Frequently asked questions


Working with images can be confusing. Bear these key facts in mind and it could help to eliminate much of the hassle.




Raster v Vector

 

If you’re confused over the difference between the many image file types, you’re not alone. When starting off a project, one of the first things we request from our client is a vector file of their logo. However, that request is often met with blank stares or responses like “Can’t you just pull the logo from my site?” As a marketer, understanding the importance and role of different image file types. It is essential to ensuring your brand is properly represented and to better communicate with designers, developers and printers.

Let’s start making sense of the issue by clarifying the difference between the two major image types – raster and vector.


rasterRaster

 

Raster images use many coloured pixels or individual building blocks to form a complete image. JPEGs, GIFs and PNGs are common raster image types. Almost all of the photos found on the web and in print catalogues are raster images.

Because raster images are constructed using a fixed number of coloured pixels, they can’t be dramatically resized without compromising their resolution. When stretched to fit a space they weren’t designed to fill, their pixels become visibly grainy and the image distorts. This is why altered photos may appear pixilated or low resolution. Therefore, it is important that you save raster files at precisely the dimensions needed to eliminate possible complications.


vectorVector images, alternatively, allow for more flexibility.

 

Constructed using mathematical formulas rather than individual coloured blocks, vector file types such as .EPS, .AI and .PDF* are excellent for creating graphics that frequently require resizing. Your company logo and brand graphics should be created as a vector and saved as a master file. This is so you can use it with smaller items such as your business card and letterhead, but also on larger surfaces, such as vehicle livery or your shop front. When necessary, always create a JPG or PNG for use on the web from this master vector file.

Just be sure to save the new raster file in the exact dimensions needed.

*A PDF is generally a vector file. However, depending how a PDF is originally created, it can be either a vector or a raster file.

Whether you opt to flatten the layers of your file or choose to retain each one will determine the image type.



To determine whether your raster images are a suitable resolution for a specific application, you need to check their pixel density.

DPI or PPI

 

Units of measurement such as dots per inch (DPI) or pixels per inch (PPI) refer to the number of pixels in one inch of the image. These measurements become important when you attempt to use raster images in specific places, such as on the web or in print publications. The web, for instance, displays 72dpi (72 dots or pixels per inch) – a relatively low pixel density. Raster images with a low DPI like 72dpi look nice and crisp on the web. But this same low DPI image may not be suitable for printing on a brochure or packaging. To correctly print an image, it should be at least 300dpi, a much higher pixel density than the web displays.

Resizing a low DPI image pulled from the web to fit the dimensions of your print project won’t work because the same finite number of pixels only get bigger and begin to distort. For example, let’s say you want to print your logo at 50mm x 75mm on a brochure. If you have a 72dpi jpg of your logo and it’s 50mm x 75mm, it will need to be “stretched” to more than 3 times the size to get it up to 300dpi. That 72dpi logo may look great on your computer monitor, but when it prints at 300dpi it will look pixilated. Instead you should use a vector version of your logo (.EPS or .AI) or create a raster (JPG) with the exact dimensions desired and at 300dpi.




JPG

 

JPG (or .JPEG) is a raster image that is often used for photographs on the web. .JPGs can be optimized, when saving them out of Photoshop, to find the perfect balance of small file size and high quality. On the web, you want your images to be as small as they can be so your site loads quickly, but large enough to still appear crisp and not pixilated. A JPG can’t have a transparent background so they are always in the shape of a rectangle or square with a solid background.

Best use = rectangle or square photos and photographs on your website.


PNG

 

PNG is another raster image type. For the general marketer, the main difference to understand between a .PNG and .JPG is that a .PNG can have a transparent background and is generally larger and higher quality. Therefore a .PNG is ideal for saving logo files for websites because they can be placed over a coloured background.

Best use = Logos, icons and other images where a transparent background is preferred.


GIF

 

GIF is another raster image type. A GIF is formed from up to 256 colors from the RBG colorspace. The fewer colours and shades contained in an image, the smaller the file size. Therefore a GIF is ideal for images that use just a few solid colors and don’t have gradients or natural shades. In other words you wouldn’t want to use a GIF for a photograph.

Best use = simple web graphics such as web buttons, charts and icons.


TIF

 

TIF(or TIFF) is a large raster file. It has no loss in quality and therefore is primarily used for images used in printing. On the web, because of load time, you generally want to use smaller images such as JPG or PNG.

Best use = Images and photographs for high quality print.


EPS

 

EPS file is a vector file of a graphic, text or illustration. Because it is vector is can easily be resized to any size it needs to be. An EPS file can be reopened and edited.

Best use = Master logo files and graphics and print designs.


AI

 

AI file is a proprietary, vector file type created by Adobe that can only be created or edited with Adobe Illustrator. It is most commonly used for creating logos, illustrations and print layouts.

Best use = creating logos, graphics, illustrations.




Vector files such as AI and EPS can remain editable so you can open them back up in Illustrator and edit any text or other elements within the graphic. With images that contain which that are saved as a JPG, PNG or GIF, you would not be able to reopen and edit that text. At One Vision Signs we often create files in Illustrator and save an AI file as our master file, but then also save an EPS version, “in outlines” which is used in production and sent to print.

Saving in “outlines” is a term that you will hear when sending files to print. If a we don’t have a font you used in your design and the vector file is not saved in outlines then when we open the file the text won’t have the desired look as it will default to a different font. Saving something with “outlines” basically means you are locking the text so that it’s no longer technically a font but instead made up of vector shapes that form your letters. This is important when sending graphics to print.

Saving a file in outlines makes your text no longer editable which is why at One Vision Signs we keep the AI file as an editable master and then save an PDF as the locked final artwork which we send to print.



What is bleed?

 

When any image, element or background colour on a page touches the edge of the page then you will need to apply bleed to it. When you extend colour or image beyond the edge, leaving no margin it is said to bleed. It may bleed or extend off one or more sides. Photos, patterns and solid colours can bleed off the page. You will need to add bleed to each side that your artwork touches.

For instance if you have a solid colour background on your artwork you will need bleed on all four sides, or if you have an image touching just one side you need to bleed it off just that one side.

How to apply bleed

 

Bleed is artwork that is extended beyond the actual dimensions of the document. It is used to avoid strips of white paper showing on the edges of your print when cut to size. If a document has no bleed and the trimming is out by 0.5mm then you will end up with a white strip. That is why we recommend adding bleed to all documents. For One Vision Signs, bleed of 5mm is required. Depending on what program you are using, you may be able to apply bleed as you are saving as a PDF, in other programs that do not have that option namely Word, Powerpoint and Photoshop you will need to set up the page size as slightly larger to allow for the bleed.

General rule of thumb

 

Programs with bleed settings: Drag your colour, image or pattern 5mm over the edge where the document ends, so it extends outside the page. Then when you export or save as a PDF choose 5mm bleed settings. Programs without bleed settings: 10mm bleed accounts for each of the four sides of the page, therefore you should add 10mm to the width and 10mm to the height of the document.

Crop marks

 

Crop marks are the little lines that sit around the edge of the document showing where the area of bleed ends and the proper document area begins. They work alongside bleed to tell the printer where the paper needs trimming. Crop marks are usually hairline or 0.25pt in thickness and are set in Registration Black. Crop marks are applied when you save as a PDF. Make sure to select “apply crop marks or trim marks” before saving.




Inspired by an idea but not sure how to make it come alive?
Let us help you create your vision…
Contact us at info@onevisionsigns.co.uk or call 01793 537 474