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[John Gregson]

Hi All,
I run a Risograph (Glorified photocopier) printer which I use for cheap single colour flyers. Some customers are wanting photos on their flyers but the riso effort looks, well - crap. Can anyone point me in the right direction, using either photoshop 5 or coreldraw x4, on how to covert a photo to a halftone image.

Doesn't have to be fine detail, but an image that could work on a riso come photocopier.

Cheers in advance - John

[James Martin]

On my Photoshop its filter/sketch/halftone or am I not getting the point as it wouldn't be the first time?

[John Gregson]

Hi James,
I think the riso works in a similar way as screen printing so the photo would need to be in black and white, not shades of grey. So far I have tried changing to greyscale then bitmap, Method - halftone screen. Its the frequncey, angle and lpi I need to get right. Thought i'd cracked it but when imported into corel it loooked like $h-te

This is the same or similar method used for the photos in black and white newspapers.

Cheers John

[David Rogers]

Couple of links to past topics of halftone, rasterise & dither.

http://www.uksignboards.com/viewtopic.php?t=37991&highlight=dither

http://www.uksignboards.com/viewtopic.php?t=17042&highlight=halftone

http://www.uksignboards.com/viewtopic.php?t=17762&highlight=halftone

Dave

and a few links to other 'how to' topics.

[John Gregson]

Thanks for that David, I can see this being very trial and error but I think its the right direction.

Cheers John

[Stuart John Halliday]

John,

Sounds like you are nearly there.

You need to make sure that your image is correct size in mm/inches before converting grey scale image to bitmap.

When converting to Bitmap increase your output resolution to that of your output device (say 600 ppi). This will enable the final halftone frequency (say 35lpi) to be interpreted without being to low a resolution.

When viewing in Corel this may look very poor quality (moire). You need to zoom in 1:1 to see quality of print. Do not then try and inlarge image before going to print as this will pixelate and change your desired lpi.

[John Gregson]

Hi Stuart,
Thanks for the info - i dabbled last night but didn't have a printer handy so just viewed in corel and your right, it looked bad.

I'll have another go now I'm at work and see what happens.

Cheers John

[OwenTaylor]

I sometimes use this free tool for creating half tone images. Its a simple standalone program called the rasterbator. It converts images into halftones in pdf format that can then be opened in Illustrator/Corel etc. Simply download it and run the program and follow the instructions or you can use the online version.

Quick hint - the program creates the halftones in a vertical/horizontal grid. What I have found is that halftones usually look better when they are at an angle so I normally rotate my image 45 degrees in photoshop and save as before rasterbating!

It can be downloaded here:

http://homokaasu.org/rasterbator/

[John Gregson]

Cheers Owen, I tried downloading that program at home last night and it froze and crashed the laptop. Just tried again at work and the same thing happened.

Could be the program - or it could be Norton as I've got Norton 2010 Internet security running on both computers.

Cheers John

[OwenTaylor]

That's strange. I've been using it for years without any issues. Maybe give the online version a go.