What should be the Original Image Resolution (PPI/DPI) required for Printing a Magazine with FM Screening dot?

We need a minimum of 240 ppi for most print production. 300 ppi is often referred to because it's a nice round number, but the reality is for 150 lines per inch (most print production) you can get away with 240 ppi. And more pixels per inch are never an issue.

 

    Scanners: SPI (samples per inch) or ppi (pixels per inch) PPI (pixels per inch) works for scanner input, but technically, spi is more accurate. For exam - ple, if you scan% at ppi or if you scan at% at ppi , the scanner “sees” or samples the same data. The ppi , when viewed in Photoshop, is different for each file, but the sampling of the original by the scanner is the same. The maximum spi of a given device is capable of is the optical resolution at%. SCAN TIPS Always scan at no more than your maximum optical resolution. This number is not the large number advertised on the box ( dpi resolution!), but the smaller number tucked away somewhere in the specifications. If your scanner has a spi optical resolution and you determine that you need an image resolution of ppi , you can scan at a maximum of% ( ppi x8. = ppi ). If your scanner lists an optical resolution of x, use the smaller number for your calculations. If you determine that you only need ppi for your images, scan at a “native” resolution of your scanner. If you have a spi optical resolution scanner, scan only at, (% maximum enlargement), (% maximum enlargement), or (% maximum enlargement) ppi . Then resize or resample the resolution to ppi in Photoshop after you are finished scanning. Digital Cameras: Width x Height Pixels only A digital camera can capture data based on the mega-pixel ability of its CCD. For example, an 8 mega-pixel digital camera shoots at approximately x pixels (different brand cam - eras may vary in size slightly). pixels * pixels =7,, total pixels (rounded up). Some may refer to the pixel capture size ( mega-pixel) as the camera’s resolution. From a ppi viewpoint, camera images mostly have no resolution assigned to them (although some high- end cameras can set this). However, when you open the file into most image-editing programs, such as Photoshop, a reso lution is assigned to the file. Most programs, including Photoshop, use ppi as a default resolution. It is incorrect to say that digital camera images have a reso - lution of ppi since it is the software program assigning that number.   Copyright by David Creamer 3 www.IDEAStraining.com Monitors: Width x Height Pixels only Monitor resolution is measured strictly by pixel width and height. Some common settings are x,x, and evenx. Different size monitors could be set to the same resolution, so there is no default ppi setting for monitors since ppi depends on the monitor resolution and the physical size of the monitor. For example, ax monitor could be inches (monitor sizes are measured diagonally like TVs) or could be inches, so the actual ppi would be different for each. Some repeat the old settings of Mac monitors displaying at ppi and Windows displaying at ppi , that that standard went away years ago with more modern monitors. This information is inaccurate (since ppi depends on resolution and size, as mentioned) and should not be used. That being said, programs assume a default resolution, so you will still see those numbers used in software, but it does not reflect reality. Web & Video Graphics: Width x Height Pixels only Web Graphics also are measured strictly by X/Y pixels only, usually in relation to a monitor size. Basically, one image pixel of a web graphic displays on one monitor pixel*. A web graphic that isx pixels will completely fill up a monitor set tox, but only fill% of the screen of a monitor set tox. A common misconception is that web graphics have a resolution of ppi , but that is completely inaccurate. An image that isx pixels at ppi will display in a web browser the same size as a graphic that isx pixels at ppi — essentially it will take upx pixels on whatever monitor it is on. *At Actual Pixels (%) in Photoshop also display one image pixel for one monitor pixel. (Many web-only graphics programs do not assign resolution to graphics and work strictly by pixel dimensions.) Video graphics work the same as web graphics except they have some per-determined pixel settings. A standard-definition video (SD) setting for TV isx pixels (surprisingly low resolution compared to print), the high-definition video setting is oftenx (although it varies by type of camera). It should also be mentioned that video may have different shaped pixels; they can be square, vertical, or horizontal. Video editing programs and Photoshop compensate for the different pixel shape by “distorting” the image on screen. Image resolution for printing: ppi (pixels per inch) (If you are new to commercial printing, it may be useful if you read the lpi and dpi sections first, before reading this section.) Excess resolution is not used when printing the file and only does three things: • make your files larger than necessary, • increase the printing time, and • it may have the effect of “softening” your images. The best solution is to have the maximum amount of resolution REQUIRED, based on your final image size, your printing method, and line screen used.   Copyright by David Creamer 4 www.IDEAStraining.com AM (Halftone) Screening For print, images need a minimum resolution, measured in pixels per inch or ppi (this should not be called “ dots per inch ”), in order to have enough detail and look natural. The amount of resolution required mostly depends on lpi (see following section). For example, the resolution required is approximately1.5 times the lpi , although many printers still require2 times the lpi (better printers will give a desired ppi range, such as- ppi ). For example, when printing at lpi (a common lpi for magazines), the image resolution should be ppi (or ppi if using the2X method). If using the1.5x lpi resolution setting, it is important not to scale the image up in the layout program since the image is already at it’s maximum size for optimum quality. Using the2x resolution calculation results in having4 image pixels to1 halftone dot, whereas the1.5 resolution calculation results in2. pixels to1 halftone dot. Technically, the actual requirement for AM screening is1. (rounded) resulting in2 pixels to make1 half - tone dot. When creating the halftone dot, the pixels are averaged for an overall shade of gray and then the corresponding halftone dot is produced in the RIP (raster image processor). Line screens, measured in lpi , have ink dots arranged in a set pattern with different inks printed at different angles; black is usually printed at°, . Since printers can only put down a solid dot of ink, various tones are created by different dot sizes. However, the dots, regardless of size, are always spaced out the same distance (determined by the lpi ). AM Screening Chart Printing Method 1.5 X Method 2 X Method File dimensions:8x in. PPI Size for RGB (in MB) Size for CMYK (in MB) PPI Size for RGB (in MB) Size for CMYK (in MB) Newsprint — LPI 5. 6.9 9. .2 Magazine — LPI 9. .2 .2 .6 Magazine — LPI .6 .4 .6 .5 Brochure — LPI .8 .1 .5 Brochure — LPI .6 .5 .6 .8 FM (Stochastic) Screening FM screening is a comparatively newer technology (AM screening has been around since the lateth century). It uses more of a “random” pattern in “specs” of ink rather than a structured line screen, densely packing more specs in darker areas of color. The result is better quality images since there is more capability of maintaining detail, no moiré or rosette patterns, larger   Copyright by David Creamer 5 www.IDEAStraining.com color gamut (range), and a more photographic look—however, there may be some noise/grain in flat-color areas. FM screening is measured by the specs or dots of ink, ranging from- microns (a micron is . mm or1/, of an inch)—this would be roughly equivalent to – lpi in AM screening. FM Screening Chart Printing Method Resolution File dimensions:8x in. Micron Size (appx.) PPI/PPMM Size for RGB (in MB) Size for CMYK (in MB) Newsprint — micron 1/ in / .4 .9 Magazine — micron 1/ in. / .8 .7 Magazine — micron 1/ in. .5/ .1 .8 Brochure — micron 1/ in. .6/ .3 Brochure — micron 1/ in. .3/ .7 As you can see from the chart above, FM screens are much smaller than AM screens. A micron FM screen can print dots/specs per inch, while a LPI AM screen is always the same ( various-sized ink dots per inch on a fixed grid). Image resolution requirements are hard to pin down for FM screening, so it is best to ask your printer. I based my recommen - dations by opting for higher resolution due to the ability of FM screening to print more detail. I essentially treated FM screening the same as I would ink jet printers—by dividing the micron dot size by an whole number. Inkjet Printing Inkjet printers use a printing method virtually identical to FM screening, except the inkjet companies usually list the resolution of the printer in dpi (for example, the Espon Stylus Photo R prints at x). It might be tempting to print at the resolution of the printer itself, but most print drivers limit the resolution sent to the printer—this is known as the native resolution of the print driver. For example, most Epson print drivers limit output to the printer to dpi and dpi . Luckily, this is usually an even division of the actual printer resolution. (When dealing with printers, just like scanners, work with the lower resolution number.)   Copyright by David Creamer 6 www.IDEAStraining.com To determine the best ppi for images, based it on the native printer resolution—this infor - mation is usually buried deep in the user manual of the printer. As mentioned, Epson print drivers usually print at and dpi , while Canon and HP print drivers tend to use and dpi . However, both the and ppi images are usually overkill, so the and dpi number for your calculations. Print Quality Standard Medium High Inkjet Resolution PPI File Size for RGB 8x in. (in MB) PPI File Size for RGB 8x in. (in MB) PPI File Size for RGB 8x in. (in MB) ,, and DPI 7. .7 .7 ,, and DPI 5. .6 .6 Halftone Screen Frequency: LPI (lines per inch) Using black-only print job as an example, gray tones are mimicked by printing various sized dots of solid black ink at a set distance. A group black dots lets some of the paper show though (usually white paper), and the blackness of the dots and the white of the paper blend optically to look like a shade of gray. Depending on the size of the black dots, the gray looks darker or lighter. However, in a given print job, the spacing of the dots is the same (for AM screening). The spacing is referred to by these names: screen frequency, line screen, or more recently, lines- per-inch ( lpi ). The lpi is usually determined by the type of printer and by the quality of paper. Line screens are easiest to see in a newspaper since the cheap paper requires that the dots be spaced far apart due to dot gain (the ink soaking in and spreading out on the paper). The same principal applies for spot-color printing and process-color printing (CMYK). Printer resolution: DPI Laser printers can print at various settings up to their maximum resolution. For example, a dpi printer could print at dpi or even dpi (printer resolution is the proper place to use the term “ dpi ”. The number of gray levels a printer can mimic is directly related to the dpi of the printer and the lpi used. Using the formula below, we can determine how many levels of gray can be printed at a given line screen at a given printer resolution. (Output Resolution / Screen Frequency) 2 +1 = Gray Levels Gray Levels Printer Resolution LPI LPI LPI 5 3. The extra printer resolution makes quite a bit of difference for photographs. The human eye needs about- gray levels for images to look realistic.