Electronic/Digital/Video Display

The 300KB file size is primarily for electronic display use on a video monitor, i.e. publishing on the World Wide Web or a small group presentation via computer. This file size (about 384 x 256 pixels) will produce a 5.3" x 3.5" image (@ 72 ppi) on a VGA monitor, filling about 1/3 of the screen.

The 1.1MB file size (about 768 x 512 pixels) has enough resolution, even when cropped, to completely fill a standard VGA screen (640 x 480 pixels).

When converting our digital images files to 35mm slides (via a film recorder), use the 300KB for no more than 1/8 of a frame; use the 1.1MB for no more than 1/4 of a frame; and use the 4.5MB for full frame 35mm slides. Larger use of these files may result in a "pixelized" look when projected.

Print Reproduction

Screening, over-sampling and separating. Print reproduction comes in many forms, from personal laser printers to four-color offset printing. Many "Printing on Demand" options are also available. Most of these printing methods require you to set a halftone "screen" frequency for the digital image in a graphic layout program like PageMaker or QuarkXPress. The frequency of the screen pattern (measured in lines per inch [lpi] or in dots per inch [dpi], by the layman) determines the smooth or coarse appearance of the printed image.

In the past, the rule of thumb has been to use two pixels from the digital image for each line screen or halftone dot reproduced on the printed page. This process of "over-sampling" is required to provide maximum sharpness and remove the square pixel shapes (pixelization) in the final reproduction. Recent studies have shown that an over-sampling of 1.5 pixels per printed dot (lpi or dpi) is more than adequate to produce good sharpness. And a file based on a 1.5:1 over-sampling ratio is almost 1/2 the size (56%) of a file based on a 2:1 ratio --allowing for faster file transfer and "RIP" processing times at your service bureau. The table below is based on a 1.5 to 1 over-sampling ratio.

For 4-color reproduction, the digital RGB (Red, Green and Blue) image must also be separated into the four printing colors: Cyan, Magenta, Yellow, and Black --also known as "CMYK" or "4-color "separations". This separation process is usually done in a image editing program like Photoshop.

Printed Image Sizing Table

This table shows the maximum printed image sizes that are possible from several standard digital image file sizes, using various halftone screen frequencies (based on the 1.5 to 1 pixel to halftone dot over-sampling ratio described above).

Definition of Terms: The terms "dots per inch" (dpi), "pixels per inch" (ppi), and "lines per inch" (lpi) are often used interchangably, causing much confusion and many errors. To set the record straight, and for the purposes of this discussion and the table below, ppi refers to the pixel frequency of the digital image; dpi refers to the actual resolution of the output device (i.e. a laser printer or image setter); and lpi refers to the frequency of halftone dots on the printed image.

                     PRINT SIZES POSSIBLE WITH THE FOLLOWING HALFTONE DOT FREQUENCIES
                       --and the pixel frequency (ppi) you must set in Photoshop.
Halftone frequency:  55 lpi    65 lpi    85 lpi   100 lpi  133 lpi  150 lpi  175 lpi
--set image ppi to:  83 ppi    98 ppi    128 ppi  150 ppi  200 ppi  225 ppi  263 ppi
-------------------------------------------------------------------------------------
DIGITAL IMAGE SIZE                     MAXIMUM POSSIBLE PRINT SIZES
 file   resolution
 size*  in pixels    (inches)  (inches)  (inches) (inches) (inches) (inches) (inches)
-----   -----------  --------  --------  -------- -------- -------- -------- --------
300KB   (384x256)    4.6x3     3.9x2.6   3x2      2.6x1.7  1.9x1.3  1.7x1.1  1.5x1

1.1MB   (768x512)    9.3x6.2   7.8x5.2   6x4      5.1x3.4  3.8x2.6  3.4x2.3  2.9x1.9

4.5MB   (1536x1024)  18x12     15x10     12x8     10x6.8   7.7x5.1  6.8x4.6  5.8x3.9

18MB**  (3072x2048)  37x25     31x21     24x16    20x13.7  15.4x10  13.7x9   11.7x7.8

**This file size is only available through our extended price list.

Halftone Screen Applications. Check with your service bureau or printer to find what dot/screen frequency they are capable of reproducing:

55 lpi -- Maximum halftone frequency produced by 300 dpi personal laser printers.

65 lpi -- Halftone frequency used in some low-quality newspapers (or newspapers using older printing technology).

85 lpi -- Maximum halftone frequency produced by 600 dpi laser printers, and the halftone frequency used in most newspapers and some medium quality newsletters.

100 to 120 lpi -- Halftone frequency used in some newsletters and some high quality newspapers. High-end, 1200 dpi laser printers are capable of producing this halftone frequency. Many short-run "electrostatic" printers use this halftone frequency.

133 lpi -- Halftone frequency used in most magazines, books, and better quality newsletters printed on 4-color offset presses; and short-run offset "web" presses used for flyers and brochures.

150 lpi -- Halftone frequency used in standard quality brochures and "high-gloss" newletters printed on 4-color offset presses.

175 lpi -- Halftone frequency used for very high quality 4-color offset printing.

Custom Instructions: To double check accuracy and to determine other file sizes and dimensions, take the halftone frequency (lpi) of your printing system and times it by 1.5. This is the "over-sampling" factor (in ppi). Now take the digital image dimensions (in pixels), one dimension at a time, and divide it by this factor. This will give you the maximum dimensions of your printed image.

You can also determine the digital image file dimensions need to produce a particular size printed image by multiplying the print dimensions by the "over-sampling" factor. For instance, a 3" x 4" image printed on a 133 lpi web printing process would need a 600 x 800 pixel digital file (133 x 1.5 x 3 = 600, and 133 x 1.5 x 4 = 800).

Interpolation: It is also possible to "fudge" a little, and make your printed image a little larger than the sizes shown in the above tables by the use of image "interpolation". This is done by making the digital image size larger in an image editing program like Photoshop, using the "/Image/Image size" menu. (Be sure to keep your general preferences set to "bicubic interpolation" and to interpolate before performing CMYK separation). Interpolated file dimensions should not be increased by more than 50%. Any increase in file size by interpolation will decrease the sharpness of the printed image, but experimentation will often show that this loss is often minimal. Display prints are one exception to this rule. Large and attractive display prints can be produced using much greater degrees of interpolations, because (1) viewing distances are greater, and because (2) the "scattered" dot pattern used by most ink jet display printers tends to hide some of the sharpness problems.

NOTICE. The digital image file you receive from The Stock Solution (TSS) may vary somewhat in size and dimensions (due to varying film formats and their different aspect ratios). TSS cannot be held responsible for any accuracies in the above table that could cause mistakes in your final product. We suggest you check the actual digital image dimension of the file you receive and follow the "Custom Instructions" if exact accuracy is required in your final printed project.

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