My negative to positive method on a PC

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Scotness
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My negative to positive method on a PC

Post by Scotness »

I'm having a fair bit of success correcting negatives using Photoshop - this of course isn't on the fly as Paul has been doing with Virtualdub but the same method might be able to be applied if you can get similar filters. The other option too is to run it as a batch in Photoshop on each of your screen grabs.

Anyway I'll run through what I'm doing.

First of all I'll use this negative:

Image

obtained from here:
http://www.adcom.bg/Web/Software/LaserS ... %205_5.htm

first step is just to invert it using the invert function:

Image

Then I go to the levels function and look at the histogram
- first thing to do is to switch the channel from rgb to red:

Image

Then I slide the upper and lower triangles into where the histogram is. This has the effect of finding the upper and lower red values in the scan and mapping them across to the max values possible:

*I should mention too that I'm moving it past the flat black portions of the histograms - I read somewhere that this is just noise - it may or may not be, so try either way and see what works the best.

Image

I then move the middle slider a little to the left or right till the contrast looks alright (highly subjective) - and thisparticular one didn't need to much of a change:

Image

I then REPEAT THESE STEPS for the green and blue channel, and then switch to the RGB channel:

Then I move the middle slider only and get the contrast looking good:

Image

This still didn't seem quite right so I went to the curves function and gave it that classic s-bend that film has:

Image

Slightly larger, this is what it looks like so far:

Image

The greens seem a little over satuarated - especially when compared to the corrected original on their page:

Image

So I desaturated the greens:

Image

Which gave this end result:

Image

- which I'm pretty pleased with, and I think it's even better than their example - note the detail in the print on her top above, which is almost blown out in their example below

Image

Anyway - thought I'd share -- Paul why don't you post the original negatives of the pics you were working on so I can try this on them.

Are there any equivalent histogram based filters for Virtualdub that anyone knows of?

Scot
Last edited by Scotness on Fri Jul 21, 2006 1:52 pm, edited 1 time in total.
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Post by Dr Smith »

Scot. Thanks a lot for that. This is exactly the kind of tutorial that an eejit like me needs. Not that it isn't relevant to old pros either. Has anyone ever suggested adding a 'Back to School' forum to the forum index?
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Post by Patrick »

Excellent work, Scott. The contrast and colours of the corrected image look fab. I'm quite satisfied with the results you got to try the same thing when I take up telecine.

Now the only remaining problem with neg transfers is keeping the film ultra clean.
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Post by Patrick »

I wonder if some of these photoshop features could be incorporated into the Cinecap software...
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Post by Will2 »

Patrick wrote:I wonder if some of these photoshop features could be incorporated into the Cinecap software...
With presets for different negative stocks or lighting maybe, then be able to adjust it manually.
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Post by Scotness »

I think this method works on the principal that original should have all channels represented in the full range of 0-255 - hence the mapping across to that. If you have an original that shouldn't have that - eg a sunset, or a blueish early morning shot, then following this exactly I don't think will work - however by not mapping some of the channels as far - you could probably get it to work. Just trial and error I guess, and the output sliders could also be used to try and effect this.

As far as putting it in cinecap - I've never seen cinecap - but I think the maths of what's going on here is so simple I'm sure it could be.

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Post by paulcotto »

Thanks for the tutorial. Apple is selling Shake for $500.00 now so I may get a copy for color correcting.

http://store.apple.com/1-800-MY-APPLE/W ... 5.7.11.0.3

Looks like a serious price drop. I just downloaded a 30 day trial and it runs fine on my G4 Mac Mini with 1 Gig of ram. I am surprised because Motion2 wont even install because my graphics adapter is only an ATI 9200. I will give it a go on the BlackMagic 10 bit negative files.

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Last edited by paulcotto on Sat Jul 22, 2006 12:45 am, edited 2 times in total.
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Post by Scotness »

Paul coud you post some of your original negs - I'd love to give it a go.

It'd be interesting to try and write a Virtualdub plug in to give you these controls - I don't know C++ but there is a Delphi SDK for Virtual dub filters too.....not that I'm likely to be able to do it though......


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Post by paulcotto »

I will post a short 50 meg clip for you to play with. Give me a little while.

Regards,

Paul Cotto

Scotness wrote:Paul coud you post some of your original negs - I'd love to give it a go.

It'd be interesting to try and write a Virtualdub plug in to give you these controls - I don't know C++ but there is a Delphi SDK for Virtual dub filters too.....not that I'm likely to be able to do it though......


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Post by paulcotto »

What format do you want them in? Uncompressed AVI, Blackmagic 8bit .mov, DV?

Let me know,

Paul Cotto

Scotness wrote:Paul coud you post some of your original negs - I'd love to give it a go.

It'd be interesting to try and write a Virtualdub plug in to give you these controls - I don't know C++ but there is a Delphi SDK for Virtual dub filters too.....not that I'm likely to be able to do it though......


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Post by paulcotto »

Try this VirtualDub MSU Color Enhancement. It has a very nice AutoLevels function>>

http://www.compression.ru/video/color_e ... ex_en.html

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Paul Cotto
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Post by paulcotto »

Here is that clip>>

http://smallgagefilms.com/video/NegScot03.avi

23 Megs.


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Post by Scotness »

Here's a still from my current go at it - far from complete, but I'llhave to try more tomorrow (runningout of time now).

Image

It's quite a challenging clip - knowing what to adjust it to is part of the problem - i take it it's late afternoon, early evening. I want to get it dark enough so those neon lights can glow, but not too dark as it's aboviously not fully night time yet.

I took it to virtualdub - saved it as a bmp sequence and then put it into photoshop - following what's above, more or less. I found a slightly better result by working on the rgb channel first in levels nd pulling the right slider over to where the histogram is and then adjusting the contrast with the middle slider - all before I did each seperate channel. I also cropped it to remove the frame edge soit wouldn't show up in the rgb data in the historam.

There's alot of noise in the image - is that due to the capture?

Anyway I'll keep working on it - any one else giving it a go - I'll post the final clip when i've got the best result I can.

Here's a possibly better version with a bit more fiddling of the straight color balance sliders and the red levels control - flipped the right way too.

Image




Scot
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Post by paulcotto »

I did this in the Apple Shake 4.1 demo. It took a while to grasp the interface but after a while it makes sense. I ran about 6 filters on this clip and exported to MPEG2. I will probably buy Shake soon because it has all the tools they use in Hollywood for color correction and compositing. This clip is very shaky and grainy so just pay attention to the color correction please :)

http://smallgagefilms.com/video/TokyoNegTest02.mpg

The clip will be up shortly.

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Paul Cotto
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Post by paulcotto »

Here is one more shake example. It's a little yellow but overall the colors are good.


http://smallgagefilms.com/video/ShakeNegTest02.mpg

Regards,
Paul Cotto
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