other ways to achieve color blends,
please see traced vectorization of images with color blends

3. Vector lineart. This is 100% vector art; NO COLOR BLENDS. The outline/wireframe is acceptable for all processes including those that are guided by the vector outline.

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Common vector graphic file format: eps* ai, cdr, ps, pdfs originating from vector files
Common vector graphic programs: drawing programs such as Illustrator, CorelDraw, FreeHand
Common vector graphics: drawings, illustrations, cartoons

* eps and pdf files can originate from either raster or vector programs, and/or can include raster & vector elements. Is EPS Vector?

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If I am creating a new design which software should I use; Raster or Vector Graphic Program?

It depends on the design itself. If it's going to have photographic elements with continuous tones and blends of color, you are probably better off using a paint program like Photoshop which is a raster program that specializes in photo editing, or use any other PAINT program.

If you want your final design to look like an illustration instead with clear contrasts between objects & shapes, then use a vector program.

You MUST use a vector program when creating art for plotters, vinyl-cut signs, engraving and other specialty items.

Ideally a company that has a logo design with photographic elements, also has a secondary version of their logo in vector format that can be used for those specialty items that require vector art. Sample below:

raster and vector logo

Raster (Bitmap)

• Made of pixels; tiny dots or squares* of color

• Represents and edits photo and photo-like elements better than vector programs with the use of continuous tones. The use of different color pixels allows for smooth blends of colors.

Disadvantages

• Is bound by the number of pixels in the image. It cannot be scaled up without losing quality.

•Large (dimension) & detailed images equal large file size

• Some service providers like engravers, stencil-cut signs, etc, must have vector art.

• It is more difficult to print raster images using a limited amount of spot colors

• Depending on the complexity of the image, conversion to vector may be time consuming

Vector

• Made of mathematical calculations that form objects and lines

• Can be scaled to any size without losing quality

• Resolution-independent: Can be printed at any resolution

• Number of colors can be easily increased or reduced to adjust printing budget.

• A large dimension vector graphic can maintain a small file size.

• Vector art is required by many service providers

Can be easily converted to raster

Disadvantages


• It is not the best format for photographs or photo-like elements with blends of color

Is EPS Vector?
Vectorizing images with color blends
Vectorizing Photographs
Grayscale vs lineart

*A pixel is not a little square!
All "vector" images on this website have been rasterized, for browser compatibility, and display as bitmap images.