Unfortunately you can't separate the technical and aesthetic properties. For example, you ask
" * Is the subject properly focused? > * Is the image sharp "enough"? > * Is the exposure "correct" / "optimal"? I.e. especially since I > use ETTR (expose-to-the-right): > * did I overexposed something, > * do I have underexposed areas, and like above how much, etc " And I ask in return what does "properly focused" mean? It depends on what you intend for the picture, so it cannot have a single once-and-for-all answer - you have to make a subjective, aesthetic judgement. "Sharp enough" for what? What is "correct" exposure? These questions have no meaning on their own, divorced from the subject matter of the photograph, and the intentions of the photographer. The technical properties are there to serve you, they have no independent meaning. In taking the picture your intention is to communicate something as effectively as you can for your purposes to your intended audience. So choosing between similar pictures with different technical properties is not something that can be done independently of your personal judgement and priorities. So in answer to question A, you have to decide for yourself. In one of your examples, you said sharpness, presumably meaning least camera shake, but it may be different in other circumstances. And to answer question B: your brain, your eyes and your discernment. Some of the most aesthetically successful pictures are so because of, not despite, their technical 'faults', and there are few pictures more boring than those that are technically 'perfect', but soulless. B > On 30 Dec 2013, at 16:13, Ciprian Dorin Craciun <[email protected]> > wrote: > > Hello all! > > Before describing the problem, please let me stress that I know > very well that the "quality" of a photograph lies more in its > aesthetic properties than in its technical ones. However in this > thread I don't discuss about "photographs", but "images", i.e. the raw > data (pixel values) that are totally decoupled with what they > represent. (Thus I hope I won't start a flame-war regarding > aesthetics vs. technical qualities.) > > (If you want to skip the "context" and go directly to the problem, > just go to the section titled `The questions`.) > > > == The context == > > So the problem, I always capture "images" --- note how I didn't > say "photographs" :) --- in RAW format. And, while working in fully > manual mode, very often I obtain multiple "images" of the same scene, > where the main variable is the exposure time. Also while in low > light, either interior or at night, I strive to use a low ISO like > 200-400 thus with an exposure time of about 1/10 of a second, and > although the SR is enabled, I always use continuous drive (in low > mode) to take about three exposures, in the hope that one of them is > sharper. > > The problem? During the editing process, after I select which > "scenes" are the ones I like the best, I end up with a lot of "images" > of the same scene (with almost identical composition). And thus my > problem is which of the two or three "images" is the most suitable > one, in terms of technical properties, to be used as input for > processing (thus obtaining in the end my "photograph"). > > > == The questions == > > Thus my questions are the following: > > (A) Which are the technical qualities I should look for in the image? > > (B) What software tools exist out there that would help in the > assessment of these technical qualities? > > > == My answers == > > For (A), the technical qualities, I've identified the following: > > * Is the subject properly focused? I.e. since I use auto-focus, > sometimes with slim subjects it might happen that the camera focuses > on the background. > > * Is the image sharp "enough"? I.e. not blurry due to shake, > miss-focus (back or front), subject movement, etc. > > * Is the exposure "correct" / "optimal"? I.e. especially since I > use ETTR (expose-to-the-right): > * did I overexposed something, and if so which channels, which > parts of the picture, where are the "next" shadows relative to the > highlights, etc.; > * do I have underexposed areas, and like above how much, etc. > > Did I miss other technical properties? > > I've purposely dismissed the following: > * noise -- which by its nature is a property of the sensor and > constant in effect for a given ISO value; > * depth-of-field -- which manifests itself as a lack of sharpness > for the objects outside the DOF; (although it would be nice to be > able to estimate how far a given pixel is outside the DOF;) > * flare -- they are easily discerned in the image; > * bokeh, vignetting, distortion, acutance, etc. -- which are > invariable properties of the lens (for a given aperture and focal > length); (and bokeh is a highly subjective quality;) > * chromatic aberrations -- like above, although would be nice to > highlight them; > > > Unfortunately for (B), how to asses these qualities, I have a few > theories (see the next section titled `The science-fiction`) and less > ready-to-use solutions... > > First the solutions. Currently I'm using Geeqie (an Linux-based > image manager) to find the scenes I like, and for each scene which are > the obvious failed images, i.e. those with clear over- or > under-exposure or blur, and I end up with a few candidates. However > even if I zoom 100% I don't see the raw image, but the embedded JPEG, > which was already processed by the camera, thus I can't correctly > assess the sharpness nor the exact exposure "optimality" (due to white > balance). > > Thus I then switch to RawTherapee --- which I've configured so > that by default it doesn't apply any settings at all, just neutral or > disabled values --- to look at the raw channels histogram, the exact > image without added sharpening, and the focus mask. However I can't > use the "blinkers" (i.e. underexposure / overexposure masks) to see > which parts of the image are burned, because they work after white > balance. The focus mask shows me which points are in focus, but give > no quantitative feedback of the sharpness. Moreover switching from > one image to another takes for ever. > > I know there are a few applications like Rawshack, which give me a > numerical analysis of the raw data, thus helping me assess the > optimality of the exposure. However there is no visual feedback, and > no solution for the other qualities like focus or sharpness. > > Did I miss some other tool? > > > == The science-fiction == > > However, because by trade I'm a developer, I've started pondering > about a do-it-yourself solution. My theories --- which I've started > to put into practice with a small prototype --- revolve around: > > * For assessing exposure it is clear: I take the raw image, split > it into the four channels, one for each of the 2x2 Bayer mask --- thus > without any interpolation, and at half the sensor resolution --- and > then posterize each channel with only 6 (or more) levels: two for over > / under exposure, and four (or more) levels spanning the rest of the > exposure range, approximately 2 EV apart (they can be seen similar to > the "zone" concept). I then can display these channels individually > (or recombined in a gray image) to see which levels are used (and how > much). I get thus a kind of an "exposure map", just like a heat-map > in scientific applications. > > * For assessing both the focus and sharpness: I start from the > same channels, and apply a high-pass filter, which after normalization > I multiply with the original channels (thus the result of the filter > acts like an opacity / alpha channel for the original image). Thus I > obtain an image where the in-focus parts are brighter and out-of-focus > parts are dimmer. > > * In all the operations above I apply various iterations of a > dilation filter, which helps to better visualize the areas where the > problem lies. (Although it reduces accuracy it increases visual > feedback.) > > I've been playing with a prototype that implements the above > ideas, and I can submit some samples if there are interested people. > (Currently a lot is hard-coded, and builds only on Linux.) :) > > > Does it sounds crazy? :) Does someone have some ideas I could try > out? Can one, more scientifically-inclined, point me to some papers > or similar research? > > > Happy new year! (And Sorry for the lengthy email...) > Ciprian. > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and follow > the directions. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
