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Mustafa Umut Sarac
04-30-2010, 08:40 PM
I opened with Lightroom , many Autochrome images which I found from web and coming from WW1 French Army.

I found something very interesting , histograms are fully flat and horizontal without showing any color graphic in it.

How do you comment this ?

Best ,

Mustafa Umut Sarac

Istanbul

glbeas
04-30-2010, 09:33 PM
Sounds like an artifact of post processing after the images were scanned.

Mustafa Umut Sarac
04-30-2010, 09:42 PM
Images were very beatiful to watch. Why you would want to do it and how ?
Does it easy to clean and flatten the histogram ?
What is the meaning of clean and flat histogram ?

Lots of questions but I cant go to sleep now ! You know..

Best ,

Mustafa Umut Sarac

Photo Engineer
04-30-2010, 10:05 PM
It may reflect an additive system vs a subtractive system.

PE

Q.G.
04-30-2010, 10:17 PM
Then changing from RGB to CMYK and back again would change that, wouldn't it? But will it? It's an image file, viewed on, and made for a computer screen. So it's always additive.

Histograms do show distribution of brightness. Not necessarily of the original, but certainly of the file, i.e. of a converted representation of an original.
You are saying, Mustafa, that for each of the colour channels contained in the file's colour mode, the histogram is flat?

Mustafa Umut Sarac
04-30-2010, 10:21 PM
Thank you Photo Engineer , Autochrome uses RGB and when it is scanned , it makes flat histogram.
But when thinking ,
What about digital cameras , they use RGB pixels and by this way , they should aim to give flat histograms but this is not true.

Which is false ?

Best,

Umut

Mustafa Umut Sarac
04-30-2010, 10:27 PM
O.G. English is not my first language and may be yours too .
I installed Lightroom and opened my Zeiss Sony camera files , there were lots of mountains and colors at the histogram.
But when it comes to autochromes - landscape , city , forest - The histogram was single gray , horizontal and low profile. It is very interesting.

Best ,

Umut

Q.G.
04-30-2010, 10:40 PM
Can you post a link to one of those Autochromes on the web?

Histograms do not have to be flat, no.
They have to be a good representation of the distribution and frequency of tones in the scene that was captured in the image the histograms are statistics of.
They also show whether good use is made of the full range the capturing medium is capable of. If all tones are bunched up at one side (i.e. the range is not used fully), you can perform a histogram equalization, or redistribute tones over the entire range in another way, but that rarely leads to better pictures.

So if the Autochrome histograms are flat, either something strange is going on with the Autochromes themselves, or with the scan that was made of these, or with the software that produced the histogram.

2F/2F
04-30-2010, 10:40 PM
What is a "histogram"? I am sure someone at Hybrid Photo dot com knows!

Q.G.
04-30-2010, 10:50 PM
It is a statistical way of analyzing image content.
The data gathering can be performed using thingies like densitometers.

I doubt that using densitometers and thinking about tones in an image is off-topic in APUG.
Do you think it is?

Mustafa Umut Sarac
04-30-2010, 10:56 PM
http://3.bp.blogspot.com/_l5YNpRMm2eA/S9uXgMiZ5xI/AAAAAAAAAH8/q4u4H6wOpPw/s1600/n798612784_1046289_8913.jpg

I had been recorded many images but they were wide angle forest and city pictures.
I dont know this image has told quality but let me post it , this image comes from same family but its too dark.

Umut

Photo Engineer
04-30-2010, 10:58 PM
Thank you Photo Engineer , Autochrome uses RGB and when it is scanned , it makes flat histogram.
But when thinking ,
What about digital cameras , they use RGB pixels and by this way , they should aim to give flat histograms but this is not true.

Which is false ?

Best,

Umut

When scanned, digital data is sending the fact that it is RGB. Analog data is sending the fact that it is CMY (K). I think that the information transmitted may be critical.

PE

Q.G.
04-30-2010, 11:17 PM
The histogram(s) of that image aren't flat when i look at it/them.

nick mulder
04-30-2010, 11:57 PM
Hang on - what are you (we, possibly) attempting to compare here ?

The histogram from one digital representation of a scanned image to a digital camera originated image of what I'm assuming is another another scene ??

Mustafa Umut Sarac
05-01-2010, 12:40 AM
yes , histogram of this image is not flat but the lost ones had have . I will try to find at net again
This is not new invention least 3 months old.

Q.G.
05-01-2010, 05:38 AM
Hang on - what are you (we, possibly) attempting to compare here ?

The histogram from one digital representation of a scanned image to a digital camera originated image of what I'm assuming is another another scene ??

I think we are trying to figure out whether being an Autochrome does something special to the distribution of tones.

One thing to establish before we start thinking about that is indeed whether there is something special about that, i.e. whether histograms of representations of Autochromes indeed would/could differ from histograms of represenations of other images.
If so, there is a possibility that such a difference could (!) be due to the nature of Autochromes. If not, there's nothing to think about.

Q.G.
05-01-2010, 05:44 AM
yes , histogram of this image is not flat but the lost ones had have . I will try to find at net again
This is not new invention least 3 months old.

I have been looking on the net too, and as yet have not come across an Autochrome that has a flat line histogram.

Mustafa Umut Sarac
05-01-2010, 07:36 AM
I am sure whatever I saw but not a proof at hand at this moment.
I think We can reverse engineer the situation. What is the meaning of flat histogram , what kind of a image have a flat histogram. I am an Crossfield 656 Drum Scanner operator , have been printed 100 000 color negatives and been a service man for Heidelberg Newspaper machines , used many Leitz products and a thinker on classical paintings and the Leica relation for 15 years.

Q.G.
05-01-2010, 07:46 AM
Flat histograms indicate that each tone in the range that the image could contain occurs equally often as any other tone.
A continuous wedge would give such a tone frequency distribution.
Or a scene in which the tones are distributed in another pattern (preferably one that represents a thing in real life), yet by some magic all appear as often as any other tone. Could happen though. But repeatedly, in different images of different scenes???

Add in colour and consider that to have a flat line overall histogram, the histograms of all colour channels involved would also need to be flat, and it becomes even more difficult to imagine.

Mustafa Umut Sarac
05-01-2010, 08:48 AM
QC , Lets continiue to reverse engineering. May be We can post process an image as you told and see the result. This is called histogram matching or something similar to it .
Is there anyone who knows how to create such a histogram on a image or do I need to ask to hybrid photo ? This is not digital photography but get help from a calculator.