Help me get a grasp on resolution dpi and the like when scanning...

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ian80

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Jul 26, 2002
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Hi guys,

I understand the difference between dpi and ppi. I get the concepts of digital imaging. However, getting things to work right with my scanner is another story. So let's just see if you can't walk me through this specific problem.

I have a website where I post little drawings I do in my sketchbook. Originally, I was drawing them in my sketchbook, redrawing them with in painter with me Wacom and then posting them. Well, now I have a scanner, so I want to cut out the middle man.

My problem is this: I get the scanned images to look right. They are either too big once in IE, or I shrink them down in size and the image quality goes to hell. The images are roughly 2 inches square. I want to scan them in, have them be approx. 8 inches square when displayed in IE at 1024x768 and have them still look good (not pixel-y).

There are about 10 images to a page when I scan them in, then I just crop each one. I am trying to enhance work-flow, so I want the scanned-in image (8.5 x 11) to be the right size/resolution from the beginning, so that once cropped, the images are ready to post.

There is another issue: file size. When I was drawing them in painter, they were coming out at about 14 kb. For some reason the images I'm scanning in, even when cropped down and at the same resolution are equaling 150 kb in size.

Can anyone help, I can't seem to get it.

Thanks!
 
Joined
Jun 27, 2000
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The size part is pretty simple math. I would guess 19 inch screens are about average and they are around 15 inches wide. If 1024 pixels covers 15 inches you need around 550 pixels wide to cover 8 inches of screen width.

Measure one of the sketches you will post while it is on the sheet of paper. If it ends up 3 inches wide, divide your 550 pixels by 3 inches and scan at 180 PPI to end up with an image that will stretch 8 inches across a 19 inch screen at 1024 X 768.

If your drawings are simple black and white line drawings you might want to scan in 1 bit black and white. On Microtek and Umax scanners it is called “Line Art”. On others it is just “black and white” where there is also a “grayscale” choice. With 1 bit black and white you get the most aliasing or “jaggies” since software can’t soften the edges with anti-aliasing. On the other hand you get the sharpest looking images. If jaggies are a problem your only choice is to scan in grayscale or convert to grayscale with anti-aliasing. If your sketches are colored you have to scan in RGB of course.

File size is dependent on the dimensions in pixels, color depth, file type and compression. 1 bit B&W files are smaller than 8 bit RGB or grayscale but they can’t be compressed. The smallest grayscale or color files come from JPG compression. The more you compress the more artifacts and the lower the quality, but for viewing online you can go to a pretty high compression if people won’t be downloading and printing the sketches.

The reason the Painter files were so small is that they are vector images. Vector files just store data about the images like position of the start and end of a line with curvature. The files end up very small and you can enlarge them without degrading the quality. Scanners scan only in raster by recording dots and the files are larger. You also can’t enlarge the resulting scan very much without degrading quality.
 

Noyb

Jay
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Do you have an Image viewer and editor program that can crop and resize images ?

One of the favorites here at TSG is the freeware Irfanview ...
http://www.irfanview.com/

I usually scan at a high resolution then crop and resize later as needed.
 
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