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How to convert negatives to positives

Steven Sandberg , May 20, 1998; 08:34 p.m.

I'm using a regular flatbed scanner with photo shop. I'd like to know how to convert the negative image to a positive.

I understand that the film negative is not a true negative in the sense that the color space is tinted orange.

I have already searched the archives and other article concerning scanning negatives do not discuss the details of converting them to positives.

Responses

erick -- , May 20, 1998; 10:20 p.m.

It's my understanding that you need to have a "transparency adapter" to scan from negatives on a flatbed scanner. A straight scan + invert in photoshop won't preserve the correct color.

Ron Gemeinhardt , May 20, 1998; 10:58 p.m.

You could try filtering out the orange bias before inverting the scan. In 35mm, there's usually a fully blank frame somewhere on the roll (e.g., neither of my cameras can use frame 00/00A). If you scanned that, you'd have a full-frame orange field, uniform with any luck, which you could then subtract from all other negatives scanned from the same roll. Inverting the result should give you a correctly-balanced positive.

If this works, you might need to scan a blank frame for each film type (or each roll?!) in case the color bias varies.

erick -- , May 21, 1998; 09:31 p.m.

This is really great! I received two "you don't get it!" e-mails from him today, and though I wasn't really enamored by the tone, I thought his explanation here was much better than his original question.

Since I'm also looking for the answer to Tzvi's quest, I think it'd be helpful to add this further explanation to the discussion.

PS -- My guess is that Philip would know the answer to this question. _______________ From: Steve Sandberg To: ekyogoku@uclink.berkeley.edu Subject: Response to How to convert negatives to positives > PS I actually do understand the problem -- I once tried scanning No you DON'T understand the problem. There are 2 things going on here and you've got BOTH of them wrong. You can't tell me what the right way of doing it is because you've never done it. Problem #1 is you don't have any light behind the slide. Problem #2 a color negative is NOT the negative of a color slide. A transparency adapter is not going to correct Problem #2. As far as Ron's suggestion, he's ALSO wrong. A blank frame doesn't have any die on it. Thus it only color corrects black, which didn't really need color correction. The only correct way to do what Ron is suggesting is to take a picture of red, green, and blue and scan in those 3 frames.

Steve Graham , May 21, 1998; 10:58 p.m.

Most transparency scanners (and decent flatbeds with transparency adapters) have the facility within their scanning software to carry out the conversion from a negative image to a positive one. You select colour negative as the input format and the software and scanner do the rest. My Minolta Dimage films scanner does a pretty good job of it, as does a colleagues Powerlook II flatbed (with transparency adaptor). In my early scanning days I tried doing negatives and transparencies on my Microtek E3 without transparancy adapter - using a lightbox for backlighting. The results were real crap, for a number of reasons :-

1) The 300x600dpi optical resolution of the E3 is way too low
2) Transparency adaptors disengage the internal light of the scanner while in use - not doing so when doing film scans seems to cause flare like problems.
3) The input source film types in the scanning software were disengaged when no trannie adaptor was in place - leaving me to do the conversion to positive in PhotoShop.

Bottom line is that if you're scanner supports a type of colour negative as an input source you can reasonably easily get a decent results. If not then it's very difficult to do so. I remember reading a theory somewhere that stated that the orange base was not of a consistent colour and density, and only the scanning software was really optimised to cope with this. Not sure if thats true or not.

P.S. contrary to popular opinion both the Powerlook II flatbed and the Minolta Dimage films scanner seem to give better results with slide film (especially Astia) than they do with negatives.

erick -- , May 24, 1998; 08:22 a.m.

I picked this up on a different forum.

Even though Steve/Tzvi is brutally rude, I think/hope this information will be of use to him or others on this forum:

In order to scan transparencies - negs or slides- you'll need a tranparency adapter, as the light will have to pass through - not be reflected from- the tranparency. The "orange tint" ( the integrative mask) on the negative can be dealt with by your can program, under mode choose transmissive: negative and the right film type (kodak/fuji/agfa whatever relevant) however this is a defalt setting only, which still might need quite a bit of retouching to get the exact tonal range. Of course this also depends on the type of output you want afterwards, so work on test images in order to optimally callibrate your system, only then go to "real work"

erick -- , May 24, 1998; 12:07 p.m.

Here are some potentially useful references. Hopefully Steve will not send me more rude and obnoxious e-mail attacks as a result of me posting this: _________________

You need a transparency adapter to provide a light source to shine through the film (as opposed to reflecting from a print).

A couple of references:

Wayne Fulton discusses transparency adapters in his scan basics:

http://www.cyberramp.net/~fulton/scans.html#menu or direct to page at http://www.cyberramp.net/~fulton/basics12.html

While the MagicScan driver for the UMAX Powerlook should take care of orange mask removal (from color negatives), you can see an example of a Photoshop technique for negative-to-positive that includes this at

http://www.interlog.com/~pinkster/photo/neg2pos/neg2posa.html

Philip Greenspun , May 25, 1998; 11:32 p.m.

http://photo.net/philg/photo/orange-negative-mask.html covers the issue of why there is an orange tint.

Correcting it in PhotoShop is a pain, which is why film scanners come with software to do it before the bits hit PhotoShop.

Philip Greenspun , May 25, 1998; 11:33 p.m.

Oh yes, I should hvae noted that if you'd taken the time to browse the digital imaging thread archive, you'd have found

http://db.photo.net/bboard/q-and-a-fetch-msg.tcl?msg_id=0005Q1

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