Lenticular Imaging Process

a) Origination: Any lenticular effect must be created from at least two complete in scale files.
For example, a two image flip (clown smiling; clown frowning) starts out as two separate files, exactly the same size as each other. An animation can incorporate more files, such as video footage or sequential animation cells (up to 50 frames or approx. 3 seconds may be accommodated), which covers the sequence of the proposed animation.

A 3dimensional image works best with at least seven separate sequential parallax views, either photographed using a camera track device, a multiple lens camera, or images created from layered objects in a Photoshop file (Photoshop is a registered trademark of Adobe Systems, Inc.), which are manipulated with a software program capable of moving the objects of each layer in such a sequential way as to produce artificial parallax image frames. More than seven parallax frames, produces smoother and higher quality 3D images. When properly managed in the image output and/or print production process, 24 or more frames may be used to create a spectacular result.

b) Interlacing: The art must be divided precisely among all the lenses that make up the final image. The original images are actually sliced and interlaced together, so that each original image has a raster of image date sequentially placed under each lens. For example a two image flip would be made with one-half of all the lenses containing image no.1 while the other half of all the same lenses would contain image no.2.

The process of interlacing the original files together into a master file, which will match precisely to the pitch (number of lenses per inch/mm) of the lens is performed with a special software program designed to perform that task.

a: In lithographic printing the image is printed directly to the lenticular lens. This requires films to be output from an image setter, or plates made via a high resolution CTP system capable of performing the task. Some systems have software and/or hardware limitations, which determine the Lenticular image quality possible to achieve. Careful selection of equipment and RIP are mandatory to achieve the highest possible quality. Both film and CTP based systems are high resolution processes requiring precise calibration and methods of operation.

b: Other methods of reproduction capable of being used to produce Lenticular prints are digital photographic or inkjet printing devices, where the interlaced master is output as a finished image which then needs to be laminated to the reverse of the lens in a separate adhesive process.

Please note that our lenticular sheets are not designed for these applications (but for litho offset printing to the backside of the lens)

The most common method accounting for over 90% of the lenticular imaging in the world today is direct to lens lithographic printing. From high resolution films, plates can be exposed and positioned in precise register on a four colour process press. Most presses available in this category are in fact likely to be 6 colours, allowing a blanket background white to be printed in the same pass. The mechanical condition for any press used to print Lenticular work, is critical. Colour to colour registration must be maintained to within 1/1000 of an inch for some jobs, and image alignment with the lens must be maintained to extremely critical tolerances, in order to produce the highest possible quality results. The newer press models of most press manufacturers are capable of good to great results.

Usually a more opaque white needs to be added later after the inks are dry; there are many methods of doing this (UV ink, silk screen, laminated cover stock or thermal laminated polypropylene). When printing white ink via offset printing in a separate pass thru the press, it is desirable to use more than one printing unit to print a suitable level of opacity. The use of UV interdeck curing systems greatly enhances both opacity, coverage, and product scratch resistance. It is also possible to print the reverse side with graphics, over the white barrier. In that case, opacity is more critical to achieve a barrier which does not allow the “ghost” of the reverse side graphics to be seen from the front side.

Prepress process:

Software:

•  Photoshop
  
•  Quark
  
•  Illustrator
  
•  InDesign
  
•  ArtPro

  
  Memory (RAM) and processor speed

  • Minimum we recommend is 1GB RAM and 1.7 ghz or faster processor. Dual or more processors can speed job processing, if using software capable of accessing and using the additional processor/s. An Apple G5 with at least 2GB of RAM is an excellent choice. Use maximum RAM on operating unit, and have an additional large capacity Hard Drive as a scratch disk if at all possible. Lenticular files can be enourmous, and imposed layouts (if not done in the RIP), are very taxing on the workstation.
    

  Image setter or CTP:

  • Minimum 300 line screen to achieve reasonable quality, best quality is available using up to 600 line screen. Modulating the screening, to a value mathematically compatible with the actual lens pitch, produces more perfect results. Banding due to interpolation of the image data when creating dots, and other imperfections may thereby be reduced or eliminated. Special screen angles must be used in order to avoid moire’ and/or patterns of coincidence with the linear array of the lens and it’s pitch.
    
    
  • At least 2540 DPI imagesetter or platesetter resolution is needed (Res 100/mm), to produce satisfactory results. Using 5080 DPI (Res 200/mm) will deliver much higher quality results. Most CTP systems operate in the range of 2400 to 3556 (a few models can achieve up to 4000) lines per inch of laser spot resolution. Again, by modulating the actual resolution used to expose film or plates for any job, to a value which is mathematically compatible with the actual lens pitch and the screen set created to be optimal for it, produces superior results. Not all RIPs and/or imagesetters or platesetters are capable of such modulations, and whereas most systems are capable of producing acceptable results; those which are possible to manipulate are capable of exquisite quality. Stochastic screening technology is capable of near photo resolution, and may provide the best possible Lenticular results, but anyone wanting to use a Stochastic method should perform a careful patent search before electing to use it.

  Film:

  • Standard film is .004″ thick, while .007″ film is recommended for dimensional stability. Note: When converting to .007 film from .004, the laser heads may need to be recalibrated. Likewise, whenever using high resolutions, the proper laser resolution intensity values need to be established and setup, and exposure curves created, to produce linear reproduction of dot values.

  Proofing:

  • We have found that 3M Imation match print system is the best. It is extremely stable whereas other systems such as Fuji are guaranteed to expand and contract requiring compensation. Commercial grade Imation paper is good while ‘Low Gain’ Imation stock is excellent, sometimes better than what is achievable on press.
    

A. File Preparation:

Depending on the type of effect desired you must determine the number of files to create in order to illustrate the effect. For example, a basic flip (one image changing to another image) is simply two files. An animation can be any number of files ranging from two (a flip) to a series of 50 (above 24 is extreme, but possible) depending on the type of action and the number of files which would work best for that animation. A morph is considered an animation, and 7 to 20 frames are appropriate. A 3D image would require at least 7 parallax frames, while we recommend approx. 20 frames if your equipment is able to manage the data and output. Whatever the final number, all the files must be scaled to the exact same size and resolution before interlacing.

Sufficient image size must be built into the artwork when generating 3D, where the viewing angle will require extra parallax (horizontal) data for background objects and backdrop. The image file resolution is determined by the three variables of a) the lens pitch, b) the number of files you are using, and c) the output capability of your image setter. For example, a 75 LPI lens (75 lenticules per inch) employing a 12 frame animation or 3D image requires a pixel count of 900 per inch (75 x 12 = 900). To transfer this digital data accurately to film or plate and finally to the lens substrate, you must decide what screen values will be used for printing, and which imagesetter or platesetter resolution will be used for the imaging process. In a system capable of operation at variable resolutions and screen sets, you should always use whole numbers, when calculating all the values to be used. For example an interlaced file at 900 pixels per inch, cannot be printed at 900 line screen on press, so you must use a “file to dot reduction ratio”. It is possible to print up to 600 line screen, so the ratio of 2 : 1 is possible, or 450 line screen. In order to generate smooth color gradations in the image, it is important to use the highest imagesetter or platesetter resolution possible to work with 450 line screen.

Dot percentages and film or plate output device resolutions work much like colors in a computer monitor and computer graphical display interface card. The more bits of data there are per color in the file and used by the display card, the more colors can be viewed on the monitor. In an imagesetter or platesetter, the more laser spots used to form each print dot, the more “gray shades” there are for each color when printing, and therefore viewing the printed piece. The more gray shades there are, the smoother the transitions between differing dot percentages.

Printing dots are made by exposing spots on the surface emulsion of film or plate with a laser beam. Screen angles are created by exposing a different pattern of laser spots for each dot, for each color, for each dot percentage value. For example a 50 % dot of magenta is formed by a cluster of laser spots, in a different “zone” and shape than a 50% dot of cyan. Each “zone” is considered to be a “dot matrix” area, which is the same matrix used for all colors. The more laser spots used to expose a full matrix, the more gray shades result. The dot formations (clusters of laser spots), are calculated by the hardware “color data processor” as the Rip sends the exposure data to the output device, or in some Rips, that task is performed when it processes the job data in the “Rip process”, thereby building an “exposure map” at the same resolution the output device will expose film or plate. In the latter case, the exposure map (which is a 1 bit tiff file) will command the laser to either make a laser spot or not, for each consecutive area of the “dot matrix”. With a properly calibrated output device, it is possible to expose any combination of laser spots and make any pattern, from no image to completely solid areas, and anything in between. Actual screen values achieved by using a matrix of 10 x 10 (100 possible laser spots per dot being formed), yield incremental values of 1%, or 100 gray shades per color. If a matrix value of 6 is used, then only 36 possible gray shades per color are achieved. The exposure resolution to be used is therefore paramount to high quality print results.

The best way to achieve great Lenticular results is to use the highest possible output resolution, which is a multiplier of the line screen which will be used. In the continuing example, 450 line screen, multiplied by the largest whole number possible within the capable resolution of the output device, is one of the following:

If the output device is capable of up to 5,080 lpi resolution, then it is possible to use a “dot matrix” value of 11, which produces up to 121 gray shades per color, at 4,950 actual resolution.

If the output device is capable of up to 3,556 lpi resolution, then is is only possible to use a “dot matrix” value of 7, which produces 49 gray shades per color, at 3,150 actual resolution.

Should your imagesetter and/or Rip be incapable of operation using customized resolutions and screen sets as described above, you must interlace your files using the resolution required by multiplying the lens pitch by the number of frames used, and then the interlaced file can either be Ripped at the same resolution (preferred), or at a “file to dot” reduction ratio, equal to the screening chosen for printing, and then output using the highest resolution available on the output device, using a screen set of 350 or greater lpi. When this is required, the file and dot resolutions are subject to “interpolation” when forming dots from the image file, which appear as “banding” in the viewable image. Such banding may be only slightly noticeable, or may be very noticeable, and detrimental to job quality.

B. Interlacing:

Interlacing is the process of taking the data from the individual images or artwork frames, and reorganizing it to fit precisely into the lenticules which make up the lens array of the lenticular sheet. It is best to explain this process with a simple example such as a basic flip image. The technology of lenticular is based on the ability of the lens to magnify data, which has been placed underneath it. There is room on the backside (printing surface) of the lens to place a lot of image data. In the case of a basic flip, we only need to put two bits of data, each representing one of the two images selected for interlacing, side by side (sliced together) under each lenticule. Since we have determined that the lens sheet we are planning to print is approximately 75 LPI, we know the width of the lens is about one-seventy-fifth of an inch (or approx. .0133″). Interlacing must be done at the exact “optical pitch” of the lens.

In order to determine the exact “optical pitch” of the lens; a pitch test must be performed, by either laminating, or printing a series of sequential pitch patterns onto the lens surface, and then reading the results. It is always best to perform the test using the actual method to be used in the print production process. If the job is to be printed on an offset printing press, then it is best to print the pitch test on the same press, using the same physics and ingredients that will be employed in actual production. It is only necessary to print the test with one color ink, but the press should have all print units on impression, and in blanket contact as if printing. The test plate should be on either the second or third print unit which will be used for printing ink on the live job, and all other print units ahead of it also on impression with normal printing pressures.

The pitch test must be performed with the pitch patterns in close parallelism to the Lenticular lens array. Following the application of the image, you must view the results from the front side, at the viewing distance appropriate for viewing the real finished job (some jobs are intended for close up viewing and others for more distant viewing). By orienting the lens horizontally, and suspending the sheet at the appropriate viewing distance, then by moving the lens sheet and therefore image plane, perpendicular to the direction of the lenticules, you will see the patterns change from being present to clear. Some of the patterns will appear to be differing sizes of clear and colored blocks, and some will appear to be nearly all color, changing to all clear. The pattern which “clicks” completely on and off over the entire surface of the pattern, is the correct “optical pitch” for the job. As for example the test proves the actual optical pitch to be 75.59 lpi, then you will interlace a simple two flip image at 150.98 ppi (pixels per inch).

The best way to perform the interlacing is to use special interlacing software. There are several programs available (see www.lenticular-software.com), capable of doing the job of both interlacing, and also scaling the images or image frames to the appropriate size for the job, without the need to do that task separately. The images or image frames must however be exactly the same size and resolution as each other, in order for the interlacing to be done.