Jerry G wrote:
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.
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.