Creating wide-format print designs with Photoshop® can wield some hefty files. Determining an ideal resolution or pixels-per-inch (ppi) for your design can help. Understanding when and why to design with Photoshop can help even more.
Photoshop is a resolution-dependent bitmap editor, which can create vector objects that are not resolution dependent (the objects become pixels as soon as you flatten the Photoshop document layers).
Wide-format designs with text and flat-color graphic shapes are created most optimally in Adobe Illustrator®. Vector objects are not resolution dependent, so their size comprises much fewer megabytes. You can scale Illustrator’s vector art infinitely, which allows you to confidently design at a scale factor because no image-quality degradation will occur when you scale the image for output.
If your wide-format designs require Photoshop, below are some helpful tips. Know, however, that Photoshop is required for photographs. It handles textures, shadows and glow effects better than Illustrator does, because these items are rasterized at output. Often, the best workflow utilizes the strengths of both Photoshop and Illustrator.
Understand ppi
Pixels-per-inch (PPI) is often confused with dots-per-inch (DPI), so think of ppi as the digital image and dpi as the output device.
The ppi figure is a measurement of pixels per printed linear inch. A printed, 100-ppi image — one that measures 100 x 100 pixels — will cover 1 sq. in. More importantly, the ppi figure will determine the resolution of your printed Photoshop image.
Determine the ideal ppi
Consider several factors when deciding on the best ppi for your Photoshop design — type of design, output device, print size, media and viewing distance. Most importantly, don’t create more pixels than necessary, because, at a certain point, there’s no return on your pixel investment. The ideal resolution is probably smaller than you think.
Testing is a best way to determine the ideal ppi. Create a test-print document that represents your typical design and set its dimensions to the final print size. Start with your highest, typical resolution (label the resolution somewhere in the image). Lower the resolution in 50-ppi increments and save a new, labeled file each time. To change the image resolution, go to Image > Image Size. Check all three boxes: Scale Effects, Constrain Proportions and Resample Image.
Print a sample set of these files on each output device and media type. View the printed samples at various distances. Consider the average viewer’s reading distance. For example, a billboard’s resolution may be as low as 10 ppi.
Once the ideal resolution is determined for each factor, you’ve established a dpi-knowledge base, which allows you to start each new Photoshop design at the exact print dimension and correct ppi.
Design in RGB
An RGB document comprises fewer megabytes than a CMYK file with the same pixel count, because a CMYK file has one more color channel than an RGB file.
If your printer requires a CMYK file, perform the RGB/CMYK conversion last. Design in RGB and, when done, flatten the final design and convert it to CMYK.
Photoshop vector shapes
Design with vector-shape layers instead of pixel layers. Apply pattern effects to vector shapes for textured backgrounds. A vector shape with a pattern effect is much smaller than an image layer.
Avoid Smart Object layers
Bitmap, Smart Object layers rapidly increase a Photoshop file’s megabyte size. For example, placed images from Mini Bridge always default to Smart Objects. Rasterize Smart Objects by going to Layer > Rasterize > Smart Object. Smart Object layers are identified by a page icon in the layers palette. Double clicking on a Smart Object layer will open the smart object in its own Photoshop document.
Alpha Channels
Saved selections become Alpha Channels, viewable in the Channels palette. Alpha Channels are grayscale bitmap information, and they add megabytes to the document size. Delete extra Alpha Channels by dragging them to the trashcan icon at the bottom of the Channels palette.
Crop extraneous pixels
Pixels that fall outside of the document boundaries are hidden from view, but they add megabytes to the document size. This happens frequently with placed images that are larger than the layout. Delete these pixels with the Marquee tool. Select the entire document (Command or Control A), then go to Edit > Crop.
Clean up layers
Delete unused or hidden layers. Merge layers that create a look that makes you happy.
File saving options for print
These saving options use consume less file space:
TIFF — Flatten the document layers and save as TIFF. Don’t include layers or alpha channels. Save with LZW compression (it focuses on the design’s flat-color areas and can reduce the megabytes without sacrificing print quality). This method converts all text and vector objects to bitmap.
Photoshop PDF — These directions are for Photoshop CS6. A Photoshop PDF file may include all layers, text and vector objects from a Photoshop design if it’s saved correctly.
Save as Photoshop PDF — with Layers selected and the ICC profile embedded.
Say okay to the warning message about the PDF dialog possibly overriding your current settings. The following steps will ensure the layers are intact.
Choose the Adobe PDF Preset (Press Quality) — Leave all the General default options as is. Set all Compression options to None. Set the Output Color options to No Color Conversion and Include Destination Profile. Essentially, the resulting PDF is a Photoshop file wrapped up as a PDF. The file contains transparent information and, to print it, you’ll need a RIP equipped with the Adobe® PDF Print Engine.
Final advice: To ensure each person’s work comes together properly, talk with the printshop’s pre-press person and print-machine operator, to learn his or her exact requirements, before starting your design work.