OPTIMIZING PRINTING RESOLUTION TO CREATE HIGH QUALITY PRINTS
One of the biggest joys of photography is creating beautiful prints of one's best images. Of course, we all want these prints to be of the highest quality. Why else would we spend all that money on the latest cameras, lenses, and editing software? In addition, many photographers have spent untold hours learning and fine tuning their image editing skills. Of course, we then print to a high quality printer in order to maximize the results.
Figure 1: Image Size
However, there is one step that affects the quality of the final print that some photographers miss -- optimizing the printing resolution. The printing resolution is the number of pixels per inch (PPI) at which the image will be printed. In Photoshop, this is set in the Image Size dialogue box (see Figure 1).
When setting the printing resolution, a problem is often encountered. Up to a point, higher printing resolutions tend to produce higher quality images. This is because the higher printing resolutions provide the printer with more information per inch than lower printing resolutions. On the other hand, the higher the printing resolution used, the smaller the print that can be made without interpolating the image to a larger size. For instance, in Figure 1, the printing resolution is 300 PPI. At this resolution, the image can create an 11.68"x 7.78" image. When a larger image is desired, there are two options available:
Make the print at a lower printing resolution.
Interpolate the image so that the image has a larger number of pixels.
While either of these options will allow a larger print to be made, they both tend to reduce image quality. Using a lower printing resolution sends less information per inch to the printer, and interpolating an image causes a degradation of the image detail by softening the edges (this issue is discussed in detail in my Interpolation article series).
So, there is a trade off. Using larger amounts of interpolation allows an image to be printed at a higher PPI (sending more information per inch to the printer), but the interpolation softens the image. Conversely, using smaller amounts of interpolation causes less softening of the image, but the image will be printed at a lower PPI (sending less information per inch to the printer).
However, this is not the end of the story. There are other factors that affect the optimal printing resolution for an image.
The printer is a factor. Some printers tend to print higher quality images a certain printing resolutions than at other resolutions.
The image may also have an affect on the optimal printing resolution. For instance, an image with a lot of fine detail may print better at one interpolation/resolution combination than an image that has very little fine detail.
RESOLVING THE DILEMMA
So, how can this dilemma be resolved? The answer is quite easy. For those times when the highest quality print is desired, test prints at several different printing resolutions should be made and compared. Then, the best print can be selected, and the printing resolution for that print used for the final print.
To carry out this process, a few points should be kept in mind:
Generally, the lowest printing resolution that should be considered is somewhere between 180 and 200 PPI. Below this printing resolution, image quality tends to suffer.
Earlier, it was stated that higher printing resolutions tend to produce higher quality images but only up to a point. Beyond a certain point, some printers simply throw away information. This will actually degrade the image quality. In general, it rarely makes sense to use a printing resolution beyond 360 PPI.
This provides a range of printing resolutions that should be considered. A photographer might print copies of the image at 200, 250, 300, and 360 PPI.
It is not necessary to print the entire image. A section of the image, that has good detail, can be used to produce smaller prints for the evaluation. This saves paper and ink. For instance, for a 20"x30" or 24"x36" print, I usually crop out a 6"x10" section that is used to produce the test prints.
This process should be carried out each time the highest quality print is desired. It can not just be done once, and the results applied to all images. This is because the results will change depending on a number of factors such as how much the image is enlarged, the interpolation method used, and the amount of fine image detail the image contains.
So, how does one create various prints at different printing resolutions? The procedure is easy. For each test print:
The original, uninterpolated image is duplicated.
The image is cropped to the area that is to be used for the test print.
The Image Size dialogue box (or other interpolation software) is launched.
The desired resolution is entered into the Resolution box in the dialogue box.
The final print size is entered into the document size box in the dialogue box.
The interpolation is started by clicking Okay on the dialogue box.
The image is printed.
EXAMINING THE IMAGE
Figure 2: Loupe
The differences between the prints may be subtle. So, the images need to be examined in good light. Furthermore, a loupe (see Figure 2) may be necessary to magnify the image in order to best see the differences in the image detail.
Now, the recommendation to use a loupe may elicit some negative comments by some photographers. They may argue that, if the differences can not be seen by the eye without the use of a loupe, the differences are insignificant, and the entire printing resolution issue is irrelevant. In other words, if the differences in the test prints can not be seen without the use of a loupe, any printing resolution will work just fine. Thus, carrying out the test print procedure is a waste of time and money.
I hear this same type of argument applied to a lot of different issues:
I can't see any difference between JPG and raw photos. So, why bother with raw?
My sharpening software seems to do just fine. Why bother creating customized sharpening?
Regular layers do the job. Why go to the trouble of using Smart Objects?
This viewpoint misses the big picture. The image data goes through quite a few changes from the point where it is captured by the camera to the point where it becomes the final image. Some of these changes occur in the camera. Some changes occur during the raw conversion. Often, many changes are carried out in Photoshop. However, one thing remains constant. Most of the times that the data is changed, the data can be degraded. For instance, editing steps in Photoshop often degrade image data.
Now, the image degradation that occurs at any particular step is generally fairly small. Frequently, the image degradation that occurs at a single step can not be seen unless it is viewed at 100% on the monitor or with a loupe when viewing a print. However, the problem that occurs is that the image degradation is cumulative. The image degradation builds up step after step. So, many small losses of image quality add up to the point where the cumulative loss is noticeable in a print.
The only way to avoid this problem, and to produce the highest quality prints, is to make sure that each step is performed in a manner that produces the highest quality image with the least amount of image degradation possible. This is why optimizing the printing resolution is important. Optimizing the printing resolution is just one of the many steps in the image editing process where we can make sure that we get the highest quality image by using the best methodology available.
WRAPPING IT UP
Once the best printing resolution has been identified, that resolution should be used to make the final print.
Now, it is important to keep this procedure in proper perspective. This procedure is valuable when a print of the highest quality is desired. It is not necessary to carry out this procedure for every print. For instance, if you are creating a 24"x36" print for an exhibition, this process would be very valuable. However, if you are producing an 8"x10" print for your family photo album, this procedure would be overkill.