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Scanning resolution, printing resolution, and downsampling
I just read Margulis' chapter on resolution and am somewhat confused
(it's one of those things you have to read multiple times, I think). Up to now I have been scanning my 6x6 and some 35mm slides and negs at 3000-4000dpi on a Nikon LS8000 at 14-bit depth, and manipulating mostly at full res, then downsampling to 300dpi before sending it to my Epson 2200. According to Margulis, having a resolution too high can soften an image, so I'm trying to find out two things: 1. Is the softening that occurs an effect of sending too much data to the printer, and if so, wouldn't downsampling before printing correct it, or should it be scanned at a lower resolution to begin with? 2. Where can I find a reference of starting points for optimum scanning resolution that considers input film size, final print size, and optimum print resolution? Thanks for any input. Chris |
#2
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"hassy_user" wrote in message om... I just read Margulis' chapter on resolution and am somewhat confused (it's one of those things you have to read multiple times, I think). Up to now I have been scanning my 6x6 and some 35mm slides and negs at 3000-4000dpi on a Nikon LS8000 at 14-bit depth, and manipulating mostly at full res, So far, you've done well. then downsampling to 300dpi before sending it to my Epson 2200. That is not optimal. The 2200 (like most desktop Epsons) internally dithers based on a 720ppi image. If the ppi for the output size requested is different, the printer driver will interpolate to 720 ppi. In your case, it will more than quadruple the number of pixels you offered it. Interpolation will not help resolution. According to Margulis, having a resolution too high can soften an image, so I'm trying to find out two things: 1. Is the softening that occurs an effect of sending too much data to the printer, and if so, wouldn't downsampling before printing correct it, or should it be scanned at a lower resolution to begin with? As stated above, only down-sample to 720 ppi at output size. Then sharpen the result, you can visually oversharpen a bit, because there will be losses in the printing process. Always judge the amount of sharpening at 100% zoom level in the photoeditor. 2. Where can I find a reference of starting points for optimum scanning resolution that considers input film size, final print size, and optimum print resolution? Scanning film at the highest native resolution will reduce apparent graininess, so by all means keep doing it as you are. You can improve the downsampling quality by applying a little blur before downsampling. The amount of blur needed depends on the amount of downsampling. That will also help reducing apparent graininess, instead of increasing it due to grain-aliasing. http://www.xs4all.nl/~bvdwolf/main/f...own_sample.htm http://www.xs4all.nl/~bvdwolf/main/f...e/example1.htm Print resolution, as stated should in your case be 720 ppi after resampling. Grain aliasing is explained he http://www.photoscientia.co.uk/Grain.htm Bart |
#3
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"hassy_user" wrote in message om... I just read Margulis' chapter on resolution and am somewhat confused (it's one of those things you have to read multiple times, I think). Up to now I have been scanning my 6x6 and some 35mm slides and negs at 3000-4000dpi on a Nikon LS8000 at 14-bit depth, and manipulating mostly at full res, So far, you've done well. then downsampling to 300dpi before sending it to my Epson 2200. That is not optimal. The 2200 (like most desktop Epsons) internally dithers based on a 720ppi image. If the ppi for the output size requested is different, the printer driver will interpolate to 720 ppi. In your case, it will more than quadruple the number of pixels you offered it. Interpolation will not help resolution. According to Margulis, having a resolution too high can soften an image, so I'm trying to find out two things: 1. Is the softening that occurs an effect of sending too much data to the printer, and if so, wouldn't downsampling before printing correct it, or should it be scanned at a lower resolution to begin with? As stated above, only down-sample to 720 ppi at output size. Then sharpen the result, you can visually oversharpen a bit, because there will be losses in the printing process. Always judge the amount of sharpening at 100% zoom level in the photoeditor. 2. Where can I find a reference of starting points for optimum scanning resolution that considers input film size, final print size, and optimum print resolution? Scanning film at the highest native resolution will reduce apparent graininess, so by all means keep doing it as you are. You can improve the downsampling quality by applying a little blur before downsampling. The amount of blur needed depends on the amount of downsampling. That will also help reducing apparent graininess, instead of increasing it due to grain-aliasing. http://www.xs4all.nl/~bvdwolf/main/f...own_sample.htm http://www.xs4all.nl/~bvdwolf/main/f...e/example1.htm Print resolution, as stated should in your case be 720 ppi after resampling. Grain aliasing is explained he http://www.photoscientia.co.uk/Grain.htm Bart |
#4
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From: (hassy_user)
I just read Margulis' chapter on resolution and am somewhat confused Up to now I have been scanning my 6x6 and some 35mm slides and negs at 3000-4000dpi on a Nikon LS8000 at 14-bit depth, and manipulating mostly at full res, then downsampling to 300dpi before sending it to my Epson 2200. According to Margulis, having a resolution too high can soften an image, so I'm trying to find out two things: 1. Is the softening that occurs an effect of sending too much data to the printer, and if so, wouldn't downsampling before printing correct it, or should it be scanned at a lower resolution to begin with? Dan is a member of the "scan for the target output" club, which is the way most book and magazine publishers and many advertising agencies work. They rarely print large prints (especially magazines and books) and don't spend a lot of time fine-tuning each image, as a general rule. The other side of the coin is the "scan once, output many" club which feels it's best to scan at high rez, do all your prep work on a master file (which is what you're doing) and downsample and sharpen to various output sizes ranging from large fine art prints to tiny web thumbnails. Here's a good explanation of the theory from a fine art lab I've used, West Coast Imaging ... http://www.westcoastimaging.com/wci/.../scanonce.html The key to doing this well is to know how to downsample well and how to use USM in a variety of situations, typically with film using edge sharpening or something similar. You should be able to run a test yourself with the 8000 and see if downsampling works for you ... just scan at the native rez (4,000 dpi) and downsample to say 360 ppi for a decent sized print and print it. Also scan at the exact rez for this size print and print directly from that one too without downsampling ... if you're printing 10x10" @ 360 ppi for example you need 3600 pixels/side so would scan at roughly 1650 dpi (the Nikon software lets you set this exactly). See what looks best, the 10x10" print at 1650 or the 4000 dpi scan downsampled. Keep in mind Dan has access to much better scanners than your 8000 (which is what I use too and he may get a better result with his 1650 dpi scan than you or I with the Nikon. The Nikon will still scan internally at 4,000 dpi and then downsample with its software ... can you do this better in Photoshop yourself? 2. Where can I find a reference of starting points for optimum scanning resolution that considers input film size, final print size, and optimum print resolution? You can work backwards once you know the optimal printer ppi and the desired print size (multiply the ppi x the print dimensions to get the pixel count and divide this by the size of the film to get the scan rez), but of course the main problem is that you'll get a different target scan rez for each print size and for each printer ppi. No problem if you're scanning once for a magazine article but a hassle if you think you'll print the same file yourself at various sizes or need even smaller images for the web. If you want to see what a real digital ace can do with the "scan once and resize" flow look at Bill Atkinson's work. He shoots Velvia with a Hassy and scans at 5,000 dpi with a Tango drum, then resizes these files for anything from a 24x24" fine art print at 360 ppi to thumbnails for the web that are 100x100 pixels ... http://www.billatkinson.com/CatalogIndex.html Bill |
#5
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From: (hassy_user)
I just read Margulis' chapter on resolution and am somewhat confused Up to now I have been scanning my 6x6 and some 35mm slides and negs at 3000-4000dpi on a Nikon LS8000 at 14-bit depth, and manipulating mostly at full res, then downsampling to 300dpi before sending it to my Epson 2200. According to Margulis, having a resolution too high can soften an image, so I'm trying to find out two things: 1. Is the softening that occurs an effect of sending too much data to the printer, and if so, wouldn't downsampling before printing correct it, or should it be scanned at a lower resolution to begin with? Dan is a member of the "scan for the target output" club, which is the way most book and magazine publishers and many advertising agencies work. They rarely print large prints (especially magazines and books) and don't spend a lot of time fine-tuning each image, as a general rule. The other side of the coin is the "scan once, output many" club which feels it's best to scan at high rez, do all your prep work on a master file (which is what you're doing) and downsample and sharpen to various output sizes ranging from large fine art prints to tiny web thumbnails. Here's a good explanation of the theory from a fine art lab I've used, West Coast Imaging ... http://www.westcoastimaging.com/wci/.../scanonce.html The key to doing this well is to know how to downsample well and how to use USM in a variety of situations, typically with film using edge sharpening or something similar. You should be able to run a test yourself with the 8000 and see if downsampling works for you ... just scan at the native rez (4,000 dpi) and downsample to say 360 ppi for a decent sized print and print it. Also scan at the exact rez for this size print and print directly from that one too without downsampling ... if you're printing 10x10" @ 360 ppi for example you need 3600 pixels/side so would scan at roughly 1650 dpi (the Nikon software lets you set this exactly). See what looks best, the 10x10" print at 1650 or the 4000 dpi scan downsampled. Keep in mind Dan has access to much better scanners than your 8000 (which is what I use too and he may get a better result with his 1650 dpi scan than you or I with the Nikon. The Nikon will still scan internally at 4,000 dpi and then downsample with its software ... can you do this better in Photoshop yourself? 2. Where can I find a reference of starting points for optimum scanning resolution that considers input film size, final print size, and optimum print resolution? You can work backwards once you know the optimal printer ppi and the desired print size (multiply the ppi x the print dimensions to get the pixel count and divide this by the size of the film to get the scan rez), but of course the main problem is that you'll get a different target scan rez for each print size and for each printer ppi. No problem if you're scanning once for a magazine article but a hassle if you think you'll print the same file yourself at various sizes or need even smaller images for the web. If you want to see what a real digital ace can do with the "scan once and resize" flow look at Bill Atkinson's work. He shoots Velvia with a Hassy and scans at 5,000 dpi with a Tango drum, then resizes these files for anything from a 24x24" fine art print at 360 ppi to thumbnails for the web that are 100x100 pixels ... http://www.billatkinson.com/CatalogIndex.html Bill |
#6
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Bill Hilton wrote: Hi... much snipped You should be able to run a test yourself with the 8000 and see if downsampling works for you ... just scan at the native rez (4,000 dpi) and downsample to say 360 ppi for a decent sized print and print it. Also scan at the exact rez for this size print and print directly from that one too without downsampling ... if you're printing 10x10" @ 360 ppi for example you need 3600 pixels/side so would scan at roughly 1650 dpi (the Nikon software lets you set this exactly). more snipped For what it's worth, I did this test using many variations... about 20 prints worth. (Kodak machine in the mall type prints) Blind tests for which was better was always extremely close. Testers (included print machine operator, the subject herself, neighbors and friends) after long consideration always concluded that the "big" scan, untouched by PS or PSP, was the best. Ken |
#7
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Bill Hilton wrote: Hi... much snipped You should be able to run a test yourself with the 8000 and see if downsampling works for you ... just scan at the native rez (4,000 dpi) and downsample to say 360 ppi for a decent sized print and print it. Also scan at the exact rez for this size print and print directly from that one too without downsampling ... if you're printing 10x10" @ 360 ppi for example you need 3600 pixels/side so would scan at roughly 1650 dpi (the Nikon software lets you set this exactly). more snipped For what it's worth, I did this test using many variations... about 20 prints worth. (Kodak machine in the mall type prints) Blind tests for which was better was always extremely close. Testers (included print machine operator, the subject herself, neighbors and friends) after long consideration always concluded that the "big" scan, untouched by PS or PSP, was the best. Ken |
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#9
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#10
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"hassy_user" wrote in message om... SNIP Bill and Bart, you apparently differ on the recommended output ppi (360 vs 720). Will there be a visible difference, however subtle, in choosing one over the other? Depends on the image processing done to the final sized file, and whether it had enough resolution to begin with. Assuming the file has enough native resolution, the 720 ppi version will allow to enhance edge contrast more accurately. The resulting output will look better in that case. If you use a dedicated print program like Qimage, life becomes even easier because it takes care of it automagically (including profile conversion and optimization of paper used), without altering the original file. Bart |
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