Scanning prints, negatives, and slides
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This image file was generated from a 35mm slide via a transparent media scan using the Agfa Arcus-II scanner and its transparency adapter. There are two flavors of the original image as placed in the scanner. All 35a files were scanned with a transparency mounted in the Agfa transparency image frame which comes with the scanner. The 35b files were scanned with a standard mounted 35mm transparency. Both forms of transparencies were laid flat, face down, on the scanner glass. In addition to the two forms of media mounting, each form was scanned at four different resolutions into uncompressed TIF output files. Output file size was not constrained. The resulting scan data is:
In this example, output file size grows larger as the input scan resolution is increased. This is due to the output image size being automatically increased. The following files are available via this Web page:
| 35a-200.tif | 35a-200.jpg | 35a-400.jpg | 35a-600.jpg | 35a-800.jpg | These files were generated using LViewPro32. Before saving, the gamma was adjusted by +30 and the output image size was changed to be the same as the 200 lpi file (436x291). Conclusion The results of this scanning exercise suggests that high quality flatbed scanners can produce satisfactory output for prepress and Web use. Nuts & Bolts of Scanning The discussion thus far demonstrated how a flatbed scanner can produce acceptable images for web page use. This discussion will further examine these scanners for different media sizes. The intent is still to produce web images rather than prepress materials. Since web use is the object of this exercise, some discussion on how these images will be viewed is appropriate. Web browsers are used by a computer with a graphics monitor. These monitors vary in physical size from 14" to 21", measured diagonally. Apart from this physical size, a computer system can have the display system set for different resolutions of maximum image sizes. For example, 640x480, 800x600, or 1024x768. What this means is that each monitor unit (the display tube sitting on your desk) can display any of these maximum resolutions. The effect of a specific size monitor displaying different resolutions is that as the resolution in increased (towards the 1024x768 setting), the overall size of the image decreases but shows more items in the display--but the items are smaller in size. As the resolution increases and the overall image reduces, some monitors automatically adjust their internal scanning frequencies to re-size the whole picture to fill the monitor's display. Others require frontpanel setting adjustment to re-size the display to its maximum possible size. If the monitor, regardless of size, is set to the same display resolution, a scanned print will display as the same size on each monitor. For example, if a 14" monitor is set for 640x480, then an image file of 640x480 pixels will fill the monitor's screen. Likewise, if a 21" monitor is set for 640x480, then too will the print fill the monitor's image screen. However, if the 21" monitor is set for 1024x768, then the 640x480 print will be half the size that it was on a monitor set at 640x480. The maximum image size that the smallest reasonable monitor can display is based on the display resolution and the print scanning resolution and is independent of monitor size (not considering how difficult it might be to see small features)--the monitor resolution determines the size. Consider the case of a monitor resolution of 640x480. This is standard VGA. The maximum image size in inches is 640/scan res by 480/scan res. Thus, if the scan resolution is 300dpi, then an original image of 2.13" x 1.60" will fill the screen. If you take this same image file and display it on a 13", 14", 15", 17", or 20" monitor that is set for 640x480, the image will fill each monitor's screen. However, if you take this same image and send it to the same monitors that have been set for 1024x768, then the image will fill half the screen of each monitor. The image will be easier to see and discern as you move towards the larger monitor size. But the ratio is the same. Suppose that you want to display your work at a specific physical size on the screen. For example, 5"x5" for your 5x5" enlarged prints from 6x6cm negatives. Here you have an original at the size that you want it displayed. What scanning resolution should be used? To answer this, we need to determine what resolution is needed for computer display images. A Mac display can typically display 72 dpi; a PC can do 96 dpi. If we split the difference and say that we will display at 85dpi, then we will need 85pixels for each inch that we display. Since we have a 5x5" original that we wish to display at 5x5" (1:1), then we simply scan it at 85dpi. However, suppose that we scan the original 6x6cm (2.25"x2.25") negative or slide? Instead of a 1:1 relationship, we need to increase the size of the original by a factor of 2.22 (5/2.25). If we still retain the final displayed resolution of 85dpi, then we need to scan the 6x6cm original at 2.25 x 85dpi = 188dpi. Note that since the final resolution is the same and that the final image size is the same, the file sizes of both examples will be the same...irrespective of what original was used. The output dimensions and pixel setting determines the file size. What about a 35mm slide? This media is 1.375"x1" (darn close). If we magnify this by a factor of 2.567 we will get a final image size of 3.5"x2.5" which is less than the previous 5x5". However, this is a good size for the following reason. Multiplying 3.5" x 85dpi = 297 pixels. Multiplying 2.56" x 85dpi = 217 pixels. Thus, the maximum pixel resolution is 297 pixels which would allow a 300dpi scanner to scan the 35mm slide and produce a 2.56x enlargement for posting on the Internet. The following table lists some different media sizes and final image sizes based on the previous discussion:
As can be seen, the required scan resolution is the product of the final resolution times magnification. Any scan resolution at the scanner above that listed at the far right will increase the output file size and is unnecessary for achieving the desired final resolution. Does this really work? Let's test it. The Agfa Arcus-II scanner has a control panel in its scanning software that allows the setting of output resolution, scale factor, and type of original (transparent or reflective). Starting with the 35mm slide in its plastic frame, we set the scanner for output resolution of 85lpi, scale factor of 257%, transparent RBG and make the scan. The result is shown in exam1.jpg . This is a 3.5"x2.56" enlargement of the 35mm slide for posting on the web. Suppose we would like a bit larger image? Let's say we want a standard 4x6" image like from a 1 hour photo lab. This is an enlargement of about 430%. So we reset our output specifications in the scanner software and rescan. Note that we did not resize the first scan. If we did, then the enlarged image would be pixelated because we increased the image size without adding new pixels. The result of the next scan is shown in exam2.jpg. The first filesize is 22K while the second is 44K. The 2:1 ratio is consistent with about a 2:1 increase in image size while the resolution remains constant. Look at these images and see if you agree that they look pretty good...good enough for Web pages in fact. As a final test, we scan a 5" x 5" color print that is intended to be the same displayed size. The magnification is 1:1 and scan resolution is 85 lpi. The result of this scan is exam3.jpg. |
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Scanning 35mm negative images (3 methods)
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This above image originated from a 35mm Fuji NPH-400 negative and was scanned from a 4x6" glossy print via a reflective media scan using the Agfa Arcus-II scanner. TIF file size is 357KB; JPG file size is 52KB. Print was scanned at 288 pixels/inch.
This image shown above was made using the Polaroid SprintScan 35 Plus and adjusted in Photoshop to the same 426x285 pixels and 72 lpi as the original print's scan. Negative was scanned at 2,700 pixels/inch. TIF file size is 27.7MB. JPG file size is 36KB.
This image was made as a direct flat bed scan on an Agfa Arcus-II by simply laying the negative strip down on the glass and selecting "Negative" as the image source. Negative was scanned at 600 dpi and the TIF file size is 5.6MB. The JPG file size is 41KB. Conclusion All of the images were adjusted for tone curve using PhotoShop to try to make them all appear about the same. They are all sized to nearly the same direct size: 426x285 and are all 72 lpi. There are more non-image components on the flat bed scan. This probably due to my inability to perfectly clean the transparency adapter glass and the flat bed glass. But you can seet hat the negative is perfect from the Polaroid scan--it has no such anomalies. So which scanner or method is best? Looking at the images, I think the flat bed scan of the negative is best. This is probably because is looks "crisper." But remember that this scanner has a D range of 3.0 whereas the Polaroid has a range of 3.4. When you look at the original TIF files, they are different. There is a lot more information in the Polaroid scan. But for web work? I think that the flat bed does just fine. |
All Photographs Copyright © by Gary Gaugler - All Rights Reserved - Use By Permission Only |