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Author Topic: Conversion of negative image  (Read 843 times)

ahbnyc

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Conversion of negative image
« on: September 29, 2017, 12:43:32 AM »

I was at Photoville in Brooklyn last weekend (great fun) and had my picture taken with a pinhole camera and was give a print. I scanned it and imported it into Lightroom. The print is essentially a negative image.  I would have thought that there would be something I could click in Lightroom to convert it into a positive image by converting blacks to white and darks to light and vice versa but couldn't find it -- I think there used to be a simple way to do it in Photoshop Elements which I no longer have on my computer. Am I missing something? I was able to get most of the way there by using the tone curve but couldn't easily get it totally inverted and thought there must be a simpler way.
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john beardsworth

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Re: Conversion of negative image
« Reply #1 on: September 29, 2017, 03:36:38 AM »

Lightroom was intended for a wholly-digital workflow, so maybe you shouldn't expect it to have a negative conversion feature.

If the file is raw, you can drag the Tone Curve to a negative shape, as you have found. That's the only way, but you can totally invert if you're careful. If it isn't raw, Photoshop or a pixel editor is your best bet.

John
« Last Edit: September 29, 2017, 03:56:26 AM by john beardsworth »
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bns

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Re: Conversion of negative image
« Reply #2 on: September 29, 2017, 05:32:42 AM »

RAW or JPG does not matter. Simply turn the tone curve around to a -45 degrees slope. You can set that as a custom preset as well.

Boudewijn Swanenburg
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TonyW

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Re: Conversion of negative image
« Reply #3 on: September 29, 2017, 05:40:16 AM »

I agree with John that PS or similar is somewhat easier to edit this type of image, but LR will do the job quite well.  One workflow:

1. Invert the image by using the tone curve to drag the RGB black and white points to opposite points vertically.  Your image will probably have a strong cast usually Cyan but is part way there

2. Adjust the individual R, G and B channels to bring the end points into where the histogram begins (experiment until correct)

3.  Fine tune using the Tone curve as required and any other LR tool

Attached quick animation showing roughly the steps.  This is not my original image and but is one that I have used in the past so credit and copyright to the original photographer
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Mark D Segal

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Re: Conversion of negative image
« Reply #4 on: September 29, 2017, 07:58:00 AM »

Scannerless Digital Capture

Scanning Colour Negatives

There are elements within these two articles that may provide some useful insight for various approaches you could take.

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Mark D Segal (formerly MarkDS)
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ahbnyc

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Re: Conversion of negative image
« Reply #5 on: September 29, 2017, 03:49:07 PM »

Thanks to all for their input! I will continue to tweak the tone curve.
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alan_b

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TonyW

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Re: Conversion of negative image
« Reply #7 on: October 03, 2017, 07:32:58 PM »

What are people's takes on this theory/method?

Orange Mask Removal, Burton's Technique: dpreview forum
Removing Orange Mask from Colour Negative Scans: filmshooting forum
I have not tried either of these methods and TBH I kind of lost interest after convert to 8 bit and CMYK. 

On the very odd occasions that I have been presented with a colour neg scan a similar method to my link has always been good enough.  Neutralising the mask first sounds ok but may not be necessary as using curves and other PS tools may get the job done quicker.

I would be interested to see a real world test that demonstrates any superiority of one method over another
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BartvanderWolf

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Re: Conversion of negative image
« Reply #8 on: October 03, 2017, 07:43:54 PM »

I have not tried either of these methods and TBH I kind of lost interest after convert to 8 bit and CMYK.

Same with me.

In addition, it already assumes a flawed 'scan'. A proper scan will already compensate for the mask color, either by adjusting the scanning light's R/G/B channel exposure times which will optimize the Signal/Noise ratio, or the scanlight's color, and neutralize the (after inversion) black-point.

Cheers,
Bart
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Mark D Segal

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Re: Conversion of negative image
« Reply #9 on: October 03, 2017, 07:57:50 PM »

Same with me.

In addition, it already assumes a flawed 'scan'. A proper scan will already compensate for the mask color, either by adjusting the scanning light's R/G/B channel exposure times which will optimize the Signal/Noise ratio, or the scanlight's color, and neutralize the (after inversion) black-point.

Cheers,
Bart

Well that raises a more generic point: there seems to be a lack of recognition on the part of those proposing very convoluted workflows that the most prominent scanning applications such as SilverFast and Vuescan had already developed very satisfactory algorithms for inverting colour negatives, which includes for dealing effectively with the orange mask.
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Mark D Segal (formerly MarkDS)
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alan_b

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Re: Conversion of negative image
« Reply #10 on: October 04, 2017, 01:44:07 AM »

I have not tried either of these methods and TBH I kind of lost interest after convert to 8 bit and CMYK. 

On the very odd occasions that I have been presented with a colour neg scan a similar method to my link has always been good enough.  Neutralising the mask first sounds ok but may not be necessary as using curves and other PS tools may get the job done quicker.

I would be interested to see a real world test that demonstrates any superiority of one method over another

I thought it was interesting from an academic perspective, a deconstruction of the negative structure.  I dropped it upon remembering that I didn't selectively mask channels when making color prints in the darkroom - just dial in the color balance and go.

BartvanderWolf

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Re: Conversion of negative image
« Reply #11 on: October 04, 2017, 11:28:57 AM »

I thought it was interesting from an academic perspective, a deconstruction of the negative structure.  I dropped it upon remembering that I didn't selectively mask channels when making color prints in the darkroom - just dial in the color balance and go.

No problem with you sharing the links, but as Mark said, the more popular Scanner softwares already know how to deal with the yellow/orange masked Color Negative films, if possible on a hardware level of the scanner (changing the relative R/G/B channel exposure times). They further have a choice of characterizations for many types of Color Negative films to deal with the specific absorption spectra of the dye-sets used. Both SilverFast and VueScan are popular for a reason.

Cheers,
Bart
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