Preparing bitmap images for 35mm slides
Executive Summary
Images for output to 35mm film should be:
- 24-bit RGB color.
- 4096 x 2732 pixels or less
The Details
For starters, get into the habit of thinking in pixels. Dots, if you prefer. DPI is meaningless unless you know the number of inches, and inches are meaningless unless you know the number of dots. If you know both, multiply them to get the total number of pixels.
For example, if you scan a 4 x 5" photo at 300dpi, your image will be
Tip: Most scanner software and virtually all bitmap editing programs can be set to read in pixels rather than inches and dpi. For slidemaking purposes, it's far easier to do that than to keep a calculator by your side at all times.
Now 4096 x 2732 is a big image. Really, really big. Like 33 megabytes uncompressed. In most cases, there's no reason to create images that big since our film recorder software will scale smaller images up automatically.
However, there are a few things you must do to prepare images for 35mm slides or other film output:
Create your images in RGB color. If your images are already done in CMYK or PMS colors, convert them to RGB before sending them to us. Film recorders are strictly RGB, so your images will be converted at some point no matter what. Here are the questions you should consider:
- Who should convert the images? We can do it for you, but we charge extra for the service. By doing it yourself, you save time and money.
- Who approves the conversion? You know what your image is supposed to look like, we don't. By doing the conversion yourself, you're in control. If we do the conversion, the decisions are left up to our software. Generally the results are good, but may not always be exactly what you wanted or expected.
Use 24-bit color. The files will be larger, but the quality is worth it. 8-bit (or "paletted") images contain only 256 colors. The film recorder can produce millions of colors so why not take advantage of them? The only exception to this rule is screen captures. If they were 8-bit color in the first place, it's best to leave them that way.
"Right-size" your images. The more pixels (the higher the resolution), the sharper and smoother your images will look on film. How far you want to take it is your call, up to a maximum of 4096 x 2732 pixels (that's for 35mm slides … check with us for specs on other size output). The more detail you need to convey, the higher the resolution you should use.
Allow a safety margin.Our film recorders will put the entire image on film, but the slide mount or negative holder may crop the image slightly. If you want to project or print the entire image, leave a margin of safety. Create images at 3800 x 2533 pixels or an even fraction of that resolution. When we shoot these slightly undersized images, we center them on the final slide with a black surround. Here are some typical image sizes:
| Full-frame 35mm | With safety margin | Approx. file size |
| 4096 x 2732 | 3800 x 2533 | 33 mb |
| 2048 x 1366 | 1900 x 1266 | 8.5 mb |
| 1024 x 683 | 950 x 633 | 2 mb |
Consider getting a few test slides made before you create your final images. Film and film recorders reproduce color differently from your screen or printer. Some colors simply don't reproduce the same. Avoid using Pantone or CMYK to specify your colors, as these often translate to RGB in surprising ways and there's little or nothing we can do to correct for it.
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