If you want to scan once and never again, it's critical to have the right settings in the first place.
There are four general scanner settings to consider: DPI, color depth, color/grayscale, and image format. Based on my research, I have found certain values for these settings that make a lot of sense.
Dot Density Debate
There's been a lot of debate on internet forums over the years on whether prints have enough detail to bother scanning them above 300dpi. Many people say there is not, yet others have posted image comparisons showing more detail in 600dpi scans. Because of these unresolved debates, I decided to perform my own dpi tests. I strived for conclusive results so that I can make informed suggestions to others.
For all the photos below, I made three scans at the three most mentioned dpi settings (300, 400, 600) on an Epson Perfection V600 Photo scanner. The scans were made at the second exposure setting and were not color corrected or enhanced in any way. I cropped an identical area from each scan. I then enlarged each crop by a certain percentage using the nearest neighbor algorithm to preserve hard edges. This makes it vastly easier to see each individual scanned pixel.
The percentages I used for enlarging were 1200% for the 90x90 300dpi crops, 900% for the 120x120 400dpi crops, and 600% for the 180x180 600dpi crops. Varying the percentages according to the dpi resulted in images of equal size for ease of comparison. Using such large percentages, along with the nearest neighbor algorithm, greatly minimizes the automatic smoothing that happens when images are viewed on a web page. If this enlargement is not done, the automatic smoothing will make it impossible to see the original scanned pixels.
3x5 35mm Print
Here's a closeup of a 35mm print of a Christmas tree taken by a compact camera with a built-in lens. The sharpness and quality are very typical of the other 35mm prints in my collection. I selected it because all of the tiny needles would be a good demonstration of how much detail prints can hold.
As you can see, the 300dpi image is very pixelated. The needles are very jagged, the lights are blocky, and the silver tinsel on the right is a mess.
The 400dpi image is significantly better. The strands of silver tinsel are more separated and the ring at the top of the ball is easier to identify. However, the image is still noticeably pixelated, especially the light-colored twigs, silver top of the ball, and lights. At this dpi, noise starts to become noticeable, an unfortunate side effect of higher dpi.
The 600dpi image looks quite nice. Pixelation is not very apparent at all. The silver strands of tinsel are clearly separated from each other and have refined edges. The needles look like real needles now. The ring at the top of the ball looks better. The bright parts of the twigs are very smooth. This image is an excellent representation of the details on the print.
The 300dpi and 600dpi images are like night and day.
I wanted to take a look at instant prints next, as they tend to have a reputation for being blurry. The Polaroids in my family album are no exception, including the Polaroid I selected to test. I selected it because it has a pattern in the fabric that would be a good test subject.
Not surprisingly, the pattern is very soft with no fine details. There is very light pixelation along the edges of bright areas in the 300dpi scan. These areas are slightly improved in the 400dpi scan. The 600dpi scan looks about the same as the 400dpi scan.
Because the image has such soft edges, scanning at 400dpi or 300dpi should be good enough.
Polacolor Peel-Apart Print
Another kind of instant print in my collection is the Polacolor peel-apart print. The print is peeled away from the negative after taking a photo and waiting for about a minute or so. These Polacolor prints look less like traditional Polaroids with the wide bottom borders, and more like regular prints. They seem to hold more detail than traditional Polaroids as well.
As the Polacolor prints seem to contain more detail than a traditional Polaroids, I thought they would make for a good third test subject. I selected a Polacolor print containing an area with good edges and decent detail.
Edges with high contrast have a lot of rough pixelation in the 300dpi scan. The text on the can are completely pixelated.
Pixelation is greatly reduced but still apparent in the 400dpi scan.
The 600dpi scan has very refined edges, even including the high contrast edges. The text on the can and envelope look as good as on the original photo.
4x6 35mm Print
Most of my collection contains 35mm prints, so I wanted to perform a final test on a 4x6 35mm print with small identifiable details. I selected a photo of a city taken from a hilltop. The cropped area has a bridge, buildings, and vegetation.
The 300dpi scan has pixelation along edges of bright objects, such as buildings and the bridge. The bridge has especially strong pixelation on the bridge supports and light posts.
Pixelation has improved in the 400dpi scan but is still noticeable on the bridge supports and light posts. There appears to be more details in the vegetation.
The bridge supports and light posts in the 600dpi scan are refined and free of most pixelation. The 600dpi scan has captured all the detail in the photo.
|shown with a width of 180, normal size for 600dpi
the beast, 300dpi
To capture all of the available detail in a print, it is necessary to scan at 600dpi. Scanning with lower dpi values can cause pixelation and loss of fine detail. Even some instant prints benefit from 600dpi scans.
|shown with a width of 90|
normal size for 300dpi
Traditional Polaroids with the wide bottom borders may be an exception. They can probably be scanned at 400dpi or 300dpi without noticeable detail loss.
Which do you choose? :)
Suggested Settings Summary
DPI for Prints: Based on the above test results, it is necessary to scan photos at 600dpi to capture all details and prevent pixelation (although blurry Polaroids can be scanned at 300dpi).
DPI for Film (slides & negatives): Should be between 3000dpi and 4000dpi for all formats (35mm, APS, Medium Format, and Large Format) according to the general consensus on the web. ScanDig, a company that does extensive lab tests of scanners, states 2000dpi as unsuitable for archiving 35mm film, while 4000dpi is recommended for film taken with top quality cameras and lenses. ScanYourEntireLife recommends a dpi between 3000 and 4000 for scanning film. Many large scanning services offer 3000dpi as standard and 4000dpi as a pro or premium option.
- Enlargements: Enlarging a scanned image with an image editor can result in pixelation. To avoid this, the image can be enlarged by scanning it at an increased dpi. Doubling the size of a photo requires double the dpi (2x600), tripling the size requires triple the dpi, and so forth.
- Small prints: Small prints (2x3 and smaller) often need to be larger, either for viewing on a screen or making prints. The best way to enlarge small prints is to scan them at 1200dpi which will double the image size.
- Large prints: Scanning large full-page prints creates large files. If your 8x10s are blurry and you need to save hard disk space, you can scan them at 300dpi. Otherwise, 600dpi is a better choice.
Color Depth: A 48-bit color image uses 65,536 shades of color for each channel. A 24-bit color image only uses 256 shades of color for each channel. Because of the limited shades of color in 24-bit color images, making major edits to the image can cause posterization damage as explained in the Color Depth section of the Info page. I therefore suggest making 48-bit color scans of color and grayscale photos. If you wish to make grayscale scans, I suggest 16-bit grayscale scans.
- 4000dpi: Archive quality scans for film taken with top quality cameras. Best scanned with high quality film scanners.
- 3000dpi: Popular choice for high quality scans. Equivalent to 10 megapixel digital camera images.
- 2000dpi to 1000dpi: Useful for Large Format film to avoid massively huge files that 4000dpi scans would generate.
Color/Grayscale: I recommend selecting Color for both color and grayscale photos. While you can select Grayscale for grayscale (aka black & white) photos, please note the following.
Image Format: This may also be referred to as data format or image type. Scan software supports saving the scanned image as tiffs or jpegs. See below for information about each type of image.
- ScanGear. Canon ScanGear cannot make 16-bit grayscale scans. Instead of making 8-bit grayscale scans, I suggest making 48-bit color scans of all your photos.
- Stains. If you have a grayscale photo that has a colored stain on it (such as blue ink), it may be easier to remove that stain later if you make a color scan of the photo.
- Simplicity. It is simpler to standardize on Color for both color and grayscale photos, rather than switching between Color and Grayscale.
- Standards. Unprofiled color images are treated as being in the standard sRGB color space by most modern computer systems. Unprofiled grayscale images have no default color space in comparison. If a profiled grayscale image loses its profile, results may be unpredictable. See the Default Color Space paragraphs under Color Standards for more info.
- Tiffs: Tiffs can handle 16-bit grayscale and 48-bit color images. Also, there is never a loss of quality when editing and re-saving tiffs. This makes tiffs perfect for photo restoration. If you plan to archive or restore your scans, I suggest selecting uncompressed tiffs as the image format.
- Jpegs: Image quality is lost every time a jpeg is edited and re-saved. Also, jpegs have an 24-bit color depth and won't be able to save scans made at a 48-bit color depth. If space is an issue and you plan to never edit or color correct your scans, jpegs may be okay.
- are typically very large files
- retain all image quality when compressed with LZW or ZIP
- support up to 48 bit color images
- are widely supported by graphics programs
- are rarely supported by web browsers
TIFFs are often used for scanning, editing, printing, or archiving high quality images. EU's Succeed report on formats recommends TIFFs (uncompressed or LZW compression) for the preservation of still images. |
To retain all image quality, TIFFs normally use no compression or LZW or ZIP lossless compression. JPEG lossy compression is rarely used for obvious reasons. LZW is commonly used and works well with 24-bit images, but works poorly with 48-bit images. ZIP is slightly better at compressing images, but is
newer and less commonly supported. Both LZW and ZIP compression greatly increase the save time for 24-bit images.
Pixel Order is a TIFF option set to Interleaved or Per Channel (aka Planar). Interleaved is the normal arrangement of pixels from first to last, with each pixel having a red value, green value, and blue value in that order (RGBRGBRGB). Per Channel rearranges the pixels by color channel, starting with all of the red values of all the pixels, followed by all the green values, and ending with all the blue values (RRRGGGBBB). Supposedly, Per Channel helps a little with compression, but is not widely supported.
Byte Order is a TIFF option designed to support the Endianness of the target CPU, either Intel (PC) or Motorola (Mac). Not only should this option be obselete (as both PC and Mac computers use Intel CPUs now), but virtually all modern programs support either Byte Order on any type of computer.
- are typically small files
- lose some image quality when compressed
- degrades in image quality for each edit and re-save
- only support 24-bit color images
- are widely supported by graphics programs
- are widely supported by web browsers
JPEG is a popular format for photographic images on the web because of their small size. To achieve such a small file size, JPEG files use lossy compression. The degree of compression is selectable anywhere in a broad range from low to high. |
A low degree of compression results in a small file size and virtually no noticeable change to image quality. A high degree of results in a much smaller file size and significant loss in image quality. Quality is lost because some image details are permanently discarded to save space. Even more quality is lost due to generation loss, which occurs every time the image is opened, edited, and re-saved.