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Resolution vs. Size
Optimizing bitmap images for large format digital production
How "big", or what "resolution" should your original artwork be, for it to look good at the final size? The answer to this common question depends on many factors, so let's first break it down by the two most common types of artwork: vector and bitmap.
1. VECTOR ARTWORK — The easiest way to define vector artwork, although not the most technically accurate, is that if the final files submitted for production originate from one of the popular vector graphics programs such as Adobe Illustrator, Corel Draw, or Macromedia Freehand, then it is considered "vector" artwork. Files from these applications are normally composed of lines, curves, text, geometric objects and/or PostScript fills, which can ideally be scaled to any proportional size without distortion or pixelation. When submitting these types of files for Large Format production, skim over this brief checklist to optimize the scaling to final size:
- Build and submit vector artwork at a whole-integer fractional size of the final, that's convenient for you to work with. You may want to use a size that fits on your own in-house printer. Or, if you prefer, it's also okay to build the artwork at final size, as long as your particular software is capable.
- Make sure your dimensions are proportional to the final size requested.
- Set a rectangle (with thin black or red stroke, and no fill) around the entire artwork, to indicate cut line. This helps to cleanly sidestep the often-unstable approach of using "page size" settings in your software to indicate cut line. When we enlarge your artwork to final size, this cut line should match your final requested size.
- If there are any thick lines or strokes in the artwork, preferably convert them to fills, to prevent problems with scaling accuracy, and even possible PostScript or RIP errors during production.
- If there are any bitmap objects such as photos, logos or textures that have been imported into this artwork, please also follow the "Bitmap" instructions below.
2. BITMAP ARTWORK — Any digital file whose original source is a scanner, digital camera, or bitmap graphics program such as Adobe Photoshop, is considered bitmap artwork. Perhaps the most common challenge encountered with customer artwork is when bitmaps are submitted at a lower resolution than necessary to yield the "visual quality" expected by the customer, at final size. To protect against this possibility, first review the following factors that impact visual quality:
- final size - What are the desired dimensions of the final print?
- viewing distance - From how far will most people be viewing the final image?
- print media - On what type of paper or material is the image being printed?
- source - How was the artwork first captured?
- content - Is the subject a nature scene, or peoples' faces, or a product, or ?
- treatment - Has the image been intentionally blurred or faded?
Now, skim through this short list of general "rules" to help arrive at a kind of baseline recommended image resolution, at final size:
- Trade show, retail and showroom viewing is 100 dpi optimal, 50 dpi minimal.
- Fine art and handhelds are 200 dpi optimal, 100 dpi minimal.
- Roadside displays are 75 dpi optimal, 20 dpi minimal.
- Textured media, such as polycarbonate and canvas, lower the minimum resolution.
- Subjects such as nature scenes, textures and abstract artwork are more visually acceptable at lower resolutions.
- Subjects such as human faces, logos, and photos of small products like hardware and appliances are less visually acceptable at lower resolutions.
- Blurring - When an image is intentionally blurred for effect, the "minimum resolution" is lower.
- Fading or ghosting - When an image is made mostly transparent, or lightened, the "minimum resolution" is lower.
- Pattern modeling - Some images can be resolution-enhanced with Blue River's premium Pattern Modeling process, where a trained technician uses specialized software and complex mathematical algorithms to read and duplicate pattern detail. This is not similar to upsampling (as in Photoshop's "Image Size"), a rudimentary method for adding pixels to an image without adding detail. A whimsical but descriptive analogy to our Pattern Modeling would be to "enlarge" somebody's front lawn by adding similarly shaped and textured blades of grass between each existing blade, rather than enlarge the existing blades. While improvement is noticeable with almost any image that is processed in a range of 200% to 600% scaling, some types of content such as human faces, textures and natural scenes yield better results than others, such as hard-edged product photos, logos and architectural images.
Lastly, don't confuse image resolution with printer resolution — optimal image resolution is intentionally lower than printer resolution, so that the printer has "extra dots" to build and transition colors, shades and edges. Exceeding the stated optimal resolutions will not increase visual quality, but may increase consumption of production resources significantly. For example, if you double your image resolution, this will multiply both your file size, and the necessary production time, by a factor of 4.
3. VECTOR/BITMAP BLENDED ARTWORK — Most of the above-named graphics programs, as well as other popular titles such as Adobe PageMaker and Quark Xpress, now have the capability to generate both vector and bitmap artwork within the same file. For example, a poster created in Illustrator or Photoshop may contain both a photo in bitmap format, and text in vector format. For these types of artwork, simply keep in mind the considerations from both categories above, with the following reminder: If your bitmap images are smaller than the total final size of the finished display piece or banner, the bitmap size and scaling issues apply at the final size of just the bitmap itself, rather than the final size of the entire piece. For example, a 12-inch square photo in one corner of an 8-foot banner only needs to have enough resolution to perform at 12 inches, not at the size of the total banner. |
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