Autochrome Histogram - Suprise for me

[Mustafa Umut Sarac]

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]

Sounds like an artifact of post processing after the images were scanned.

[Mustafa Umut Sarac]

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]

It may reflect an additive system vs a subtractive system.

PE

[Q.G.]

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]

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]

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.]

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]

What is a "histogram"? I am sure someone at Hybrid Photo dot com knows!

[Q.G.]

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?