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How to determine the actual or “true” resolution of a digital photograph?


How to analyze images with Fast Fourier Transform method?Why are effective pixels greater than the actual resolution?how do you determine the size of an image based on resolution , ppi, and type?How can a high resolution camera matter when the output is low resolution?How to scale down images in Lightroom while maintaining quality?What is Snapsort's “true resolution” score?Should two identical digital pictures of the same resolution and format have the same size?How to take high resolution pictures?What size and resolution should I make digital files that I am selling to clients?How can I automatically downsize images which have more pixels than needed for the actual resolution?does the presence of Moiré in a photo implies the “lens outresolve the sensor”?






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}







2















What I mean by "true" resolution is the resolution at which the maximum available amount of real detail is present. For an ideal picture this resolution is the same as the resolution encoded in the image file. However, in other cases the actual true resolution may be less than the resolution of the image file:




  1. If the image file was digitally scaled - for instance, if the camera has a "digital zoom" feature where it upsamples the individual pixels.


  2. If the image is not completely sharp and in focus.



In either of these cases, it is useful to me to have some mechanical method of identifying what the actual true resolution of the image is independent of what the image file says. How can I do this? Is there some software or algorithm which can take an image and analyze it and tell me the highest resolution it can be displayed at while showing detail at the resolution?



My initial naive expectation that it should be "obvious" and easy to determine by some simple mechanism such as compressed sizes is thwarted in cases where the upscaled image has noticable artifacting or noise not present in the original.










share|improve this question


















  • 1





    I'm voting to close this question as off-topic because it seems to be a theoretical question without any true photographic application.

    – Philip Kendall
    2 hours ago






  • 1





    The question of, "Is this cropped from a larger picture?" comes up all the time in photography. The fact that it can't be reliably determined is an important point and very much on-topic.

    – user10216038
    1 hour ago






  • 1





    @user10216038 whether or not something is cropped may be of use in making a photograph, but I’m failing to see the importance after the fact. If it’s a good clean photo, who cares if it was cropped to obtain the final composition? Isn’t that the advantage of high res sensors?

    – Hueco
    39 mins ago











  • @Hueco from a purely hypothetical standpoint, an example of "who cares" might be a judge/panel for a photo contest who requires images to not be cropped (for some strange reason). Also, off the top of my head, perhaps some sort of detection of whether an image is modified (for journalistic submission purposes). I'm not weighing in on the topicality of this question, just devilishly advocating conceivable reasons to care.

    – scottbb
    15 mins ago











  • This question assumes that OOF areas do not contribute to “true resolution”. Is a panned motion blur shot not “true”? How about a blurred photo shot through wet glass? What problem are you actually trying to solve?

    – Hueco
    38 secs ago


















2















What I mean by "true" resolution is the resolution at which the maximum available amount of real detail is present. For an ideal picture this resolution is the same as the resolution encoded in the image file. However, in other cases the actual true resolution may be less than the resolution of the image file:




  1. If the image file was digitally scaled - for instance, if the camera has a "digital zoom" feature where it upsamples the individual pixels.


  2. If the image is not completely sharp and in focus.



In either of these cases, it is useful to me to have some mechanical method of identifying what the actual true resolution of the image is independent of what the image file says. How can I do this? Is there some software or algorithm which can take an image and analyze it and tell me the highest resolution it can be displayed at while showing detail at the resolution?



My initial naive expectation that it should be "obvious" and easy to determine by some simple mechanism such as compressed sizes is thwarted in cases where the upscaled image has noticable artifacting or noise not present in the original.










share|improve this question


















  • 1





    I'm voting to close this question as off-topic because it seems to be a theoretical question without any true photographic application.

    – Philip Kendall
    2 hours ago






  • 1





    The question of, "Is this cropped from a larger picture?" comes up all the time in photography. The fact that it can't be reliably determined is an important point and very much on-topic.

    – user10216038
    1 hour ago






  • 1





    @user10216038 whether or not something is cropped may be of use in making a photograph, but I’m failing to see the importance after the fact. If it’s a good clean photo, who cares if it was cropped to obtain the final composition? Isn’t that the advantage of high res sensors?

    – Hueco
    39 mins ago











  • @Hueco from a purely hypothetical standpoint, an example of "who cares" might be a judge/panel for a photo contest who requires images to not be cropped (for some strange reason). Also, off the top of my head, perhaps some sort of detection of whether an image is modified (for journalistic submission purposes). I'm not weighing in on the topicality of this question, just devilishly advocating conceivable reasons to care.

    – scottbb
    15 mins ago











  • This question assumes that OOF areas do not contribute to “true resolution”. Is a panned motion blur shot not “true”? How about a blurred photo shot through wet glass? What problem are you actually trying to solve?

    – Hueco
    38 secs ago














2












2








2








What I mean by "true" resolution is the resolution at which the maximum available amount of real detail is present. For an ideal picture this resolution is the same as the resolution encoded in the image file. However, in other cases the actual true resolution may be less than the resolution of the image file:




  1. If the image file was digitally scaled - for instance, if the camera has a "digital zoom" feature where it upsamples the individual pixels.


  2. If the image is not completely sharp and in focus.



In either of these cases, it is useful to me to have some mechanical method of identifying what the actual true resolution of the image is independent of what the image file says. How can I do this? Is there some software or algorithm which can take an image and analyze it and tell me the highest resolution it can be displayed at while showing detail at the resolution?



My initial naive expectation that it should be "obvious" and easy to determine by some simple mechanism such as compressed sizes is thwarted in cases where the upscaled image has noticable artifacting or noise not present in the original.










share|improve this question














What I mean by "true" resolution is the resolution at which the maximum available amount of real detail is present. For an ideal picture this resolution is the same as the resolution encoded in the image file. However, in other cases the actual true resolution may be less than the resolution of the image file:




  1. If the image file was digitally scaled - for instance, if the camera has a "digital zoom" feature where it upsamples the individual pixels.


  2. If the image is not completely sharp and in focus.



In either of these cases, it is useful to me to have some mechanical method of identifying what the actual true resolution of the image is independent of what the image file says. How can I do this? Is there some software or algorithm which can take an image and analyze it and tell me the highest resolution it can be displayed at while showing detail at the resolution?



My initial naive expectation that it should be "obvious" and easy to determine by some simple mechanism such as compressed sizes is thwarted in cases where the upscaled image has noticable artifacting or noise not present in the original.







resolution






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked 2 hours ago









MichaelMichael

161129




161129








  • 1





    I'm voting to close this question as off-topic because it seems to be a theoretical question without any true photographic application.

    – Philip Kendall
    2 hours ago






  • 1





    The question of, "Is this cropped from a larger picture?" comes up all the time in photography. The fact that it can't be reliably determined is an important point and very much on-topic.

    – user10216038
    1 hour ago






  • 1





    @user10216038 whether or not something is cropped may be of use in making a photograph, but I’m failing to see the importance after the fact. If it’s a good clean photo, who cares if it was cropped to obtain the final composition? Isn’t that the advantage of high res sensors?

    – Hueco
    39 mins ago











  • @Hueco from a purely hypothetical standpoint, an example of "who cares" might be a judge/panel for a photo contest who requires images to not be cropped (for some strange reason). Also, off the top of my head, perhaps some sort of detection of whether an image is modified (for journalistic submission purposes). I'm not weighing in on the topicality of this question, just devilishly advocating conceivable reasons to care.

    – scottbb
    15 mins ago











  • This question assumes that OOF areas do not contribute to “true resolution”. Is a panned motion blur shot not “true”? How about a blurred photo shot through wet glass? What problem are you actually trying to solve?

    – Hueco
    38 secs ago














  • 1





    I'm voting to close this question as off-topic because it seems to be a theoretical question without any true photographic application.

    – Philip Kendall
    2 hours ago






  • 1





    The question of, "Is this cropped from a larger picture?" comes up all the time in photography. The fact that it can't be reliably determined is an important point and very much on-topic.

    – user10216038
    1 hour ago






  • 1





    @user10216038 whether or not something is cropped may be of use in making a photograph, but I’m failing to see the importance after the fact. If it’s a good clean photo, who cares if it was cropped to obtain the final composition? Isn’t that the advantage of high res sensors?

    – Hueco
    39 mins ago











  • @Hueco from a purely hypothetical standpoint, an example of "who cares" might be a judge/panel for a photo contest who requires images to not be cropped (for some strange reason). Also, off the top of my head, perhaps some sort of detection of whether an image is modified (for journalistic submission purposes). I'm not weighing in on the topicality of this question, just devilishly advocating conceivable reasons to care.

    – scottbb
    15 mins ago











  • This question assumes that OOF areas do not contribute to “true resolution”. Is a panned motion blur shot not “true”? How about a blurred photo shot through wet glass? What problem are you actually trying to solve?

    – Hueco
    38 secs ago








1




1





I'm voting to close this question as off-topic because it seems to be a theoretical question without any true photographic application.

– Philip Kendall
2 hours ago





I'm voting to close this question as off-topic because it seems to be a theoretical question without any true photographic application.

– Philip Kendall
2 hours ago




1




1





The question of, "Is this cropped from a larger picture?" comes up all the time in photography. The fact that it can't be reliably determined is an important point and very much on-topic.

– user10216038
1 hour ago





The question of, "Is this cropped from a larger picture?" comes up all the time in photography. The fact that it can't be reliably determined is an important point and very much on-topic.

– user10216038
1 hour ago




1




1





@user10216038 whether or not something is cropped may be of use in making a photograph, but I’m failing to see the importance after the fact. If it’s a good clean photo, who cares if it was cropped to obtain the final composition? Isn’t that the advantage of high res sensors?

– Hueco
39 mins ago





@user10216038 whether or not something is cropped may be of use in making a photograph, but I’m failing to see the importance after the fact. If it’s a good clean photo, who cares if it was cropped to obtain the final composition? Isn’t that the advantage of high res sensors?

– Hueco
39 mins ago













@Hueco from a purely hypothetical standpoint, an example of "who cares" might be a judge/panel for a photo contest who requires images to not be cropped (for some strange reason). Also, off the top of my head, perhaps some sort of detection of whether an image is modified (for journalistic submission purposes). I'm not weighing in on the topicality of this question, just devilishly advocating conceivable reasons to care.

– scottbb
15 mins ago





@Hueco from a purely hypothetical standpoint, an example of "who cares" might be a judge/panel for a photo contest who requires images to not be cropped (for some strange reason). Also, off the top of my head, perhaps some sort of detection of whether an image is modified (for journalistic submission purposes). I'm not weighing in on the topicality of this question, just devilishly advocating conceivable reasons to care.

– scottbb
15 mins ago













This question assumes that OOF areas do not contribute to “true resolution”. Is a panned motion blur shot not “true”? How about a blurred photo shot through wet glass? What problem are you actually trying to solve?

– Hueco
38 secs ago





This question assumes that OOF areas do not contribute to “true resolution”. Is a panned motion blur shot not “true”? How about a blurred photo shot through wet glass? What problem are you actually trying to solve?

– Hueco
38 secs ago










3 Answers
3






active

oldest

votes


















2














You could compute the Fourier transform of the picture and analyze it in frequency space. If the image was upsampled, higher frequencies will be missing in the transformed image.



Note that the absence of the high frequencies could also mean that the original image did not contain enough detail, or it was not sharp in the first place.



Related: How to analyze images with Fast Fourier Transform method?






share|improve this answer

































    1














    Assuming accurate meta data (EXIF) is present, it would be possible to determine possible camera model resolutions.



    Without metadata it's a statistical guess from common available possibilities.



    What you refer to as "True Resolution" is a difficult concept. To start with, digital cameras don't have pixels in the first place, they have sensors. The sensors in turn are processed to produce pixels, but many sensors produce one pixel and one sensor is part of many pixels.



    There are image analysis/forensic tools for determining things like edited, cloned, recompressed, resized, and other alterations. Sometimes the JPG cosine compression tables or noise patterns can strongly indicate a particular camera.



    In general, unless you can establish the camera model, I don't believe you can realistically get what you want.






    share|improve this answer































      0















      What I mean by "true" resolution is the resolution at which the maximum available amount of real detail is present. For an ideal picture this resolution is the same as the resolution encoded in the image file.




      To put that another way, you're trying to differentiate images where one pixel represents one pixel on the camera sensor (i.e., a 100% crop) from those that don't. So a shot taken with a full-frame lens on a full-frame SLR would be considered "true," as would one taken with a cropped-frame lens and cropped to just show what was in the image circle.




      In either of these cases, it is useful to me to have some mechanical method of identifying what the actual true resolution of the image is independent of what the image file says. How can I do this?




      Most cameras with digital zoom provide the DigitalZoomRatio EXIF tag which will tell you when scaling happened in-camera. You will not, of course, be able to tell if the image was scaled elsewhere or the metadata was tampered with unless you have some way to verify that the image and metadata were actually produced by the camera.



      Assuming you trust the metadata, the ration could be sued to figure out that a 6000x4000 image that had a zoom ratio of 2.0 started life as 3000x2000. That doesn't mean the image can be scaled back down to that size and all will be well; any changes made during upscaling would have an effect on the downscaled version.



      You can't do anything with the not-completely-sharp case for the simple reason that given just the image, there's no source of ground truth for what light fell on the sensor and no insight into the photographer's intent. Shooting with intentionally-small depth of field, putting a diffusing filter in front of the lens, producing motion blur or intentionally shooting out of focus would be captured at the camera's "true" resolution. Any algorithm trying to root out scaling would produce a wrong result.



      The best you can do is read the metadata and decide whether or not you trust it.






      share|improve this answer
























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        3 Answers
        3






        active

        oldest

        votes








        3 Answers
        3






        active

        oldest

        votes









        active

        oldest

        votes






        active

        oldest

        votes









        2














        You could compute the Fourier transform of the picture and analyze it in frequency space. If the image was upsampled, higher frequencies will be missing in the transformed image.



        Note that the absence of the high frequencies could also mean that the original image did not contain enough detail, or it was not sharp in the first place.



        Related: How to analyze images with Fast Fourier Transform method?






        share|improve this answer






























          2














          You could compute the Fourier transform of the picture and analyze it in frequency space. If the image was upsampled, higher frequencies will be missing in the transformed image.



          Note that the absence of the high frequencies could also mean that the original image did not contain enough detail, or it was not sharp in the first place.



          Related: How to analyze images with Fast Fourier Transform method?






          share|improve this answer




























            2












            2








            2







            You could compute the Fourier transform of the picture and analyze it in frequency space. If the image was upsampled, higher frequencies will be missing in the transformed image.



            Note that the absence of the high frequencies could also mean that the original image did not contain enough detail, or it was not sharp in the first place.



            Related: How to analyze images with Fast Fourier Transform method?






            share|improve this answer















            You could compute the Fourier transform of the picture and analyze it in frequency space. If the image was upsampled, higher frequencies will be missing in the transformed image.



            Note that the absence of the high frequencies could also mean that the original image did not contain enough detail, or it was not sharp in the first place.



            Related: How to analyze images with Fast Fourier Transform method?







            share|improve this answer














            share|improve this answer



            share|improve this answer








            edited 1 hour ago

























            answered 1 hour ago









            boglbogl

            39138




            39138

























                1














                Assuming accurate meta data (EXIF) is present, it would be possible to determine possible camera model resolutions.



                Without metadata it's a statistical guess from common available possibilities.



                What you refer to as "True Resolution" is a difficult concept. To start with, digital cameras don't have pixels in the first place, they have sensors. The sensors in turn are processed to produce pixels, but many sensors produce one pixel and one sensor is part of many pixels.



                There are image analysis/forensic tools for determining things like edited, cloned, recompressed, resized, and other alterations. Sometimes the JPG cosine compression tables or noise patterns can strongly indicate a particular camera.



                In general, unless you can establish the camera model, I don't believe you can realistically get what you want.






                share|improve this answer




























                  1














                  Assuming accurate meta data (EXIF) is present, it would be possible to determine possible camera model resolutions.



                  Without metadata it's a statistical guess from common available possibilities.



                  What you refer to as "True Resolution" is a difficult concept. To start with, digital cameras don't have pixels in the first place, they have sensors. The sensors in turn are processed to produce pixels, but many sensors produce one pixel and one sensor is part of many pixels.



                  There are image analysis/forensic tools for determining things like edited, cloned, recompressed, resized, and other alterations. Sometimes the JPG cosine compression tables or noise patterns can strongly indicate a particular camera.



                  In general, unless you can establish the camera model, I don't believe you can realistically get what you want.






                  share|improve this answer


























                    1












                    1








                    1







                    Assuming accurate meta data (EXIF) is present, it would be possible to determine possible camera model resolutions.



                    Without metadata it's a statistical guess from common available possibilities.



                    What you refer to as "True Resolution" is a difficult concept. To start with, digital cameras don't have pixels in the first place, they have sensors. The sensors in turn are processed to produce pixels, but many sensors produce one pixel and one sensor is part of many pixels.



                    There are image analysis/forensic tools for determining things like edited, cloned, recompressed, resized, and other alterations. Sometimes the JPG cosine compression tables or noise patterns can strongly indicate a particular camera.



                    In general, unless you can establish the camera model, I don't believe you can realistically get what you want.






                    share|improve this answer













                    Assuming accurate meta data (EXIF) is present, it would be possible to determine possible camera model resolutions.



                    Without metadata it's a statistical guess from common available possibilities.



                    What you refer to as "True Resolution" is a difficult concept. To start with, digital cameras don't have pixels in the first place, they have sensors. The sensors in turn are processed to produce pixels, but many sensors produce one pixel and one sensor is part of many pixels.



                    There are image analysis/forensic tools for determining things like edited, cloned, recompressed, resized, and other alterations. Sometimes the JPG cosine compression tables or noise patterns can strongly indicate a particular camera.



                    In general, unless you can establish the camera model, I don't believe you can realistically get what you want.







                    share|improve this answer












                    share|improve this answer



                    share|improve this answer










                    answered 1 hour ago









                    user10216038user10216038

                    3315




                    3315























                        0















                        What I mean by "true" resolution is the resolution at which the maximum available amount of real detail is present. For an ideal picture this resolution is the same as the resolution encoded in the image file.




                        To put that another way, you're trying to differentiate images where one pixel represents one pixel on the camera sensor (i.e., a 100% crop) from those that don't. So a shot taken with a full-frame lens on a full-frame SLR would be considered "true," as would one taken with a cropped-frame lens and cropped to just show what was in the image circle.




                        In either of these cases, it is useful to me to have some mechanical method of identifying what the actual true resolution of the image is independent of what the image file says. How can I do this?




                        Most cameras with digital zoom provide the DigitalZoomRatio EXIF tag which will tell you when scaling happened in-camera. You will not, of course, be able to tell if the image was scaled elsewhere or the metadata was tampered with unless you have some way to verify that the image and metadata were actually produced by the camera.



                        Assuming you trust the metadata, the ration could be sued to figure out that a 6000x4000 image that had a zoom ratio of 2.0 started life as 3000x2000. That doesn't mean the image can be scaled back down to that size and all will be well; any changes made during upscaling would have an effect on the downscaled version.



                        You can't do anything with the not-completely-sharp case for the simple reason that given just the image, there's no source of ground truth for what light fell on the sensor and no insight into the photographer's intent. Shooting with intentionally-small depth of field, putting a diffusing filter in front of the lens, producing motion blur or intentionally shooting out of focus would be captured at the camera's "true" resolution. Any algorithm trying to root out scaling would produce a wrong result.



                        The best you can do is read the metadata and decide whether or not you trust it.






                        share|improve this answer




























                          0















                          What I mean by "true" resolution is the resolution at which the maximum available amount of real detail is present. For an ideal picture this resolution is the same as the resolution encoded in the image file.




                          To put that another way, you're trying to differentiate images where one pixel represents one pixel on the camera sensor (i.e., a 100% crop) from those that don't. So a shot taken with a full-frame lens on a full-frame SLR would be considered "true," as would one taken with a cropped-frame lens and cropped to just show what was in the image circle.




                          In either of these cases, it is useful to me to have some mechanical method of identifying what the actual true resolution of the image is independent of what the image file says. How can I do this?




                          Most cameras with digital zoom provide the DigitalZoomRatio EXIF tag which will tell you when scaling happened in-camera. You will not, of course, be able to tell if the image was scaled elsewhere or the metadata was tampered with unless you have some way to verify that the image and metadata were actually produced by the camera.



                          Assuming you trust the metadata, the ration could be sued to figure out that a 6000x4000 image that had a zoom ratio of 2.0 started life as 3000x2000. That doesn't mean the image can be scaled back down to that size and all will be well; any changes made during upscaling would have an effect on the downscaled version.



                          You can't do anything with the not-completely-sharp case for the simple reason that given just the image, there's no source of ground truth for what light fell on the sensor and no insight into the photographer's intent. Shooting with intentionally-small depth of field, putting a diffusing filter in front of the lens, producing motion blur or intentionally shooting out of focus would be captured at the camera's "true" resolution. Any algorithm trying to root out scaling would produce a wrong result.



                          The best you can do is read the metadata and decide whether or not you trust it.






                          share|improve this answer


























                            0












                            0








                            0








                            What I mean by "true" resolution is the resolution at which the maximum available amount of real detail is present. For an ideal picture this resolution is the same as the resolution encoded in the image file.




                            To put that another way, you're trying to differentiate images where one pixel represents one pixel on the camera sensor (i.e., a 100% crop) from those that don't. So a shot taken with a full-frame lens on a full-frame SLR would be considered "true," as would one taken with a cropped-frame lens and cropped to just show what was in the image circle.




                            In either of these cases, it is useful to me to have some mechanical method of identifying what the actual true resolution of the image is independent of what the image file says. How can I do this?




                            Most cameras with digital zoom provide the DigitalZoomRatio EXIF tag which will tell you when scaling happened in-camera. You will not, of course, be able to tell if the image was scaled elsewhere or the metadata was tampered with unless you have some way to verify that the image and metadata were actually produced by the camera.



                            Assuming you trust the metadata, the ration could be sued to figure out that a 6000x4000 image that had a zoom ratio of 2.0 started life as 3000x2000. That doesn't mean the image can be scaled back down to that size and all will be well; any changes made during upscaling would have an effect on the downscaled version.



                            You can't do anything with the not-completely-sharp case for the simple reason that given just the image, there's no source of ground truth for what light fell on the sensor and no insight into the photographer's intent. Shooting with intentionally-small depth of field, putting a diffusing filter in front of the lens, producing motion blur or intentionally shooting out of focus would be captured at the camera's "true" resolution. Any algorithm trying to root out scaling would produce a wrong result.



                            The best you can do is read the metadata and decide whether or not you trust it.






                            share|improve this answer














                            What I mean by "true" resolution is the resolution at which the maximum available amount of real detail is present. For an ideal picture this resolution is the same as the resolution encoded in the image file.




                            To put that another way, you're trying to differentiate images where one pixel represents one pixel on the camera sensor (i.e., a 100% crop) from those that don't. So a shot taken with a full-frame lens on a full-frame SLR would be considered "true," as would one taken with a cropped-frame lens and cropped to just show what was in the image circle.




                            In either of these cases, it is useful to me to have some mechanical method of identifying what the actual true resolution of the image is independent of what the image file says. How can I do this?




                            Most cameras with digital zoom provide the DigitalZoomRatio EXIF tag which will tell you when scaling happened in-camera. You will not, of course, be able to tell if the image was scaled elsewhere or the metadata was tampered with unless you have some way to verify that the image and metadata were actually produced by the camera.



                            Assuming you trust the metadata, the ration could be sued to figure out that a 6000x4000 image that had a zoom ratio of 2.0 started life as 3000x2000. That doesn't mean the image can be scaled back down to that size and all will be well; any changes made during upscaling would have an effect on the downscaled version.



                            You can't do anything with the not-completely-sharp case for the simple reason that given just the image, there's no source of ground truth for what light fell on the sensor and no insight into the photographer's intent. Shooting with intentionally-small depth of field, putting a diffusing filter in front of the lens, producing motion blur or intentionally shooting out of focus would be captured at the camera's "true" resolution. Any algorithm trying to root out scaling would produce a wrong result.



                            The best you can do is read the metadata and decide whether or not you trust it.







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                            answered 1 hour ago









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