Jerry G Loc: Waterford, Michigan and Florida

I have been considering buying a printer for photos and have been confused by stated resolutions.
When the resolution is 9600x2400 what does the 9600 mean and what does the 2400 mean? I don't believe it is 9600 in along one axis and 2400 along the other. I have searched here and Googled it but haven't found anything that explains it so that I can understand.

Ysarex Loc: St. Louis

The figures are DPI --- dots per inch. And you guessed it; that difference is horizontal/vertical. The printer is capable of 2400 DPI (claimed) as the paper is stepped through the printer and capable of 9600 DPI (claimed) as the print head moves across the paper. (Could be the other way around but I don't think so). You'll encounter the same situation with some scanners. I think physically it's a function of the print head being bi-directional (spits ink back and forth) while stepping the paper through the print is one direction only.

Makes it interesting to consider what's happening if you set the printer to a DPI that's above the lower figure. If the lower figure is sufficient (and honest) I'd pay attention to that and not worry about the other one.

CPR Loc: Nature Coast of Florida

Printer paper is 8 1/2 by 11 so it's fairly easy to see that the higher number is the number of lines that may be printed and the smaller number is the number of ink dots on one line. Most of the time you will set the printer to 300 to 600 dpi and the photo will be quite nice. Printed text lower, perhaps 150 to 300.
I've set my Epson for 2400 once to scan a tiny photo and in scanning or printing that takes a long time.

Longshadow Loc: Audubon, PA, United States

"Lines" as in rows of dots?

burkphoto Loc: High Point, NC

The true printed resolution in that example is 2400x2400, but the 9600 comes from the stepper motor in the printer being able to advance the paper in smaller increments. That allows some smoothing of the image that subtly reduces various image artifacts. BUT, do not confuse printer resolution with image resolution.

In understanding digital printing, it is important to understand the difference between DOTS, SENSELS, and PIXELS. They are completely different concepts.

A DOT is either a spot of ink or dye placed on paper, or a "cell" of a grid defined by a scanner driver that will process scanned dots into pixels in an array of an output file.

A SENSEL is a single photoreceptor on a sensor. Each sensel is covered with a filter — red, green, green, blue (yes, there are usually two green sensels for every red and blue one). The output of sensels is analog voltage, which is converted into digital numbers. The processor in your camera, or in the software on your computer, then creates pixels by combining the color values of a group of adjacent sensels into ONE RGB pixel in the output file, using very complex algorithms. Adjacent pixels in the output array may be derived from some of the same sensel values.

PIXELS are just numbers. They contain the values of red, green, and blue for every discrete picture element (derived point of light) in the image file.

Printers use ink dots or dye spots to reproduce pixel values as colors. Most printing processes are SUBTRACTIVE. They subtract color from white light bouncing off of paper, which is why we print cyan to reproduce "negative red," yellow to reproduce "negative blue," and magenta to reproduce "negative green." Black (the K in CMYK) is added to improve contrast, and with inkjet photo printers, several other colors are used to reproduce a broader range of tones (wider color gamut) than CMYK can achieve.

When you have 240 or more *pixels* from the image file — as processed in the camera or software — spread over each linear inch of printed output, your eyes will merge them together at a distance of about 13". 12.8" is the diagonal dimension of an 8x10 print. At closer viewing distances, MORE resolution is required for the same effect, while at greater distances, LESS resolution will suffice.

The printer's device driver does the conversion from RGB file pixels to whatever array of colored dots or spots is required to produce an image on paper.

You will notice when shopping for printers that the larger pro machines will have a lower maximum resolution than some of the small desktop printers. That is because, again, larger prints require less resolution at reasonable viewing distances. It is also because (for example) a 2880x1440 dot resolution print takes FOUR TIMES longer to print than a 1440x720 dot resolution print. (Both, of course, might be printed from the same exact 300 PPI input file!)

Rest assured that any true photo printer on the market today is quite capable of faithfully reproducing the pixels in your files. HOWEVER, for that to be the case:

> Choose a *computer monitor* that can reproduce at least 100% of the sRGB ICC color gamut. 100% of P3 is even better, and 100% of Adobe RGB is even better than P3.

> CALIBRATE and PROFILE your monitor monthly, using a kit from Datacolor or X-Rite. The international standard for color accuracy must be referenced by your monitor for it to be honest, relative to your printer. Follow the calibration kit's recommendations for initial monitor brightness, contrast, and color temperature, then set gamma, black point, and white point, and let the software do its magic to calibrate and profile. It sounds complicated, but it is super-easy, and it really is something you CANNOT achieve with your eyes.

> Use the correct ICC profile for the exact combination of paper, ink, and printer model in use. Printer manufacturers supply profiles for THEIR ink and paper in the driver software. Load the driver, and the generic profiles are there. Third party paper manufacturers place generic profiles for various printers and OEM inks on their websites, along with instructions for installation on a Mac or Windows computer.

>Using the correct profiles for the monitor, printer, paper, and ink is what allows you to achieve, "What I see on my monitor is (almost exactly) what comes out of the printer" color.

I'm sure that's a lot more than you wanted in response to your question, but if this information helps you or another reader understand what professionals must consider daily, it's worth it.

Jerry G Loc: Waterford, Michigan and Florida

That is exactly what I wanted in a response, some of it I already knew but having it all together was great.
Having worked in lab that processed and printed Color film I already understood and use monitor calibration and printer and paper profiles. It really was the difference in resolution along different axis that I had trouble with.
Thank you.

burkphoto Loc: High Point, NC

TriX Loc: Raleigh, NC

T

That’s a great overview Bill - ought to be a sticky in the printing section.

Strodav Loc: Houston, Tx

Excellent description as usual. No question, you are the guru. How about tackling screening, i.e. reproducing lower resolution rgb pixels with higher resolution cmyk dots.

burkphoto Loc: High Point, NC

Thanks!

FM (frequency modulated dot pattern) screening just spreads the little 2-3 picoliter dots farther apart for light colors and moves them closer for darker colors. Inkjets typically use FM screening. The printer driver converts whatever PPI it has available in the file being printed into a fixed standard resolution (360 or 720 PPI on Epsons), then converts that to the 2880x1440 or 1440x720 dots of ink output. HOW it does it is proprietary, and really unimportant to users. THAT it does it IS important to us.

Many traditional press printing processes use AM screening. The dots are in a square grid pattern. Each dot is created from some number of smaller ink spots.

It has been 20 years since I was involved with offset pre-press prep, so I'm no expert on that. The industry has seen a sea change in technologies since 1979 when I walked into a yearbook printing company and joined their team. There were no PCs or Macs then. Everything was based on photographic processes. By 1998, all the pre-press prep was computerized. By the mid-2000s, they were creating the plates on press. A bit later, they were printing electronically.

tcthome Loc: NJ

kelso007 Loc: Circle Pines Minnesota

Thank you for the explanation!

howIseeit Loc: Kootenays, BC Canada

Now that is an excellent explanation for us newbies!
Thank You! Worth sawing it, I am sure the OP will appreciate the info.

Toment Loc: FL, IL

Thanks! 👍👍👍

FotoHog Loc: on Cloud 9

Thank you for your professorial presentation! Made me fee like I was back in the lecture auditorium again. . .