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Half Tone Photo

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Old 08-18-2002, 02:25 PM
Joe Joe is offline
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Half Tone Photo

Anybody have any good tips on how to make a half-tone print look good?

A half-tone is a photo taken from a newspaper or magazine, when enlarged it has white dots all over it.

I don't want it to look painted.

Any suggestions or links to a tutorial would be greatly appreciated.


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Old 08-18-2002, 03:02 PM
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T Paul T Paul is offline
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Halftone Scans

I'm not sure what you are looking for, but here are some scanning hints from Adobe.

To get the best scans, follow the guidelines below:

The key to getting the right resolution for halftones is to scan in relation to the desired line screen frequency. (You'll need to get this from your printer). Once you know this, use one of the following formulas:

a) For halftones with a line screen 133 lpi or higher line screen x 2 x scaling of original

b) For halftones with a line screen less than 133 lpi: line screen x 1.5 x scaling of original

For example, if you're scanning a 3 by 5 photo that will be reproduced at 3 1/2 by 6 inches (120% of original) using an 85 lpi line screen, you would scan at 153 spi (85 x 1.5 = 127.5 x 1.2).
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Old 08-18-2002, 03:57 PM
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Tim_S Tim_S is offline
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First question, is it color or not? Color is much harder since there are 4 screen angles involved (one screen each for CMYK).

The first problem is to scan without creating moire patters from the interaction of the frequency of the scanner pixelation and the line screen frequency of the picture. I believe the formulae that T Paul gave will allow you to scan at a high enough resolution to get the halftone dots as discrete dots, rather than a moire pattern.

Check and see if your scanning software has a descreening option. Some do, and a few of those work well.

Ther following comes from Professional Phtoshop 5 by Dan Margulis. This is for black and white images...

1. Scan the picture at a 15degree angle on the scanner, at the highest resolution possible. Then downsample to the resolution you will work at and correct the rotation. This captures the halftone dots accurately with a minimum of moire, and the downsampling begins to blur the dots, which is what we want...

2. Adjust the contrast to taste.

3. Make 2 duplicates of the image A and B

4. To A, apply a gaussian blur at a fairly small radius to just fill the space white space between dots. (Dan says radius 1 but that will depend). Don't go so far the dots themselves are damaged.

5. Go back to the original image, Apply Image (A) in Darken mode.

6. To B, apply a curve to darken the highlights to about 20%.

7. Still on B apply Dust and Scratches filter at a small radius (Dan uses 1 again) so that the dots diminish slightly, but hold their shape. The lightest dots may go away, that is expected.

8. Go Back to the original, and Apply Image (B) in Lighten mode.
If needed adjust contrast again.

Not quick and simple but it helps. It doesn't make the dots go away, but it can make an ugly picture acceptable.

If your image is a color half tone a good scan angle is often 45 degrees. The process for color adds a few more steps too. First after scanning convert to LAB and blur the A and B channels. Copy the LAB version and convert the copy to CMYK and discard all but the K information. To the LAB picture use the proceedure for descreening black and white above, correct for color and convert to CMYK. Replace the K channel with the K channel saved earlier. Make final adjustments.

End paraphrasing from Dan Margulis

I really compressed the color instruction, but it should give you the idea. If you need more detail, get the book. It will teach you more than you ever wanted to know about color control.

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Old 08-20-2002, 07:27 AM
Joe Joe is offline
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Join Date: May 2002
Location: CT
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Thanks for the relies!

Well. it is B&W and it's a photo from an old passport, so it's small.

He wants it enlarged to 5X7.

I was thinking about your process and remembered I gave the photo back to the person after I scanned it.

So my first job is to try and get the photo back.

Thanks again!


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