Scanning For Print

This is a Preliminary version of this Page. It just so happened that I was talking to Dean about fixing one of his pictures to print it out, since he'd provided me with a monsterous 300 dpi Jpeg to try to run. It was a bit washed out, and of course, in Color.

This brings me to point 1:

Know what the final goal of your scan is, and work towards that.

In the case of Gallery, that means scanning for eventual output on a 600 DPI Laser printer:

black and white (Laser printers only print black and white)
600 dpi (scaling the image gets seriously funky.) 300 dpi can be acceptable.
7.5" x 10" image area (Because I like 1/2" margins all around)
4500 x 6000 pixels. This is more important. But it's simply 7.5 x 10 inches times 600 pixels per inch.
The resultant file should be saved as a compressed TIFF, or a .gif file, and on average, it will be between 300K and 1 Meg or so in length. If it's larger than this, the format is probably wrong.

So, you've stuck your picture in the scanner, fired up the scanning program, and gotten a 600 DPI scan in raging, full 24 bit color, and loaded it into Photoshop. If you've got another program, you're going to have to fake it.

Well, first of all, you need to do a little color correction more than likely. Dean did this on a tired old scanner at work. You can tell by the Histogram in the levels dialog, it doesn't have any actual black. If you want a good halftone, you NEED solid black. Otherwise your inking gets speckled.

Now, Dean's image was on off-white paper, and the cloud was painted even whiter. You can see the two spikes in the histogram representing the white of the paper (to the left) and the cloud (on the right).

So, you can see I moved the black slider over to where the darker colors start to kick in (I could have moved it even further, actualy) and the white slider past the color of the paper, making the background perfectly white. This is important because otherwise it gets mild dark speckles which look dirty, and ruin the compression.

Photoshop 5, which I have, doesn't allow you to go directly to bitmap, you have to go to Greyscale first. No big deal. Just say Yes when it asks to Discard Color Information.

Now choose Bitmap (or Black and White, or 1 Bit, depending on your software). Photoshop has three ways of making halftones. Two of them suck. This is the good one. You don't want to change resolution. (Well, I suppose you could go to 600 dpi.)

Once you choose halftone screen, after hitting OK, you get this. These are the standard values. Interestingly, there's an inverse ratio between the levesl of "Grey" you can have, and the lines per inch in the Frequency of the screen.

At the 100% magnification, the result looks like this. But remember, this is 100% at 72 DPI, your video screen resolution. When you print it, this particular image is defined as being 300 DPI, so each black dot is merely 1/300th of an inch. This image is roughly an inch square on paper. You can also see that I didn't push the blacks hard enough, so the inking is halftoned.

Now save the picture. TIFF is best, since it keeps the resolution information. GIF is okay, since if you've got a GOOD graphics program, it'll know it's black and white and compress it nice and small, WIHOUT the horrible graphic artifacts you get with JPEG (Which wasn't designed for line art, it's for digital pictures).

Notice the size difference in the resulting files. It's at least a third smaller. It might have gotten even better if I did stuff like erase any stray dots from the white areas, or pushed the blacks harder.