Histograms

Sally · #1 01-03-2002, 06:36 PM

Histograms.

Why does the histogram change on a photo posted to this site?

Is it to prevent the photo being used commercially?

That would be a good reason.

Here is an example of one posted by me and below it, the same image down loaded

Sally

DJ Dubovsky · #2 01-03-2002, 06:55 PM

Sally
Clarification: Do you mean the histogram of your original is the first one and the second one is a histogram of your photo after you submitted it to this site and downloaded it again?
Never realized that before so it's all new to me.
DJ

Doug Nelson · #3 01-03-2002, 07:57 PM

Make sure you're comparing the jpg that was submitted, and not your original work file. Let me know which challenge this was for and I'll look into it.

Sally · #4 01-03-2002, 08:37 PM

This wasn't a challenge, I no longer do them because of this problem.

I have enclosed a copy of both pics with their histograms with this posting.

Sally

Ed_L · #5 01-03-2002, 09:09 PM

Sally,

I'm not sure I understand you. Are you saying that the histogram changes simply from sending it in? Or does it change *after* you change the image size and save to jpg?

Ed

Sally · #6 01-03-2002, 11:43 PM

Yes I’ve got that histogram with every image I've down loaded from this site, with one exception.

I haven’t looked at a lot of the site because we have a very slow connection.

Sally

CJ Swartz · #7 01-04-2002, 12:04 AM

Sally,

IF you're saying that the histogram is different when you download the same file that you uploaded to this website, to the extent of getting the "comb" effect -- that does not happen when I download files from here.

This may be a case for Mr. RetouchPRO himself.

Sally · #8 01-04-2002, 12:35 AM

Yes CJ, that is exactly what I'm saying. Perhaps it is because I have PC and not a mac. Sally

Doug Nelson · #9 01-04-2002, 05:08 AM

I'm a bit at a loss here. If it's not part of a Challenge, where are the pictures uploaded to be viewed? As attachments? The Archives?

I'm feeling kind of dumb here, lend me a hand.

Sally · #10 01-04-2002, 06:16 AM

Sorry for the confusion.

I wrote a piece on scanning textured originals and included a close up of a before and after.

Some one asked me to show the whole photo restored. By mistake I posted it in the “spots, I can't get the spots out” thread.

From this attachment I down loaded my own image. That is how I was able to demonstrate the different histograms.

I hope this is clearer and not more confusing.

Sally

Doug Nelson · #11 01-04-2002, 06:26 AM

As a test, I made up an under 100k jpg of a typical pre-restoration image. I made a histogram of that jpg. Then I uploaded the image jpg and viewed it. Then I saved it (not via copy) and ran another histogram. Attached are my results.

Sally · #12 01-04-2002, 06:33 AM

What a mystery.

Do you have mac or pc?

It's 9.30pm here what time is it there?
Are you up all night?

Sally

Doug Nelson · #13 01-04-2002, 06:38 AM

I use a PC, though I can't imagine how that could make a difference. There is no mechanism to change the file during or after uploading, or during downloading. If anything did get changed, the file would be corrupted and unviewable. It's a straight binary transfer.

It's about 7:30am here. I keep "irregular" hours

DJ Dubovsky · #14 01-04-2002, 08:58 AM

We have a real mystery here Sally. Actually the histogram that is shown on the second example shouldn't have much of an image left to view with all the holes in it, I would think.
DJ

john_opitz · #15 01-04-2002, 09:52 AM

What DJ said is true. That's why I don't rely on historgrams anymore. If I want to see what's going on in the image. I look in the channels itself. Being a curve user only. A lot of people that use levels that go to using curves would like to see a historgram with curves, like in using levels. But really, I would not worry, because what you see on the screen is what you see on the downloaded image is what counts(as in the downloaded images). I have that Dan Margulis attitude. Do you want good looking images or good looking historgrams. Even if your not into Dan Margulis, Katrin Eismann has it in her book as an example: page 47 and 48. The before and after images, the historgrams (one in 8 bit and the other in 16 bit) are the same. After changes done to it. The images look the same in 8 and 16 bit, but the historgrams are different.