Bitmap Images

What Are Bitmap Images? A Designer’s Guide to Image File Formats

Bitmap raster imagery

MAIN TAKEAWAYS:

  • Bitmap images consist of tiny squares called pixels that hold specific color information.
  • Common file formats for bitmap images include JPEGs, PNGs, GIFs, and TIFFs.
  • The ideal resolution for bitmap images depends on whether a design file uses variable data.
Bitmap images play a fundamental role in harnessing the power of digital inkjet technology to create vibrant, vivid images and colors. In-depth knowledge of bitmap images is also key to ensuring a smooth, error-free printing process.

“Each type of inkjet press has different image resolution, quality, and size requirements — all of which affect overall file preparation,” write Elizabeth Gooding and Mary Schilling, authors of The Designer’s Guide to Inkjet, 3rd Edition. “It’s especially important to design and save files according to the specifications of the inkjet press and the workflow of your specific print partner.”

With this in mind, here are some things we think graphic designers should know about bitmap images to produce the kind of world-class print materials associated with digital inkjet. 

What are bitmap images and why are they important?

Short for binary digital map, a bitmap image consists of a grid of tiny squares called pixels. Each pixel holds specific color information, which collectively represents every detail in a design file, including texture and color gradients. Bitmap images differ from vector images in that they do not rely on mathematical formulas to define shapes.

Bitmap images are crucial because of how inkjet presses apply ink to a substrate. Inkjet printers drop ink in tiny droplets on a pixel-by-pixel basis, and the printer’s ability to apply ink accurately depends directly on the bitmap’s pixel data. Errors in bitmap data translate to poor color quality and subpar image reproduction.

As the building blocks for high-quality inkjet prints, bitmap images help designers and printers accurately reproduce vibrant, nuanced colors and detailed design elements. Without a strong understanding of how to use and optimize bitmap images, designers cannot fully leverage digital inkjet print technology.

Bitmap imagery

What are common file formats for bitmap images?

Bitmap images come in several common file formats, each one with a specific set of characteristics or uses. Understanding these formats and their attributes makes it easier to choose the right file format for your print needs. Common file formats include:  

  • JPEG, which is used for photographs due to the file’s compression capabilities
  • PNG, which is ideal for images that require transparency
  • TIFF, which offers lossless compression for printing high-quality images
The good news is converting bitmap images to your required file format is an easy process that can be completed quickly via any number of graphic design platforms. 

What’s the ideal resolution for bitmap images?

The ideal resolution for bitmap images depends on a couple of factors, most notably where a file uses any variable data. While the standard resolution for digital inkjet is 300 dpi, the introduction of variable components changes best practices for achieving the highest resolution. 

“If the job has variable content with many variable images and significant data requirements, your service provider may require images to be provided in 300 dpi or lower,” explain Gooding and Schilling. “For some device and media combinations, file sizes above 300 dpi may not deliver different visual results anyway.”

 In other cases, print providers may require detailed images and barcodes to be delivered at 600 dpi. This is often the case if a job is fixed or has very few variable images and doesn’t have large data requirements. 

The recipe for high-quality digital inkjet print — or any type of print for that matter — hinges on a collaborative partnership with a print provider. This is why establishing a clear line of communication with a printer at the beginning of a project is key in optimizing the final product. 
Color spaces

What color space should be used for saving bitmap images?

Not all printers require bitmap images to be saved in CMYK color space. Some service providers prefer images saved as CMYK rather than RGB, while others can accurately convert RGB files to CMYK during printing.

This variation exists because each inkjet device’s workflow handles rasterization differently through RIP software. It’s essential to confirm the preferred color space with your printer to prepare your Adobe® Photoshop files accordingly.

“If you are matching CMYK color space images to a specific target output destination color space (GRACoL/CRPC or SWOP) for the purpose of matching across inkjet and other devices, talk to your print provider to ensure they will maintain the target color space for your images,” advise Gooding and Schilling. 

Some printers may ask you to save your images with the ICC profile of the destination color space in Adobe® Photoshop and may want the final PDF tagged with the destination color space and rendering intent information.

Bitmap imagery

The Designer’s Guide to Inkjet, 3rd Edition, has everything you need to know to create press-ready files for digital inkjet print.For graphic designers who are ready to print, the PrintAccess® directory of printers can help you find the right digital inkjet printer for your project. 

Download the guide or access the directory to connect with your ideal print partner.