Does Contrast equate to sharpness?

[jurne12]

I'm doing a physics experiment for a paper I'm writing, but I need to figure out a way to measure the sharpness of a photograph. So, I figured that I could measure the contrast and have that be a stand in for sharpness, since I'm basically just observing how one thing affects image sharpness. So would that work? Is there any other way to measure sharpness?

thanks in advanced!!!

[pschlute]

Although contrast does have a major effect on sharpness of an image it is not the only one. An un-sharp image may still have high contrast ! It is a long time since I did physics but I think your approach is flawed.

[xpatUSA]

I'm doing a physics experiment for a paper I'm writing, but I need to figure out a way to measure the sharpness of a photograph. So, I figured that I could measure the contrast and have that be a stand in for sharpness, since I'm basically just observing how one thing affects image sharpness. So would that work? Is there any other way to measure sharpness?

Title question is too vague, sorry.

"sharpness" and "contrast" are both subjective words which mean many things to many men and have many defined units and methods of measurement. This paper could get you started:

http://www.falklumo.com/lumolabs/art...ess/index.html

Also search on "Norman Koren" or "Bob Atkins" plus the term "MTF" ...

If you are creating the image, you could shoot a sharp straight edge inclined at about 5 degrees and measure the Edge Spread Response using available apps like QuickMTF, Imatest, ImageJ, etc. Your metric will be the 10-90% rise with units of px. The spatial frequency at which MTF = 50% aka MTF50 is also a popular measure.

Some example plots here ...

https://www.dpreview.com/forums/post/63954294

Or shoot a Siemens Star, preferable the sinusoidal type, and measure the diameter of the non-blurred spokes.

A target with both a Siemens Star and two slant edges here:

http://kronometric.org/phot/iq/res/JTF144_noCenter.png

Some sharpness stuff on my site here:

http://kronometric.org/phot/iq/sharpness/

I would avoid Acutance and Subjective Quality Factor because they involve the variables of human visual response and viewing distance.

Alternatively, for someone else's image, use wavelet processing to split the image into levels of detail and observe a histogram at the smaller levels e.g. 1px, 2px, 4px, ... the greater the standard deviation, the more the contrast - and contrast at lower detail levels (aka micro-contrast) is indicative of "sharpness".

[William W]

I'm doing a physics experiment for a paper I'm writing . . .

Perhaps you might tell us the parameters of the paper and the intended readership and audience: "a paper" can mean many things, from an High School project to a Doctorial Thesis.

More interesting is the embedded link (which, by the way didn't quite work) that is in your Opening Post: embedded links to unrelated subjects which are encased in the opening thread of a first time poster always raise my suspicion that the poster is spamming.

Perhaps you might like to comment - or explain?

WW

[xpatUSA]

More interesting is the embedded link (which, by the way didn't quite work)

[edit] Or maybe it did LOL [/edit]

that is in your Opening Post: embedded links to unrelated subjects which are encased in the opening thread of a first time poster always raise my suspicion that the poster is spamming.

Perhaps you might like to comment - or explain?

WW

Very well spotted, Bill!!

It's a link to a download page for something called "WhatsApp APK". First hit up in Google says "May 5, 2020 ... YoWhatsApp is a famous application that is known for its amazing features all over the world. This is a modified version of WhatsApp. ..."

Suspicious as Hell, eh? I refrained from clicking on it, functional or not.

I may have wasted my time above ...

[William W]

. . . I may have wasted my time above ...

Nope.

I am busily reading the links that you provided - there is always something new to learn.

Bill

[Manfred M]

Let's see if the poster is back.

I too am suspicious when I see a link to something quite unrelated to the question buried in the post. I suspect this might be a phishing expedition that has failed...

[xpatUSA]

Let's see if the poster is back.

I too am suspicious when I see a link to something quite unrelated to the question buried in the post. I suspect this might be a phishing expedition that has failed...

The link is to a messaging service "YoWhatsApp" which was originated in India. It is based on the original American "WhatsApp" which per se is banned in quite a few countries. YoWhatsApp seems genuine enough but the OP had no reason to link to it in a post especially via a Smiley. So, I doubt we'll see a response by the OP ...

[Manfred M]

The link is to a messaging service "YoWhatsApp" which was originated in India. It is based on the original American "WhatsApp" which per se is banned in quite a few countries. YoWhatsApp seems genuine enough but the OP had no reason to link to it in a post especially via a Smiley. So, I doubt we'll see a response by the OP ...

I did check things out before I modified the post and noticed that. WhatApp is extremely popular throughout India and I found it was necessary to have it on my phone when we visited there. There was no other way to stay in touch with the groups I was involved with.

On the other hand, we don't know if this app comes with extra "goodies" that we wouldn't want on our phones...

[William W]

I did check things out before I modified the post and noticed that.

Thanks, I was rushed last night and anticipated that you'd read my post which was a warning others.

You did read it before I came back to CiC just to send you a PM - so I went to sleep instead!

Bill

[davidedric]

I read a very similarly worded post elsewhere (probably dpr) a few weeks ago. I'm with the sceptics, but ready to be proved wrong, again

[Astro]

I may have wasted my time above ...

Not in my case, Like Bill I'm very interested in your links ...

[xpatUSA]

Not in my case, Like Bill I'm very interested in your links ...

Thanks both,

I guess @jurne12 is busy on his paper ... LOL

[DanK]

I doubt we will hear from this person again. The post read like one of the many from students who find it easier to post on a forum than to look something up and read.