converting color scan to B&W

[ktinkel]

I have a bunch of line-art pages (drawings, typewriting, handwriting) that were offset printed in black ink on a textured pumpkin-colored stock.

I need to scan them and turn them into B&W (for the web; but who knows about the future and these are somewhat fragile, so I am working large), but I’m not positive how to proceed.

So far I tried this:


scan at 300dpi in 24bit color (and save it)
convert to greyscale in Photoshop (and save it)
use Levels to make the background white
change Mode to bitmap using Threshold 50%
That leaves me with a huge and bumpy image; reducing it to its original physical size should fix the bumps, but I wonder whether I should have adjusted the size when I changed mode. Or whether I am going about this all wrong.

This was an easy one: some large-ish handwriting and a big drawing. Some of the others are typescript (some with ribbon typewriter, even); one has better typewriting (electric typewriter) but it has been reduced to 50%.

Any advice before I get in over my head? Thanks.

[iamback]

I have a bunch of line-art pages (drawings, typewriting, handwriting) that were offset printed in black ink on a textured pumpkin-colored stock.

I need to scan them and turn them into B&W (for the web; but who knows about the future and these are somewhat fragile, so I am working large), but I’m not positive how to proceed.

So far I tried this:


scan at 300dpi in 24bit color (and save it)
convert to greyscale in Photoshop (and save it)
use Levels to make the background white
change Mode to bitmap using Threshold 50%
That leaves me with a huge and bumpy image; reducing it to its original physical size should fix the bumps, but I wonder whether I should have adjusted the size when I changed mode. Or whether I am going about this all wrong.I'm not sure what the last point means (PS specific?) but it sounds like you're turning it into pure black-and-white?

After (or before) your third step, try using a histogram adjustment to just make it a very high contrast image, so you'll keep some anti-aliasing. Instead of straight conversion to greyscale you could also just turn the saturation all the way down, or split into separate (R, G, B) channels and pick one of them to work on.

Just try different approaches and combinations until you find what works best.

[Bo Aakerstrom]

All I've ever had to do is to convert to greyscale, then play around with the brightness and contrast settings.

I'm sure the level of success with this method depends on how pronounced the background colour is as well.

I'm also quite sure that someone has got a better method - I've got my notepad at the ready!

[ktinkel]

I'm not sure what the last point means (PS specific?) but it sounds like you're turning it into pure black-and-white?

After (or before) your third step, try using a histogram adjustment to just make it a very high contrast image, so you'll keep some anti-aliasing. Instead of straight conversion to greyscale you could also just turn the saturation all the way down, or split into separate (R, G, B) channels and pick one of them to work on.

Just try different approaches and combinations until you find what works best.Well, that’s what I have been doing, which is why I decided to cry for help! <g>

Yes — Threshold is one of the conversion options (along with types of dithering).

Using Levels is using the histogram — I use the white selector and click on the orangey background. Voila! It all turns white.

I think I will look at the channels; forgot to try that.

Thanks.

[annc]

Why not just use the Blatner process for line art as outlined in Real world Photoshop (which I know you have)?

[ktinkel]

Why not just use the Blatner process for line art as outlined in Real world Photoshop (which I know you have)?Yep — and I use that for detailed line art that I scan as greyscale.

But the color shift seems to make a difference. Maybe I will go back and do that more methodically.

Thanks.

[terrie]

Try using a Channel Mixer adjustment layer on the rgb file with the monochrome option checkmarked...it probably won't make much difference since all the channels are probably the same but it might...

Terrie

[iamback]

Using Levels is using the histogram — I use the white selector and click on the orangey background. Voila! It all turns white.Yes, but using Levels is using the histogram only indirectly - and with much less control. Since I found that out I never use it any more. There's a lot more to histogram adjustment than picking a white point. Use the histogram and play with all the controls - with a preview on your full image.

[ktinkel]

Yes, but using Levels is using the histogram only indirectly - and with much less control. Since I found that out I never use it any more. There's a lot more to histogram adjustment than picking a white point. Use the histogram and play with all the controls - with a preview on your full image.Ahhh — that means the dread Curves, I suspect. I find that extremely intimidating, but suspect you are correct.

Thanks.

[ktinkel]

Try using a Channel Mixer adjustment layer on the rgb file with the monochrome option checkmarked...it probably won't make much difference since all the channels are probably the same but it might...Okay. First I will go figure out what the Channel Mixer is, and then tiptoe into an adjustment layer (which I have never understood — I usually just plow ahead, then use the History box to abandon everything and start over.

:eek:

[terrie]

kt: Okay. First I will go figure out what the Channel Mixer is, and then tiptoe into an adjustment layer (which I have never understood — I usually just plow ahead, then use the History box to abandon everything and start over.ROFL!!!

Channel Mixer is quite cool...accessed via:

1. Layer > New Adjustment Layer > Channel Mixer

2. or the 4th icon at the bottom of the Layers palette

An adjustment layer is a wonderful tool because it creates a layer (duh!) that allows you to play (levels, curves, hue/staturation, channel mixer, etc) with the original image in a non-destructive way.

I use them all the time. For example, I always use a Levels Adjustment layer rather than just performing the Levels command (Image > Adjustment > Levels) because I don't have to dup my original layer (always keep an original version of your image) and I can go back and play with the adjustment layer settings later if I need/want to.

Once I have the adjustment as I want it, I usually then add a new layer above the adjustment layer and to a merge visible merging the original image layer with the adjustment layer(s) onto a new layer...

With Channel Mixer, I usually open the Channels palette to see which of the channels will give me whatever it is I need--which one is best for whatever it is that I'm doing with the image--and then I go back to the Layers palette and get a CM adjustment layer, check the "Monochrome" option (if I'm going to greyscale), and choose the particular channel I thought would be best setting it at 100% and then add (or subtract) the other channels in the CM window until I get what I want.

The rule of thumb is that all the channels percentages should add up to 100% but it's not a hard and fast rule and you having settings that add up to more than (or less than ) 100% is fine--you won't get an error or anything...

If you want, email me (74727.3164@compuserve.com) one of your RGB scans and I'll play with it for you...

Terrie

[iamback]

Ahhh — that means the dread Curves, I suspect. I find that extremely intimidating, but suspect you are correct.Actually, that's not what I meant, but I didn't make myself clear enough.

What you're doing apparently is nothing but 1) convert to greyscale and 2) set a white point using the dropper tool in Levels (which does include the histogram). What I mean is, use the sliders and/or the input/output levels entry boxes on the histogram itself to change its appearance. You could do that also before conversion to greyscale and work on the separate channels first to get rid of (most of) the color before using some method to convert to greyscale (directly, or by decreasing saturation).

But using Curves is yet another method to try :)

Some hints about using Levels in PS:
http://www.cambridgeincolour.com/tutorials/levels.htm

[ktinkel]

What I mean is, use the sliders and/or the input/output levels entry boxes on the histogram itself to change its appearance.Those are in the Curves function, or I am missing something (which wouldn’t surprise me — I am a vector dolly, not a bitmap one!).

However, I got the one piece to look pretty good at the size I need to use it. I will attach it. (The writing was done with a fuzzy marker — the fuzziness is not a result of my manipulation. The bumpy paper may have exacerbated it, though.)

[iamback]

Those are in the Curves function, or I am missing something (which wouldn’t surprise me — I am a vector dolly, not a bitmap one!).Hmm - did you look at that tutorial I linked to? It has screenshots showing the Levels dialog in PS, with sliders, input/output settings boxes and droppers. Not having PS myself, that's what I'm going on. (I've seen similar in other tutorials and normally have no problem "translating" usage of that dialog from PS to the equivalent in PSP.)

However, I got the one piece to look pretty good at the size I need to use it. I will attach it. (The writing was done with a fuzzy marker — the fuzziness is not a result of my manipulation. The bumpy paper may have exacerbated it, though.)It does look pretty good - I'm just wondering if the "fuzzyness" as you call it could be made less by using a different method. Have you tried any sharpening on it? Or (before) increasing contrast?

[ktinkel]

Hmm - did you look at that tutorial I linked to? Not yet, but I will.

I'm just wondering if the "fuzzyness" as you call it could be made less by using a different method. Have you tried any sharpening on it? Or (before) increasing contrast?I don’t think I did sharpen that one, but I usually do sharpen, at the very end.

I’ll keep plugging away. They tell me learning new stuff is good for the brain. <g>

[iamback]

I’ll keep plugging away. They tell me learning new stuff is good for the brain. <g>Not just that - keep your brain active and you'll live a longer life!

(Exercising mine quite bit today, installing new network hardware...)

[dogmandouglas]

As a commerical printer I have found that 300 ppi is not enough resolution for line art. The minimum scan in greyscale should be at least 600 ppi. This ensure that when you change from greyscale to bitmap you will have fewer jaggies. Try it and see.

[annc]

As a commerical printer I have found that 300 ppi is not enough resolution for line art. The minimum scan in greyscale should be at least 600 ppi. This ensure that when you change from greyscale to bitmap you will have fewer jaggies. Try it and see.That agrees with what David Blatner recommends in Real world Photoshop.

[ktinkel]

As a commerical printer I have found that 300 ppi is not enough resolution for line art. The minimum scan in greyscale should be at least 600 ppi. This ensure that when you change from greyscale to bitmap you will have fewer jaggies. Thanks. And no questionIn my years as a graphic designer, I used to prepare line art at 1200 dpi for that reason. Above that yields diminishing returns, but below that, you can often see jagged lines.

These are for the web, which is a whole different kettle of fish. And the art is being reproduced from printed copies on textured brown paper. (At least the paper is legitimately brown, not screened ink!)

If I can get them to look okay on the screen, then I will be happy. But the battle between not very dense blacks (broken ribbon typewriter and the like) and the extremely dense orangey-brown background is what has me struggling.

Terrie’s suggestion to work with just one channel seems promising, however.

[terrie]

kt: Terrie’s suggestion to work with just one channel seems promising, however.Oh good...I love Channel Mixer...'-}}

Terrie