Mar 14, 2012 6:52 AM
In another thread someone mentinoed pre-sizing image data to prepare it for best printing.
For a long time it's been "standard advice" to resize images so that the ppi is an even division of the printer's dpi, because some years ago occasionally one would run across printers that would produce poor results if you didn't - you might see jaggies in straight edges for example.
Thing is, computers have (not so) quietly been getting more powerful over time, and printer makers have been competing with one another to try to make their printers produce better results than the other guys. One way they've done this is by improving the quality of the algorithms in the printer drivers. Use of mega storage and high accuracy math, which was once taxing on older computer systems, is now standard practice.
So it's time to question the old rule of thumb.
Making a few assumptions about the many variables (what printer, what OS, what version of drivers, what application being used to print) , there seem to be several questions here:
1. Can the image resolution be too high, causing the printer driver to make bad decisions about what ink dots to lay down where on the paper?
2. Does it help or matter if the image PPI is an even division of the printer's DPI?
As I have done in the past, I set out to do some actual testing, to see if I can actually SEE anything to help answer these questions.
I created a sharp image to be printed at 3 x 2 inches: http://Noel.ProDigitalSoftware.com/ForumPosts/Ghirardelli.jpg
Then I printed it at 6 different resolutions (1000, 720, 567, 300, 200, and 100 ppi) by resampling the image, labeling it, printing from Photoshop CS5, and feeding the same sheet of HP Premium Plus photo paper through my older HP 932c inkjet printer 6 times. The printer was set to its highest quality settings, including 2400 x 1200 dpi mode. This was the result:
I then looked critically and as objectively as I could at the different images. Here are my observations:
- The four highest resolution images (1000, 720, 567, and 300 ppi) all seemed to have an equivalent high level of crisp detail.
- I could not detect the inkjet dots. Smooth objects look smooth.
- I could see significant reduction in the finest details in the 300 ppi print vs. the three higher resolution prints, and a slight reduction in the 567 ppi vs. 720.
- At no resolution were any jaggies or evidence of aliasing visible.
- The inkjet dot pattern was plainly visible, and it does differ between the different prints. But it was not possible to say whether one was "better".
- Things seem to have a little more texture in the 1000 ppi print vs. the 720 and 567 ppi prints.
Lacking a high resolution scanner, I took photographs of the 6 different prints. Unfortunately, I didn't have the time to set up with my best lighting and lens combination, so I got some reflections off the glossy paper, and and at this resolution I can't really see the inkject dots in the photos. I want to repeat this when I can find more time to do it better. As I did these photos hand-held, I believe the variances between them could be slightly influencing the results. But I'm going to post them anyway, for you to see.
- I could see ever so slightly more detail in the 720 ppi print vs. the 1000 ppi print, though from the size of the tiny dust/light reflections I think it may have just been the better focused. Note that this observation is not supported by direct observation through the jeweler's loupe, above.
- The 1000 ppi and 567 ppi prints seems to have slightly more noise or texture than the 720 ppi print. Again, this might be issues introduced by the photography process, though I did note a possible increase in texture in the 1000 ppi print with the jeweler's loupe as well.
- Beyond just the blurring, I could see some evidence that straight lines are not quite as straight in the lower resolutions (300 ppi and lower). This seemed more apparent than with the jeweler's loupe examination, and I wonder whether the Photoshop downsampling process could have introduced it.
Left to right, top to bottom: 1000, 720, 567, 300, 200, 100:
Printing to my HP 932c inkject printer on Windows 7 x64
- 300 ppi is not sufficient to coax the best possible detail out of an inkjet printer. It appears a number in the vicinity of 720 or more is better, and this number could be much higher with modern very high resolution printers (mine's old).
- Speed was no different in printing any of these - a modern computer can process a huge amount of data in the blink of an eye.
- When a sufficiently high resolution image is printed (in this case 567 ppi or higher) I saw virtually no evidence that a particular ppi value is superior, for example an even division of the printer's dpi, though in hindsight I realize I should have prepared a 600 ppi image (duh). I will add a 600 ppi image before I re-photograph the results.
- It's possible ever so slightly more texture becomes visible at 1000 ppi than 720 ppi, but it might be just noise.
- Practically speaking, from looking critically at the results I could not see a reason to pre-size the image for a specific ppi value.
I encourage you to experiment and report your results with your particular combination of gear.
Your comments are welcome!