Date: 17 February 99

Subject: How to "Page Size" Bitmaps for Polaroid Palette Film Recorders

The purpose of this Tech Note is to provide a guide for obtaining the correct aspect ratio image for the format of the film you are exposing on your Polaroid Palette film recorder. Using these methods will help you avoid using interpolation (fabricating data) to correct the size the image. Following this procedure will ensure that you obtain the sharpest output possible by utilizing Polaroid’s programmable resolution feature of the Palette color film recorders.

ISSUES: How do I resize an image to fill my Palette's aspect ratio? I do not want any borders and I do not want the image to appear distorted on the resulting Palette exposed film. Is there something I can do during scanning to prevent this? What if I already scanned and retouched my image file and I simply need to resize it for the film recorder's aspect ratio?

For 35mm, the aspect ratio is approximately: 3:2

For 4x5, the aspect ratio is approximately: 5:4

For 6x7, the aspect ratio is approximately: 7:6

SOLUTIONS: Below are 3 options to correctly size your bitmaps for film recorder output. These methods may vary depending on the scanner used and the aspect ratio of the existing bitmap images being used with the Palette film recorder.

Option I. The best way to size your bitmap files for Palette film recorder output is to scan them in the resolution you'll need for output. Scanning for output is always the best method, but not always possible. Refer to the Optimum Input Resolution Guide (see Figure 2) for the correct pixel dimensions for the resolution you want to output. If you have already scanned, this option may not be feasible.

Option II. Very often the image does not have the correct pixel dimensions (or aspect ratio) to fit on the film type you are exposing with the Palette. This brings up an important issue: Many people are concerned with having enough dots-per-inch (DPI). The higher resolution you can scan an image at, the better the detail will be maintained from the original photograph to the final output. This is true, up to the maximum resolution of the output device. If your film recorder cannot resolve your bitmap image file's resolution, you may be scanning and storing too much data. Again, refer to the Optimum Input Resolution Guide (see Figure 2) for scanning resolutions that match your Palette film recorder's capability.

Do not confuse pixel resolution and DPI. When you scan an image, you scan in with DPI, but it is just to form a relational measurement when dealing with input resolution. When you are outputting with a film recorder, pixels are what you are actually dealing with. It does not matter how many Dots per Inch (DPI) you designate to your image file. The film recorder is only concerned with how many pixels make up the image, and this should remain constant no matter how many Dots you designate per Inch (unless you are interpolating the image.) Conversely, you do not need to be concerned with how many inches tall and wide the image is. Again the Palette film recorder is only concerned with pixels and the inches can be changed depending on how many DPI is designated. The pixels remain constant. You are dealing with electronic media and film and DPI is a concern for print media only.

There are two adjustments that can be made to your bitmap image file in an application program like Adobe Photoshop:

1. Crop the image to the correct size using a "cookie cutter" technique. The properly sized image piece is cut out of the original image file without any interpolation. The draw back here is that some of your original image must be discarded to achieve a certain aspect ratio for the output.

2. Create a border around the image that has the proper aspect ratio for the Palette film recorder. This involves creating a file in Photoshop with the correct aspect ratio for the output, and then pasting your original bitmap on top of this border file. This is a way to avoid discarding any part of the original image while maintaining the original aspect ratio. Palette Export automatically performs the equivalent of this function for you.

Cropping the image:

• Make sure the image is in the landscape orientation by rotating (if necessary). The image should be wider than it is tall. Use Photoshop's rotating tool for this.

• Double click on the crop tool to obtain the Crop Tool Options window (see Figure 1).

• Click on the fixed target size box and enter the aspect ratio (in inches) that meets or exceeds the largest dimension of your image.

Example: If your image measures 5 x 5 inches and you are exposing 5 x 4 film in your Palette film recorder, and you do not want a border, you'll need to crop the image to correctly fit the film's aspect ratio of 5:4. In this case, enter 5 for the width and 4 for the height of the Crop Tool Options windows (see Figure 1). Remember to leave the Resolution box empty. When drawing the crop tool, notice that the 5:4 aspect ratio is maintained regardless of how you move the crop around. Because the original image is not the correct aspect ratio, you must sacrifice part of the image. When your area-of-interest is inside the crop area, click inside the crop and "cut" the piece of the file out of the original. The resulting image will have exactly the same resolution as the original file, and now has the exact aspect ratio to expose 4 x 5 film without leaving any borders. No interpolation was performed, you simply "cookie cut" the desired piece out of the original file. You can verify the correct aspect ratio in Palette Export's preview window (Mac only). NOTE: The Windows version of Palette Export has no preview feature.

Here are the approximate aspect ratios for the film types exposed on Palette film recorders:

For 35mm the aspect ratio is: 3:2

For 4x5 the aspect ratio is: 5:4

For 6x7 the aspect ratio is: 7:6

Another, more precise method of cropping requires some calculations:

• Make sure your image is in the landscape position by rotating it, if necessary.

• In Photoshop, select Adjust> Image Size and select pixels for the units.

• Record the pixel width for this particular image.

• Calculate the (height) pixel dimensions you will need to apply. This will depend on the format of the Palette film you will be exposing.

Example: Let’s use 35mm format this time. If your pixel width is 3452, then you multiply 3452 by 2 and divide the result by 3. That equals 2301. 2301 pixels is your height for this particular image and will give you the 3 to 2 aspect ratio you need for 35mm format.

• Returning to the Crop Tool Options box. Instead of using inches, you can set the units to pixels. Plug in the numbers. Width = 3452 Height = 2301

• Draw the desired crop and cut out the area-of-interest from your image file. NOTE: Some interpolation/decimation may occur if you do not draw the crop across the entire width of the image file.

Option III. One can create borders around images to force them into the correct aspect ratio while avoiding stretch distortion. This method is particularly useful when using Palette for Macintosh (SiPA) to image your bitmap files to your Palette film recorder. Borders are sometimes undesirable but unavoidable. If the entire image must be on film and image distortion is undesirable, but the aspect ratio is incorrect for the selected output film, borders are the only way! Borders can look very nice and the big plus is you will not have to sacrifice any of the image. Also, you can get creative with your choice of border colors and adding annotation in the border area. This is how it is done:

Creating a border:

Using the Canvas tool in Photoshop, place your image onto a 3:2 aspect ratio canvas for 35mm format.

EXAMPLE: If your image measures 5 x 4 inches, go into IMAGE>CANVAS SIZE

• Make sure to select the center box in the Canvas tool.

• Type in 6 for width and 4 for height. (6 x 4 inches has an 3:2 aspect ratio and it is a multiple of 3:2). This image will fill the film area top to bottom, and left and right as necessary. No distortion will happen.

NOTE 1: You can select any (border) color for the canvas. Even text can be added to the canvas. Setting the canvas to black makes it disappear on chrome (positive) film. The canvas color must be chosen before you go into the canvas tool. The bottom square on the Photoshop toolbar represents the color of the canvas. You can change the canvas color by simply clicking on this square.

NOTE 2: Palette for Macintosh (SiPA) has the ability to automatically resize your image horizontally and vertically to fit your film recorder's aspect ratio. No adjustment to the image is necessary, however some distortion (stretch) can be seen in the resulting exposure. Palette Export has the same capability to automatically resize your image, but does so only in the horizontal (width) dimension while maintained the original aspect ratio in the vertical (height). Palette Export will leave a black border.