What is a Bitmap (Raster) Image?
Why you’ll need your logo in a wide range of pixel-based formats.
There can be some confusion in the naming of pixel based formats – some designers refer to the entire family as bitmaps (there is actually a specific file format known as .BMP – the file extension is an abbreviation of bitmap) or raster images. Whenever a designer refers to a “bitmap” or “raster” image, they are talking about an image that’s made up of pixels. In the simplest terms, any pixel-based version of your logo will be a universal image format that you can use in a wide range of applications without requiring specialized software or applications. It is primarily an image for viewing, not editing. Raster images are vastly different than vector files in that they are not made up of vector shapes, but pixels arranged on a grid in various colors that when viewed together, make up the images you see on websites and social media.
Bitmap Files: Technical
Whereas most printed material uses tiny dots (known as screens) anything you view on an electronic device – desktop computers, smartphones or tablets – uses a grid to preview images. The individual squares of this grid are known as pixels, and the resolution of an image refers to the number of these pixels every inch, often abbreviated to .PPI. Many often refer to this resolution in printing terms too – .DPI or dots per inch – and the terms refer to the same thing when dealing with electronic images. Generally speaking, the resolution for electronic devices and screens is 72 DPI or PPI (there are some exceptions, like the new Retina devices from Apple that preview at a higher screen resolution.) There are several bitmap or raster image formats you’ll need to have your logo set up in and while each has specific properties of their own, they all look like this when magnified:The closer you get to a bitmap image, or if you increase the viewing size without also increasing the resolution of the image, the individual pixels become more and more visible. For this reason, you must always use any pixel based image format at 100% or less than its actual image size. Enlarging the image, particularly of your logo, above 100% will render the image “blurry” or “jagged.”
Bitmaps and Printing Resolutions
Because they are created using tightly packed pixels, bitmap images must be in the resolution of the output device that they’re being used on. On a monitor that equates to 72 PPI. Desktop printer resolutions vary, but they are often in the 150 DPI range. Office supply stores that print documents digitally can range from 150 DPI and up. In offset (professional or commercial) printing resolution requirements increases to a minimum of 266 DPI (higher for glossy paper stock.)
Bitmaps and Color Spaces
Bitmap images can have one of two color spaces. RGB (Red, Green, Blue) – these are images that are used in electronic devices and use their native color system. The second is CMYK (Cyan, Magenta, Yellow, Black) – these are images that are set up for use in traditional printing. Most desktop printers will convert RGB images to CMYK when printing.
Caution: Using a bitmap image in the incorrect color space can cause colors to shift. Certain RGB colors cannot be reproduced in the CMYK environment.
Pixel-based bitmap or raster formats can generally be identified by the following file extensions –
.JPG (Joint Photographic Experts Group.) An image format that has various “compression” levels to reduce file size. Used primarily for photographs or logos with complex blends and gradients.
.PNG (Portable Network Graphics.) Created to be a lossless alternative to the .GIF format, this is currently the most widely used format on the Internet today and is as close to a universal standard as we’re probably going to get. Details.
.BMP (Bitmap.) Bitmaps are lossless, high quality image files. As they do not feature file compression, tend to have much larger file sizes than .JPGs or .PNGs. As these are a favored Microsoft format, they tend to work very well in the Windows desktop environment and in software like Word.
.PS (Photoshop.) While technically pixel based, not considered a viewing image, but a proprietary working file for Adobe Photoshop software. May contain layers, masks, typography and other additions to the artwork. Files in Photoshop are not used “as is” but “saved as” into the various formats above. Generally requires Photoshop to edit, but as this application is considered standard in the graphic design trade, can be opened by several graphics packages (though not all the Photoshop features may be supported.)
Pros of Pixel Based Raster Files:
✓ Images can contain rich detail and complex tones (photographs.)
✓ Device & software independent. Can be viewed on all electronic devices.
✓ Can be used on all websites and Internet platforms.
✓ Can be small file sizes (when used at small image sizes or compressed when saving.)
✓ Can be added to most office software programs easily and with little technical know-how.
✓ Used in email as inserts or signatures.
Cons of Vector Files:
✘ Must be used at 100% image size or less. Enlarging a bitmap image will cause it to look jaggy or pixelated as the individual pixels become visible.
✘ Cannot be easily edited.
✘ Larger image files can mean larger file sizes. On a website this translates to slower download time.
✘ Details can be difficult to ascertain at very small sizes. In terms of logos, words can difficult to read or complex details hard to make out.
The resolution of any bitmap image depends entirely on where it’s being used. If your logo is headed for a website, social media or the Internet, it should be at 72 PPI. If you’re printing your logo on paper or goods, that resolution can vary from 150 PPI to 300 PPI and higher. The higher the resolution, the larger the file size.
Bitmap File Uses:
Under certain circumstances bitmap files of your logo can be used to print anything, but in general terms, the primary use of these files will be on websites and the Internet. Can be imported into most office software applications.
Not Appropriate For:
✘ Bitmap files are generally not used to edit your logo.
✘ Large size reproduction. Bitmap images of your logo, if used at very large sizes, can be extremely large & impractical file sizes.
✘ While they can be used in offset printing, it is not recommended that you supply your printer – unless they specifically request it – a bitmap version of your logo. It is always advisable to use a vector based version if you can.
Bitmap (Raster) Files – Frequently Asked Questions
I need my logo to have a transparent background for my website.
In practical terms, the only bitmap image format that can feature a transparent background is a .PNG
Exceptions: .GIF images can have a transparent background too, but this format is lossy – degrades the original image – and the PNG format produces a much higher quality image, usually without appreciable file size increase. Other than .GIF animations, this format has been largely rendered obsolete.
Other bitmap image formats either can’t be transparent – .JPGs require a solid background – or aren’t suitable for internet or website usage – .BMPs for example.
To make my logo bigger, can I increase the image size in my software?
No. Increasing any pixel based bitmap or raster image larger than 100% of its original image size will make it appear “burry” or “jagged” as the pixels become more apparent. This effect becomes more noticeable the larger you increase the image. Office software like Word does not add pixels, or change the resolution of the image when you make it bigger. You’ll need to use a larger image, or one with higher resolution.
I only have a small JPG of my logo. How can I make it bigger?
As the resolution of a bitmap image is fixed, you cannot increase the image size without severe quality degradation. In order to increase the image size, you’ll need to have one created from scratch, using a vector file as a “source” to save a pristine image at a larger 100% size. If you don’t have access to a vector version of your logo, you’re going to need to get one made. A vector version of your logo is a necessity for any professional brand identity management.
Can I edit my logo if I only have a JPG version?
There are some exceptions – but those require a great deal of technical know-how and access to professional level design software – but generally speaking, no, it is not possible to edit your logo if you only have access to a .JPG or other bitmap format. You’ll need to have access to a vector version of your logo but even that will require some technical experience and access to Adobe Illustrator or similar. Generally speaking, bitmap files are “end results” and created from vector source files.
Which files do I use for Microsoft Word or other software?
Most modern office software like Microsoft Word can handle all bitmap image formats (with the exception on Photoshop files.) Results will vary depending on the color space the original image was saved in, the type of format, the size and resolution. Some versions of office software have difficulty dealing with .PNGs with transparent backgrounds (try assigning the image a white background or “turning off” the transparent background entirely.) The optimum format for Microsoft office software still seems to be .BMPs but .JPGs are perfectly acceptable.
Which files do I use for my website?
You can use either the .JPG or .PNG format for your website. In terms of a logo, the .PNG format is preferable as it can feature a transparent background – your logo can “sit” on any color background or even on a photograph. .JPGs are preferable if your logo contains a lot of blends or gradients as they can “band” in a .PNG format (but keep in mind, a .JPG image cannot feature a transparency.)