{"course":{"slug":"image-editing","title":"Editing an Image","url":"https://addaly.com/learn/image-editing","level":"beginner","track":"create"},"lesson":{"slug":"scanning-a-print","title":"Getting the photograph off the paper","url":"https://addaly.com/learn/image-editing/scanning-a-print","position":47,"of":78,"minutes":9,"answer":"Scan resolution is chosen from the intended output size with room for correction, moiré from a previously printed original is an interference pattern best removed by oversampling and downscaling.","keyIdea":"Scan resolution is chosen from the intended output size with room for correction, moiré from a previously printed original is an interference pattern best removed by oversampling and downscaling, and infrared dust removal fails on silver black-and-white and Kodachrome because the image itself blocks infrared."},"body":{"format":"markdown","text":"## Resolution: scan for the output, with room\n\nA flatbed scanner's dpi setting is real, unlike a JPEG's ppi tag: it determines how many samples are taken per inch of the original.\n\nThe arithmetic you need:\n\n- **A 6×4 inch print reprinted at the same size** needs 300 dpi minimum. Scan at **600** so you have room to crop, straighten and correct.\n- **A 6×4 print to be enlarged to A4**: that is roughly a 2.5× enlargement, so scan at **800 to 1200 dpi**.\n- **A 35 mm negative or slide** is about one inch across, so a usable file needs **2400 to 4000 dpi**, and that requires a scanner with a transparency unit. A flatbed's stated 9600 dpi is usually interpolated marketing rather than real optical resolution; look for the *optical* figure.\n- **Above the scanner's optical resolution there is no gain**, only file size. The sensor cannot sample more finely than it can sample.\n\nScan in **16-bit** if the option exists. An old print is often faded and low in contrast, which means the correction will be a heavy stretch, which is exactly the case for extra bit depth.\n\nSave the raw scan as a **TIFF** and never overwrite it. That file is the closest thing to the original that will exist once the print fades further.\n\n## Moiré, and the print that was already printed\n\nScanning a photographic print from a lab is straightforward. Scanning something from a **magazine, newspaper or book** is not, because that image is made of a regular grid of halftone dots.\n\nWhen the scanner's sampling grid meets the printing screen's grid, the two interfere and you get **moiré**: coloured wave patterns across the image. This is the same aliasing mechanism as the demosaic moiré from the first module, and it is not a fault.\n\nThree fixes, in order of quality:\n\n1. **Scan at a much higher resolution than you need, then downsample.** Scanning at 1200 dpi and reducing to 300 averages many samples per printed dot, which removes the interference properly. This is the best result and the largest files.\n2. **Use the scanner software's descreen setting**, naming the original type (newspaper, magazine, book). It applies a targeted blur. Fast, and it costs sharpness.\n3. **Rotate the original a few degrees on the glass**, scan, and rotate back in software. Changing the angle between the two grids breaks the interference pattern. Crude, effective, free.\n\nIn the editor, a small Gaussian blur followed by sharpening also suppresses residual moiré, and a **Median** filter at 1 to 2 pixels is often better than a blur because it removes the dot pattern while keeping edges.\n\n## Dust and scratches\n\n**Clean the glass and the print** before anything else. A microfibre cloth and, for the print, a soft brush. Two minutes here saves an hour of healing.\n\n**Infrared dust removal** (sold as Digital ICE, FARE, or similar) uses a fourth infrared channel to detect physical defects, because dust and scratches block infrared while the image dyes do not. It is excellent and it has two exceptions that catch everybody: it does **not** work on traditional silver black-and-white negatives, or on Kodachrome, because in both the image itself is opaque to infrared and gets detected as damage. Turning it on for those produces a smeared mess.\n\nFor prints, infrared removal generally does not apply: it is a film-scanning feature. Prints are cleaned by hand in the editor.\n\n## Flatness, and photographing instead\n\nA curled print will not sit on the glass and scans with a soft band. Put it under a heavy book overnight, or scan with the lid pressed down and a weight on top.\n\nNo scanner? A phone works, and the technique matters:\n\n- **Even light, no direct source.** Two lamps at 45 degrees from opposite sides, or an overcast window, or outdoors in open shade. A single overhead light produces a glare patch.\n- **Camera square to the print.** Tilt introduces keystone which then has to be corrected, and correcting it resamples.\n- **Avoid the phone's own shadow**, which is why the light comes from the sides.\n- **Use the main camera, not the ultrawide**, whose distortion bends the print's edges.\n- **Shoot DNG if you can**, for the bit depth on a faded original.\n- Crop and correct perspective afterwards. Most phone galleries and Adobe Scan do this automatically, and doing it manually with a perspective transform gives a better result.\n\nA phone photograph in good light beats a bad scan, and both beat a photograph taken at an angle under a ceiling light.\n\n## Free software for scanning\n\n**XSane** and **Simple Scan** on Linux, **NAPS2** on Windows, and **VueScan** across platforms (paid, and it supports very old scanners whose manufacturers abandoned drivers years ago, which is often the only thing that will).\n\n**GIMP** can drive a scanner directly through XSane. For negatives, **darktable** has a *negadoctor* module that inverts and corrects colour negative film scans properly, accounting for the orange mask: this is a hard job done well, and free.\n\n## What the scan cannot recover\n\nA scan captures what is on the paper now. If the print has faded, the scan captures the faded version; if it has yellowed, the scan captures the yellow.\n\nSome of that is correctable, which is the next lesson. Some is not: where a dye has faded to nothing, there is no residual signal to amplify, and lifting that area produces noise and paper texture rather than a picture. A print left in a window for thirty years may have a corner with no image left.\n\nAnd resolution cannot exceed what the print holds. A small print from a 1970s compact camera on cheap paper may contain very little detail; scanning it at 2400 dpi produces a large file of magnified paper grain. Scan it at 600, and spend the time on the tonal restoration instead."},"check":{"question":"An archivist scans a photograph from an old magazine at exactly 300 dpi for a 300 dpi reprint, and the result shows coloured wave patterns across the image. What is the best fix?","options":[{"text":"Enable infrared dust removal, which detects the printing screen as a surface defect and removes it.","correct":false,"tempting":"Misapplies a defect-detection channel: infrared identifies physical dust and scratches, and printed halftone dots are part of the image and fully visible to it."},{"text":"Scan at 1200 dpi and downsample to 300, so many samples average across each printed dot and the interference disappears.","correct":true},{"text":"Scan at 150 dpi to sample below the printing screen's frequency, then upscale to 300.","correct":false,"tempting":"Moves in the wrong direction: sampling more coarsely than the dot grid worsens aliasing and discards real image detail that upscaling cannot restore."},{"text":"Increase the scanner's colour depth to 16-bit, which gives enough levels to represent the dot pattern smoothly.","correct":false,"tempting":"Adds precision to a spatial sampling problem: the waves come from grid interference and appear identically at any bit depth."}]},"prev":{"slug":"liquify-warp-and-the-line","title":"Moving pixels, and the straight line that gives it away","url":"https://addaly.com/learn/image-editing/liquify-warp-and-the-line"},"next":{"slug":"restoring-a-damaged-photograph","title":"Tears, mould and the cyan that faded first","url":"https://addaly.com/learn/image-editing/restoring-a-damaged-photograph"},"authorship":"Founder and series editor: Dr Mustafa Mun. Written by AI models to a written standard. Exam keys checked blind by a second model: 3,665 of 3,666 agreed. Academic review invited.","review":{"status":"Draft, open for academic review"},"cite":"Addaly (2026) 'Getting the photograph off the paper', in Editing an Image. Edited by M. Mun. Addaly. Available at: https://addaly.com/learn/image-editing/scanning-a-print (Accessed: 13 October 2026).","licence":{"name":"CC BY-NC-SA 4.0","url":"https://creativecommons.org/licenses/by-nc-sa/4.0/"},"reader":{"schema":1,"title":"Getting the photograph off the paper","courseTitle":"Editing an Image","module":{"index":5,"slug":"repair-and-retouching","title":"Repair and retouching"},"answer":null,"keyIdea":"Scan resolution is chosen from the intended output size with room for correction, moiré from a previously printed original is an interference pattern best removed by oversampling and downscaling, and infrared dust removal fails on silver black-and-white and Kodachrome because the image itself blocks infrared.","hero":{"kind":"plate","image":null,"alt":null,"caption":null},"blocks":[{"t":"h2","id":"resolution-scan-for-the-output-with-room","runs":[{"text":"Resolution: scan for the output, with room"}]},{"t":"p","runs":[{"text":"A flatbed scanner’s dpi setting is real, unlike a JPEG’s ppi tag: it determines how many samples are taken per inch of the original."}]},{"t":"p","runs":[{"text":"The arithmetic you need:"}]},{"t":"ul","items":[[{"text":"A 6×4 inch print reprinted at the same size","b":true},{"text":" needs 300 dpi minimum. Scan at "},{"text":"600","b":true},{"text":" so you have room to crop, straighten and correct."}],[{"text":"A 6×4 print to be enlarged to A4","b":true},{"text":": that is roughly a 2.5× enlargement, so scan at "},{"text":"800 to 1200 dpi","b":true},{"text":"."}],[{"text":"A 35 mm negative or slide","b":true},{"text":" is about one inch across, so a usable file needs "},{"text":"2400 to 4000 dpi","b":true},{"text":", and that requires a scanner with a transparency unit. A flatbed’s stated 9600 dpi is usually interpolated marketing rather than real optical resolution; look for the "},{"text":"optical","i":true},{"text":" figure."}],[{"text":"Above the scanner’s optical resolution there is no gain","b":true},{"text":", only file size. The sensor cannot sample more finely than it can sample."}]]},{"t":"p","runs":[{"text":"Scan in "},{"text":"16-bit","b":true},{"text":" if the option exists. An old print is often faded and low in contrast, which means the correction will be a heavy stretch, which is exactly the case for extra bit depth."}]},{"t":"p","runs":[{"text":"Save the raw scan as a "},{"text":"TIFF","b":true},{"text":" and never overwrite it. That file is the closest thing to the original that will exist once the print fades further."}]},{"t":"h2","id":"moir-and-the-print-that-was-already-printed","runs":[{"text":"Moiré, and the print that was already printed"}]},{"t":"p","runs":[{"text":"Scanning a photographic print from a lab is straightforward. Scanning something from a "},{"text":"magazine, newspaper or book","b":true},{"text":" is not, because that image is made of a regular grid of halftone dots."}]},{"t":"p","runs":[{"text":"When the scanner’s sampling grid meets the printing screen’s grid, the two interfere and you get "},{"text":"moiré","b":true},{"text":": coloured wave patterns across the image. This is the same aliasing mechanism as the demosaic moiré from the first module, and it is not a fault."}]},{"t":"p","runs":[{"text":"Three fixes, in order of quality:"}]},{"t":"ol","start":1,"items":[[{"text":"Scan at a much higher resolution than you need, then downsample.","b":true},{"text":" Scanning at 1200 dpi and reducing to 300 averages many samples per printed dot, which removes the interference properly. This is the best result and the largest files."}],[{"text":"Use the scanner software’s descreen setting","b":true},{"text":", naming the original type (newspaper, magazine, book). It applies a targeted blur. Fast, and it costs sharpness."}],[{"text":"Rotate the original a few degrees on the glass","b":true},{"text":", scan, and rotate back in software. Changing the angle between the two grids breaks the interference pattern. Crude, effective, free."}]]},{"t":"p","runs":[{"text":"In the editor, a small Gaussian blur followed by sharpening also suppresses residual moiré, and a "},{"text":"Median","b":true},{"text":" filter at 1 to 2 pixels is often better than a blur because it removes the dot pattern while keeping edges."}]},{"t":"h2","id":"dust-and-scratches","runs":[{"text":"Dust and scratches"}]},{"t":"p","runs":[{"text":"Clean the glass and the print","b":true},{"text":" before anything else. A microfibre cloth and, for the print, a soft brush. Two minutes here saves an hour of healing."}]},{"t":"p","runs":[{"text":"Infrared dust removal","b":true},{"text":" (sold as Digital ICE, FARE, or similar) uses a fourth infrared channel to detect physical defects, because dust and scratches block infrared while the image dyes do not. It is excellent and it has two exceptions that catch everybody: it does "},{"text":"not","b":true},{"text":" work on traditional silver black-and-white negatives, or on Kodachrome, because in both the image itself is opaque to infrared and gets detected as damage. Turning it on for those produces a smeared mess."}]},{"t":"p","runs":[{"text":"For prints, infrared removal generally does not apply: it is a film-scanning feature. Prints are cleaned by hand in the editor."}]},{"t":"h2","id":"flatness-and-photographing-instead","runs":[{"text":"Flatness, and photographing instead"}]},{"t":"p","runs":[{"text":"A curled print will not sit on the glass and scans with a soft band. Put it under a heavy book overnight, or scan with the lid pressed down and a weight on top."}]},{"t":"p","runs":[{"text":"No scanner? A phone works, and the technique matters:"}]},{"t":"ul","items":[[{"text":"Even light, no direct source.","b":true},{"text":" Two lamps at 45 degrees from opposite sides, or an overcast window, or outdoors in open shade. A single overhead light produces a glare patch."}],[{"text":"Camera square to the print.","b":true},{"text":" Tilt introduces keystone which then has to be corrected, and correcting it resamples."}],[{"text":"Avoid the phone’s own shadow","b":true},{"text":", which is why the light comes from the sides."}],[{"text":"Use the main camera, not the ultrawide","b":true},{"text":", whose distortion bends the print’s edges."}],[{"text":"Shoot DNG if you can","b":true},{"text":", for the bit depth on a faded original."}],[{"text":"Crop and correct perspective afterwards. Most phone galleries and Adobe Scan do this automatically, and doing it manually with a perspective transform gives a better result."}]]},{"t":"p","runs":[{"text":"A phone photograph in good light beats a bad scan, and both beat a photograph taken at an angle under a ceiling light."}]},{"t":"h2","id":"free-software-for-scanning","runs":[{"text":"Free software for scanning"}]},{"t":"p","runs":[{"text":"XSane","b":true},{"text":" and "},{"text":"Simple Scan","b":true},{"text":" on Linux, "},{"text":"NAPS2","b":true},{"text":" on Windows, and "},{"text":"VueScan","b":true},{"text":" across platforms (paid, and it supports very old scanners whose manufacturers abandoned drivers years ago, which is often the only thing that will)."}]},{"t":"p","runs":[{"text":"GIMP","b":true},{"text":" can drive a scanner directly through XSane. For negatives, "},{"text":"darktable","b":true},{"text":" has a "},{"text":"negadoctor","i":true},{"text":" module that inverts and corrects colour negative film scans properly, accounting for the orange mask: this is a hard job done well, and free."}]},{"t":"h2","id":"what-the-scan-cannot-recover","runs":[{"text":"What the scan cannot recover"}]},{"t":"p","runs":[{"text":"A scan captures what is on the paper now. If the print has faded, the scan captures the faded version; if it has yellowed, the scan captures the yellow."}]},{"t":"p","runs":[{"text":"Some of that is correctable, which is the next lesson. Some is not: where a dye has faded to nothing, there is no residual signal to amplify, and lifting that area produces noise and paper texture rather than a picture. A print left in a window for thirty years may have a corner with no image left."}]},{"t":"p","runs":[{"text":"And resolution cannot exceed what the print holds. A small print from a 1970s compact camera on cheap paper may contain very little detail; scanning it at 2400 dpi produces a large file of magnified paper grain. Scan it at 600, and spend the time on the tonal restoration instead."}]}],"check":{"question":[{"text":"An archivist scans a photograph from an old magazine at exactly 300 dpi for a 300 dpi reprint, and the result shows coloured wave patterns across the image. What is the best fix?"}],"options":[{"text":[{"text":"Enable infrared dust removal, which detects the printing screen as a surface defect and removes it."}],"correct":false,"tempting":[{"text":"Misapplies a defect-detection channel: infrared identifies physical dust and scratches, and printed halftone dots are part of the image and fully visible to it."}]},{"text":[{"text":"Scan at 1200 dpi and downsample to 300, so many samples average across each printed dot and the interference disappears."}],"correct":true,"tempting":null},{"text":[{"text":"Scan at 150 dpi to sample below the printing screen’s frequency, then upscale to 300."}],"correct":false,"tempting":[{"text":"Moves in the wrong direction: sampling more coarsely than the dot grid worsens aliasing and discards real image detail that upscaling cannot restore."}]},{"text":[{"text":"Increase the scanner’s colour depth to 16-bit, which gives enough levels to represent the dot pattern smoothly."}],"correct":false,"tempting":[{"text":"Adds precision to a spatial sampling problem: the waves come from grid interference and appear identically at any bit depth."}]}],"order":[2,3,0,1],"why":null},"prev":{"slug":"liquify-warp-and-the-line","title":"Moving pixels, and the straight line that gives it away","minutes":9},"next":{"slug":"restoring-a-damaged-photograph","title":"Tears, mould and the cyan that faded first","minutes":9}}}