DPI (Digital Photography Ignorance of Size)
In general, the long standing rule has been 300 DPI for printing. The term DPI stands for Dots Per Inch. This is the resolution of the image when printing on paper. Please note that DPI has absolutely zero importance in the image while you are editing it. Typically images will come into your editing software at whatever the default might be set to, such as 300 DPI, 240 DPI or sometimes even 72DPI. At this point in playing with the images, you do not care.
It’s important to understand that the computer considers a photograph merely to be a collection of dots of different colour and brightness, but they do not have any dimensions set to them. It is not until the image is being printed, or scanned, that the actual real world dimensions come into play. So for editing, don’t worry about DPI.
In the screen grabs below you can see a couple examples of a Photoshop Image Size pop-up window showing data for the same image with different DPI values. You will note where it says Resolution it changes from 300 to 72. Also note that there is a corresponding increase in the Width and Height of the image in inches. What does NOT change is the Pixel Dimensions between the two versions of the same image. Thus, there is NO difference between these two images in the computer. The ONLY difference occurs when printing and it will try to use the Document Size values as the size on paper. The screen does not change. The stored file on the compute does not change.
So, if you decide that you want an image printed at 16×20, adjust the size in one of the two Document Size windows (either width or height) and allow the resolution value to change as it wants. In another general rule, as long as the final Resolution value is over 200 pixels/inch, you should be safe. This is especially true for very large prints.
Why would that be more true for large prints than small prints? Well, first let me qualify the term ‘large’ as being an image with the smallest dimension over 16 inches. The reason that this matters is that when you have a large image, the viewer will not be holding it in their hand like a photo album or 4×6 print and noticing the resolution (or lack of it). They will be standing back some distance to take in the whole image comfortably. That added distance tends to reduce the acuity of the viewers vision slightly and make it less critical to lower resolution images.
Personally I have printed some images as low as 140 DPI with very acceptable results, but this is highly image dependent and best suits images with a lot of random detail and no regular lines or curves, such as a forest or irregular landscape images.
There are lots of online references around, but the most succinct that I found is located here: the-myth-of-dpi
What Not To Do
On the above screen shots there is a small checkbox near the bottom of the image with the title Resample Image. Notice that it is NOT checked. Do not check this box! This should only be used when you want to throw away the detail in your image to shrink it down for emailing, or web distribution at a smaller file size.
For images destined for printing, do NOT check this box. You want all the resolution you can get!
Most cameras store the images in .jpg format. This is the most common format and if used wisely is fine for general image work and printing. One of the issues that can creep into the use of .jpg (aka jpegs) images is the repeated opening, editing and saving causes the image to degrade slightly each time due to the image compression algorithm used. My recommendation is to make sure you are saving at maximum quality at all times. If you want to push something up to Flickr or social media websites, generate a special reduced size (now you can check the Resample box), and save at a quality of 7 or less. This will significantly reduce the file size and make those looking at your image see a faster response as they flip through them. Just remember, that should be a separate file saved somewhere else on your computer with some change to the filename to show it’s a special version.
Now, there are other file formats that are exceptionally useful in the workflow toward printing.
RAW format is generated by most DSLR and the newer mirrorless cameras and even a few point-n-shoot’s. This is a file that is simply just the data that the sensor captured, along with the camera setting information. Usually when I look at RAW images from the camera they don’t look so attractive. The reason for that is that when a camera shoots in .jpg format (typical default) it has some internal software that evaluates the sensor data and tweaks it into a standardized pretty image based on broad demographic definitions of what is considered pretty. That’s why I almost never shoot in .jpg. I want control!
When you open a RAW file you will need to use a RAW converter program, such as are built into Photoshop (Camera RAW) or Lightroom. This extra step injects a whole pile of control in the initial image you work with, but discussion of that is way beyond the scope of this article.
TIFF (tagged image file format) is also popular and has the added benefit that it will allow you to store image adjustment layers in Photoshop as separate layers that you can go back and change/delete later. The .jpg format permanently merges the adjustment layers into a single layer and saves this as the image. TIFF does not have this limitation and it also has a ‘zero compression’ option that will not affect the image quality when you save. For this reason, much of my serious editing is done with TIFF images.
PSD is a proprietary Photoshop format that is similar to TIFF, but less generally useful outside of Photoshop or the Adobe Creative Suite of programs. I use this too, but mainly because….well…..because. I like TIFF and PSD about the same. PSD format is the only format that supports every Photoshop feature, but TIFF supports so many of them that I’ve never observed a difference. PSD is for workflow, TIFF is more generalized, perhaps to just lay it out simply. If you send me a PSD file to print from, I’m good. If you send it to Astro-Mega-Print-House and Coffee Emporium, probably less so.
Seen from the Bund district, a common sight in this port city.
So your printing guy has a 24”, 36” or (wow) a 44” wide printer. Cool, eh? Imagine your image 44 inches high by whatever (maybe 72”?) wide. That would be so cool….until you try to mount it, frame it, plaque it, or any method known to humankind other than dodgy thumbtacks in the top two corners into the drywall.
Alright, maybe that’s not so much fun.
So, how large should you print your photograph?
I would wager a bet that the vast majority of privately produced photography is printed somewhere between 16”x20” and 20”x30”. Why? Well, traditional framing will add 3 to 4 inches around each side for width. Thus a 20”x30” image gets about a 28”x38” frame. That’s pretty large for most walls in typical homes. An 11×14 image would often get put into an 16”x20” frame, very comfortable for having two or three images on a wall that goes the full width of a room, or two on a stairway, etc.
Its worth measuring your space and imaging it with art work on it. Also, remember the old saw that “less is more”, meaning having four pieces jammed into a space where the frames are nearly touching would not look anywhere near a nice as three images with half an image width gap between.
The other reason for printing modest (but not tiny) sizes is cost. Even using the most premium of printing media generally would only cost you 1/4 to 1/3rd of the final framed cost when using most retail framing outlets (but I can help you with some lower cost recommendations, too). It is not at all difficult to find out that you’ve put all your money into the print and not allowed enough for the framing. Also, most framing materials come with a standard long dimension of 40 inches. If the final frame is over 40”, you might well find you are into premium price territory.
There are other options mounting, many of which can handle much larger sizes, such as plaque mounting (not archival), or on Gatorboard (a high quality foam core), or even aluminum (I’m dying to try printing on this, but its very expensive, also).
My summary recommendation is printing slightly smaller than you imagine you need, rather than larger.
For more information on my printing services here in Burlington, Ontario, please visit Fine Art Digital Printing
As a final comment: While I truly respect that folks like to get 4×6, 5×7 and 8×10 prints done, from a cost point of view you are much better off going to a local grocery store or photo shop. The print quality is not all that noticeable in the smaller sizes and my primary focus (pardon the pun) is to give the highest quality images to those prints that will really show off the efforts and skills of a Fine Art Photographer. In short, I can’t (and wont try to) compete with them.