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Tutorial: Scanning Resolution
At Pixmonix, we can scan your slides and negatives at one of two resolutions - 2000PPI and 4000PPI. What does this mean?
Digital images are composed of pixels. A pixel is one small point of color. When thousands of these very small points of color are put close together, an image results. The image on the screen you are looking at is composed of pixels. If your monitor is about average in size, there are about 800,000 pixels on the screen in front of you. Each pixel is able to show one of more than 16 million colors. When many pixels are placed close enough together and they can convey a wide enough range of colors our eye can no longer perceive the individual dots. Rather, we see a continuous picture.
The resolution of a scanned image refers to the number of pixels in the resulting digital image for each square inch of the original material. The scanning resolution and the size of the original being scanned determine the dimensions of the resulting digital image, measured in pixels. Scanning resolution is commonly measured in pixels-per-inch, or PPI.
For example, if you have a 1 inch square original image (slightly smaller than a 35mm slide or negative) scanned at 4000 PPI, the result is a 4000 pixel by 4000 pixel image (or 16 megapixels). This is similar to the number of pixels in images shot with high-end digital single-lens reflex (SLR) cameras available today.
Not all scanners are created equal. Some scan at higher resolutions than others. However, this is not the only factor to consider when deciding which scanning service or which scanner to use. Scan quality is not the same across different scanners even if resolutions match. Steps taken during and after scanning can have a significant effect on the quality of the final digital images.
In general, you want to scan your slides or negatives at the highest resolution possible, as long as you understand a number of important issues up-front.
The table below details the print sizes and storage requirements for various scanning resolutions.
For many of our customers, the most important figure in this table is the print size possibilities. At 2000 PPI, a scan from a slide can be printed reasonably large (up to approximately 6" x 9"). Going to 4000 PPI allows for larger print sizes (assuming that the source slide or negative is of high enough quality to realize a benefit from scanning at the higher resolution).
At what resolution should I scan my slides/negatives?
We are asked this question quite regularly. The answer is "it depends". For many people who don't plan on making large prints of their images or doing heaving editing or cropping of the digital images, scanning at 2000 PPI is sufficient. Additionally, much of the film that we see at Pixmonix was not shot on the best equipment or stored in ideal conditions. However, we do have many customers who have excellent photos shot on good film with good equipment and technique that benefit from higher resolution scans. On the other hand, scanning at the higher resolution doesn't cost much more and most computers can manage the larger files. The choice is yours. We are always happy to help you determine the right scanning resolution for your project. We are waiting to hear from you!
The examples below show the differences in the scans for a variety of scanning resolutions and processing options. We will add additional examples soon to show slide processing (including Kodachrome) and B&W negative scanning.
In each case, you may click on the small image to see a full-sized JPEG version of the images (saved with very little compression). This will allow you to download the example scanned images and evaluate the effect of the changes in scanning parameters yourself. For example, you may want to try printing one or more of the images. Note that the full-sized images are large - from approximately 2MB to 8MB and will take considerable time to download if you are using a dial-up connection to the Internet.