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PostPosted: Sat Sep 11, 2010 8:33 pm 
Hey guys,

Can anyone comment on the below histograms? Basically, I converted an image to B+W with a slight sepia tone (for a more warm look), which means that it's not monochromatic, i.e. the image still has its colour channels.

Anyways, whenever I do the conversion, my histogram changes from a relatively smooth curve (the first image) to the spiked curve (second image). I don't think this is a posterized image, because as far as I understand, posterization is when gaps occur between vertical bars, however, I want to make sure that this assumption is correct before I send the images off to the printer.

Before

Image

After

Image

Thanks!


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PostPosted: Sat Sep 11, 2010 8:54 pm 
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Does the conversion add some "grain" ?

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Radu
Canon PowerShot S100
Canon 50D , SIGMA 10-20 f3.5 ,Canon EF 24-105 L IS USM, Canon EF 100/2.8 macro Canon EF 50/1.4 ,Canon EF 85 f1.8,Canon EF-S17-85 4-5.6 Old Tamron 28-300 inherited from my Canon Rebel G film camera
Canon580EXII
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PostPosted: Sat Sep 11, 2010 8:55 pm 
Not that I noticed, even at 100%.


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PostPosted: Sat Sep 11, 2010 9:07 pm 
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Then I have no more ideeas, sorry. But if the immage shows no psterization on your monitor I suppose there will be neither on your print.

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Radu
Canon PowerShot S100
Canon 50D , SIGMA 10-20 f3.5 ,Canon EF 24-105 L IS USM, Canon EF 100/2.8 macro Canon EF 50/1.4 ,Canon EF 85 f1.8,Canon EF-S17-85 4-5.6 Old Tamron 28-300 inherited from my Canon Rebel G film camera
Canon580EXII
http://www.errre.net


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PostPosted: Sat Sep 11, 2010 9:13 pm 
I did use a plugin to do the conversion. Silver Efex, simulating film, but I did turn the grain up to about 500 grains per pixel (which should be practically unnoticeable) and I didn't visually see any additional grains during comparison.

You were thinking maybe the grains were causing the spikes?


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PostPosted: Sat Sep 11, 2010 9:52 pm 
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Yes, but I must be wrong. It seems to be a residue from the conversion. More pixels fom a particular tone campared to de adiacent tones, I imagined it like grain.

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Radu
Canon PowerShot S100
Canon 50D , SIGMA 10-20 f3.5 ,Canon EF 24-105 L IS USM, Canon EF 100/2.8 macro Canon EF 50/1.4 ,Canon EF 85 f1.8,Canon EF-S17-85 4-5.6 Old Tamron 28-300 inherited from my Canon Rebel G film camera
Canon580EXII
http://www.errre.net


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PostPosted: Sat Sep 11, 2010 10:11 pm 
It really is worrying though. Don't want to have to pay to get prints done over.

Found this, but not sure how credible a source this is, but from what he says, I should be in the clear.

http://www.ronbigelow.com/articles/posterization/posterization.htm


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PostPosted: Sat Sep 11, 2010 10:27 pm 
posterization in a histogram would be spikes that max out rather than a chunky histogram.

Posterized:

Image

Normal:

Image


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PostPosted: Sat Sep 11, 2010 10:30 pm 
So I should be fine then?

Beautiful shot by the way (even posterized :D)


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PostPosted: Mon Sep 13, 2010 9:24 am 
yes you're fine.


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PostPosted: Mon Sep 13, 2010 10:03 am 
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Did you shoot RAW? Raw tends to have less posterization when you start messing with the colors.

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PostPosted: Mon Sep 13, 2010 6:55 pm 
I did shoot RAW, but I did process the image in photoshop as a TIFF exported from Lightroom (16bit, 350 PPI, AdobeRGB).


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