Can anyone claim to have a scanner that can produce an image that is of a 1:1 ratio with the original image? The select group of scanners I have tried always generate a larger image. (Or, is it the software?)
Any insight would be appreciated.
I would guess it’s the software. The assigment of a scale in the image file is pretty arbitrary. I haven’t checked my scanner, but I expect that it stores an appropriate DPI in the image file. After that there’s a lot of variables involved in geting exactly that many dots per inch on paper.
In the cases with which I’m familiar where the exact scale matters (CAD, vectorization of raster images and using raster images as background for precise vector images) there are scaling commands with essentially arbitrary precision. The nastier problem is nonlinearity, and the programs I’ve seen all have “rubber sheeting” capabilities to help compensate for nonlinearity.
jrf
JonF, the problem of “nonlinearity” you mention: Is that the problem of knowing which pixel to turn on when a line does not fall nicely along the horizontal, vertical, or a 45 degree angle?
I’m missing something here. When I scan a 4x6 snapshot, Photoshop gives me a 4x6 image.
Are you scanning the entire bed rather than just selecting the area of the image on the bed?
Doesn’t your s/w permit you to select the limits of the area to be scanned?
Me too, what I scan, I get.
Although scanning a regular US dollar bill doesn’t seem to come out as the exact size when printed. No that I do that anymore, see.
I have that problem with the 6000 series HP scanner we have at my clients office.
No matter what settings I have it still comes out to a huge size. It sucks because you loose a lot, I don’t care what anyone says, when you reduce an image in Photoshop or anyother program.
No. I forget the name for the effect that you mention.
The nonlinearity I mean can be due to a nonlinearity in the original photograph (or whatever), the original’s paper stretching unequally, the scanner head not moving at absolutely constant velocity (I think some lower-cost scanners “snapshot” lines at constant time increments, rather than triggering off a movement sensor), or maybe other things. It results in a non-constant DPI at various parts of the image.
jrf
I hesitate to mention this, because it’s so obvious that surely you’ve thought of it…
but are you scanning the image at the same resolution as your screen? If your screen has 72 dpi and you’re scanning at 100 dpi, obviously the image on the screen is going to be larger.
The other thing, which isn’t quite so obvious, is that your listed screen resolution is probably just a rough estimate. Particularly if you’ve got a fancy monitor that allows you to adjust aspect ratios and things like that.
The term for the stair-step “jaggies” effect is “jaggies” colloquially, and “aliasing” more formally. To get rid of it, you do “anti-aliasing”, which uses shades of gray (or whatever) when a pixel is less than 100% but more than 0% filled by the ideal line you’re trying to draw.
The size the image displays as depends partly on the resolution of the video output on the computer, and partly on the resolution of the scan (set by the software).
Let’s say you scan an image and it becomes an image file that is 320 x 240 pixels in size. Let’s say the computer you are using displays a resolution of 800 x 600 and the size looks about right, but then you save the file to disk and bring it to another computer which is using a resolution of only 640 x 480. The very same image will now look about half-again as big as it did before, even though it’s exactly the same.
This also goes for scanning resolution: if you turn up the resolution on the scan, it will make a larger file, since larger files contain more data. If you are not concerned about the quality of the image and simply want something that is the same size, turn down the resolution of the scan in the software options.
The problem with displaying images on a computer screen is that they can only display at one resolution. Unless you use vector images, it is not possible to reduce an image’s size and retain it’s quality.
Some interesting thoughts that bring up the idea that we may be using the same words to say different things.
As in my first response, if I scan a 4x6 snapshot, Photoshop gives me a 4x6 image - printed. I can display it on my screen at any size I choose - REGARDLESS of resolution. But when I show the image rulers, I’ve got the dimensions I scanned.
File size is, of course a function of both image size and resolution. I am now confused about the OP.
Techchick - I think you just made me glad that Santa didn’t bring me the HP 6000 series scanner. I’m happy with my WYSIWYG umax.
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- The term I have heard to describe photos digitized at low resolution is- -“pixellated”.
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- The problem you describe is computer line-drawing; there are a few different reasonably-good ways to go about it, epending on how fast you want to draw your lines and how fast your computer is. Many methods use Bresenham’s algorithm or some variation. - MC
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techchick68, better check you scanner software setup to make sure its set right. You may have it set to magnify 
Rather than scan at the original size.
handy,
I haven’t really had time to sit down and play with the software a lot as it’s a work scanner.
When I have messed around with it, it just frustrates me. I have Photoshop, but even in PS if your image is huge and reduce it a ton, you loose a lot of the essense of the photo.
I will be purchasing my own scanner in the next few months, I want a high quality one since half of my income comes from web design. Any suggestions are appreciated
techchick68, by the time I mentioned one, it wouldn’t be for sale anymore. Check that you get a legal size scanner rather than just 8.5 x11", USB scanner or parl port scanner?
I never scan over 300 dpi because the web is 72 dpi. At a resolution of like 1000dpi, a 4" x5" would probbaly be around 100 megs…
So what exactly are you using the scanner for? What software do you usually use? When you say the image is huge, are you saying you can only see a small part of it on the display? Or are you printing it out and the printout is larger than the original? Or is the file size too large?
There are different kinds of ‘sizes’ of a scanned image. How much detail is available in the image depends on how many dots (pixels) the image file is made up of. The size of the image when printed out or displayed on the screen can be any size you want, and is independent of the pixel size of the image. Printing a 300x300 pixel image at 300dpi results in a 1x1 inch printout, or a 3x3 inch printout at 100dpi.
OK, I read the OP again and am going to guess that you are scanning an image and printing it out, and the problem is that the printout is too large. One possibility is that your software does not handle DPI (resolution) settings at all. I think my old copy of PaintShop Pro is like this - it only knows the pixel size of the image, and doesn’t even know what the physical size of the image should be. On such software, you can usually specify the size when printing it out.
Another possibility is that the scanner is not reporting the DPI setting correctly to the graphics software, or the graphics sofware isn’t understanding it. In this case, you can manually change the DPI setting. On PhotoShop, for example, go to Image menu, then to Resolution settings. You can change the DPI setting (it may be called Resolution) or the physical size there. The trick here is NOT to click on the ‘resample image’ tab. This way, no information is lost or even changed. It only tells the program what the physical size of the image is, so it can print it to that size.
In any case, I have yet to see a scanner which, if set up correctly and with the proper software, does not produce 1:1 printouts. Unless you count the sheet-feed scanner which often end up with 1:0.98 to 1:1.02 or so ratios, due to the paper slipping on its way through the scanner. (VERY annoying if you’re trying to scan forms and fill them out on the computer, but otherwise not even noticeable)