Timeline for How to technically measure sharpness?
Current License: CC BY-SA 4.0
14 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jun 7, 2021 at 19:16 | comment | added | Laurent | @MichaelC I have opened another thread here: photo.stackexchange.com/questions/125089/… | |
| Jun 7, 2021 at 18:31 | comment | added | Laurent | @MichaelC I had another question, do you know a reliable MTF program that I could use? Imatest is really too expensive for and MTF mapper is really giving weird results compared to Imatest. Maybe there is something in between that would fit my need and budget. Thanks! | |
| Jun 7, 2021 at 18:30 | comment | added | Laurent | @MichaelC Thanks for your extensive comment. I did not rule out MTF, I even tried to reproduce it but I'm not yet there. I wanted to find something simpler for my blog as most of the people do not understand what MTF means. I know it's a bit like cutting corners but I'd like to come to a single score indicating how sharp a smartphone camera can be. I also know that it's sharper in the middle but again, most of normal smartphone users don't care about this. I think I'll create a specific thread about MTF to dig deeper into this. | |
| Jun 6, 2021 at 22:43 | comment | added | Michael C | Horizontal and vertical bars do not, strictly speaking, measure tangential and sagittal performance. Sagittal lines are like the spokes of a wheel spreading out from the center of the lens' field of view. Tangential lines are tangent to the circular surface of the wheel that rolls over the ground. | |
| Jun 6, 2021 at 22:36 | comment | added | Michael C | Do note that the accuracy of contrast (acutance - or sharpness) measurements is dependent upon the focus position of the camera/lens system. If the target is misfocused, the system will measure less sharp than when the lens is optimally focused. That's the most significant problem with testing systems such as camera phones, because focus often can't be set manually and then the distance between the camera and target altered in gradations of micrometers (µm) using a test bench to find the point of sharpest focus. | |
| Jun 6, 2021 at 22:30 | comment | added | Michael C | If the average of the dark areas is at 25% brightness and the average of the light areas is at 75% brightness, that results in a score of 0.50, because the average difference between the dark and light areas is 50% of total possible difference between pure black and pure white. At the resolution limit of the camera/lens system, both areas are equally bright or dark and thus can not be discriminated from each other. | |
| Jun 6, 2021 at 22:28 | comment | added | Michael C | @Larent It seems you're trying to reinvent the wheel that has been around and has already been optimized for a long, long time. MTF measurements and other methods used to measure acutance do not depend on the camera in question being a DSLR. They analyze the results (i.e. the photos produced) to determine numerical measurements. The entire contrast side of an MTF diagram is the scale that shows the percentage difference in brightness between the white and black lines. If the white line is fully white and the dark line is fully black, that's a 1.00 score (which never actually happens). | |
| Jun 6, 2021 at 18:46 | comment | added | Laurent | @user10216038 Thanks for the suggestion, I should have pointed out that I'm testing smartphone cameras which means that I can't run any software like for dslr? I need somehow to reverse engineer what the camera is measuring, compare with real life observation until the scripts produces something ok. | |
| Jun 6, 2021 at 18:43 | comment | added | Laurent | @MichaelC I have horizontal & vertical bars but as I'm looking at pixels values programmatically I take the easy route by measuring any deviation from the original white and black stripes | |
| Jun 6, 2021 at 15:57 | comment | added | user10216038 | Are you measuring lenses in the abstract without a camera? If not, the reality is that the camera will also affect your measurements to some degree. If you are using an auto focus camera and lens combination, you can save yourself a lot of wheel re-inventing by using existing products that already do this. One relatively inexpensive product I've used is Reikan FoCal focal-iq.com . If you're still determined to do it yourself, take a look at some of their analysis results like focal-iq.com/lenses/… | |
| Jun 6, 2021 at 14:02 | comment | added | Michael C | If you really want to do it right | |
| Jun 6, 2021 at 13:31 | comment | added | Michael C | Do you measure both tangentially and sagittally? Most lenses will differ slightly in each direction. Some lenses differ significantly between the two, especially near the edges and corners of the frame. | |
| Jun 6, 2021 at 11:46 | review | First posts | |||
| Jun 10, 2021 at 3:41 | |||||
| Jun 6, 2021 at 11:37 | history | asked | Laurent | CC BY-SA 4.0 |