As for the level of detail, it\'s typical to try to print at 240 - 300 ppi for photos. But you\'d be laughed out of a job if you tried to put a 240 dpi laser printer on your bosses\' desk. 2400 dpi lasers are the norm. Something to think about...
When output resolution is set in Photoshop at say 300 ppi, that indicates how many pixels in EACH COLOR will be printed per inch. Printer makers express resolution in terms of total dots of all colors. So 300ppi in Photoshop x 8 colors becomes 2400 \"dpi\" on the printer. In reality you have overlapping clusters of 8 different colors spaced 1/300th inch apart center-to-center.
The ppi / dpi / DPI terminology gets confusing, but the term DPI originated back in the letterpress printing days when photos were reproduced by etching dot patterns in chunks of zinc with acid. It expresses the spacing of the dots center-to-center. If you take an offset printed magazine and look at it with a 10x magnifier you can see a rosette pattern of CYMK dots.
Ink jet and lasers printers use different imaging methods so you assumptions based on the numerical comparison isn\'t correct. Inkjets spray ink like an airbrush using the spacing of the nozzles on the printhead (360 per inch on Epson), pulsing frequency, and ink drop volume to change dot size.
Laser printers use \"hard\" dots similar to offset printing. Each laser printer halftone is actually checkerboard pattern of smaller dots (e.g, 10 x 10). By fusing toner in 0-100 of those sub-dots each dot in each color can express between 0 and 100% reflectance in 1% increments.
The dots are imaged on the paper 1/10th of a dot at a time ........... in the first pass, ............ in the second, etc, until the 10x10 matrix of each dot in the row is completed after the 10th pass of the imaging head. Its the imaging head that has 2400 imaging cells, but with 10 imaging cells needed for each printing dot the actual resolution of the image in terms of DPI (spacing of halftone dots) is 2400 / 10 = 240 DPI per color x 4 colors = 960 total DPI for all colors.
The weak link in the chain is the resolution of the human eye. Since we don\'t typically look at images with 10x or 50x magnification what matters is what the image resolution looks like at reading distance. Our eyes can\'t resolve more that 240 dots per inch at reading distance so there is a point of diminishing returns in trying to cram them closer together.
Printing works by overlapping transparent ink that absorb some colors of light. You don\'t realize it by you see the image because the illuminant is passing through all the ink layers, reflecting off the paper, and passing back through the ink to your eye. That\'s why paper brightness is a perceptual variable and different profiles are needed for different papers to make color management work.
Where inkjets have an advantage over photo based and halftone based reproduction is their ability to control the tonality more discretely by controlling ink volume with ink head pulsing and spacing, and by using two or more tones of the printing ink so where its not possible to print a small enough cyan dot to express a subtle tonal variation you print a bigger one with cyan ink that is half the strength. It allows the ink to be sprayed on like an airbrush in more of a continuous tone patten than the physical limitations of ink or toner on paper require. Inkjets also have wider gamuts because they can pile more ink on the paper in the saturated tones.
As viewing distance increases the contrast difference between parts of the image becomes more important to the perception of sharpness than dot spacing. Images with fine detail but little contrast turn into blobs of sameness. But an image with dots the size of golf balls can look sharp as a razor if the image is on a billboard viewed from 1000 feet away and there is strong contrast between them. The illusion of hard and soft is a function of contrast. As the shadows in a lighting ratio get darker the lighting looks harder. The same dynamic is in play with images viewed from a distance; the more contrast between two areas the more they will look three dimensional.
So put away the magnifier and find out which printer settings make the your 4 x 6 - 8x10 prints look best overall perceptually from reading distance and for larger prints evaluate them from the distance them will be typically viewed from. For larger images there is trade off. If the file is output for optimal perceptual resolution from 10\' the image will not look as good viewed closer. But if you output your large prints based on looking their best at 18\" reading distance they will not have as much visual impact at 10\'. That\'s due to the way the brain interprets detail and contrast and equates the two.
As for the level of detail, it\'s typical to try to print at 240 - 300 ppi for photos. But you\'d be laughed out of a job if you tried to put a 240 dpi laser printer on your bosses\' desk. 2400 dpi lasers are the norm. Something to think about...
When output resolution is set in Photoshop at say 300 ppi, that indicated how many pixels in EACH COLOR will be printed per inch. Printer makers express resolution in terms of total dots of all colors. So 300ppi in Photoshop x 8 colors becomes 2400 \"dpi\" on the printer. In reality you have overlapping clusters of 8 different colors spaced 1/300th inch apart center-to-center.
The ppi / dpi / DPI terminology gets confusing, but the term DPI originated back in the letterpress printing days when photos were reproduced by etching dot patterns in chunks of zinc with acid. It expresses the spacing of the dots center-to-center. I you take an offset printed magazine and look at it with a 10x magnifier you can see a rosette pattern of CYMK dots.
Ink jet and lasers printers use different imaging methods so you assumptions based on the numerical comparison isn\'t correct. Inkjets spray ink like an airbrush using the spacing of the nozzles on the printhead (360 per inch on Epson), pulsing frequency, and ink drop volume to change dot size.
Laser printers use \"hard\" dots similar to offset printing. Each laser printer halftone is actually checkerboard pattern of smaller dots (e.g, 10 x 10). By fusing toner in 0-100 of those sub-dots each dot in each color can express between 0 and 100% reflectance in 1% increments.
The dots are imaged on the paper 1/10th of a dot at a time ........... in the first pass, ............ in the second, etc, until the 10x10 matrix of each dot in the row is completed after the 10th pass of the imaging head. Its the imaging head that has 2400 imaging cells, but with 10 imaging cells needed for each printing dot the actual resolution of the image in terms of DPI (spacing of halftone dots) is 2400 / 10 = 240 DPI per color x 4 colors = 960 total DPI for all colors.
The weak link in the chain is the resolution of the human eye. Since we don\'t typically look at images with 10x or 50x magnification what matters is what the image resolution looks like at reading distance. Our eyes can\'t resolve more that 240 dots per inch at reading distance so there is a point of diminishing returns in trying to cram them closer together.
Printing works by overlapping transparent ink that absorb some colors of light. You don\'t realize it by you see the image because the illuminant is passing through all the ink layers, reflecting off the paper, and passing back through the ink to your eye. That\'s why paper brightness is a perceptual variable and different profiles are needed for different papers to make color management work.
Where inkjets have an advantage over photo based and halftone based reproduction is their ability to control the tonality more discretely by controlling ink volume with ink head pulsing and spacing, and by using two or more tones of the printing ink so where its not possible to print a small enough cyan dot to express a subtle tonal variation you print a bigger one with cyan ink that is half the strength. It allows the ink to be sprayed on like an airbrush in more of a continuous tone patten than the physical limitations of ink or toner on paper require. Inkjets also have wider gamuts because they can pile more ink on the paper in the saturated tones.
As viewing distance increased the contrast difference between parts of the image become more important to the perception of sharpness that dot spacing. Images with fine detail but little contrast turn into blobs of sameness. But an image with dots the size of golf balls can look sharp as a razor if the image is on a billboard viewed from 1000 feet away.
So put away the magnifier and find out which printer settings make the your 4 x 6 - 8x10 prints look best overall from reading distance and for larger prints evaluate them from the distance them will be typically viewed from. For larger images there is trade off. If output for optimal perceptual resolution from 10\' they will not look as good viewed closer. But if you output your large prints based on looking their best at 18\" reading distance they will not have as much visual impact at 10\'. That\'s do to the way the brain interprets detail and contrast and equates the two.
Chuck
Jan 01, 2010 at 10:47 AM
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