I don't find "Exposure levels" there.
June 16, 2023
577
-
-
Word for word, interesting, thanks.
-
keep reading
-
I like the wording.
Identical exposure settings shutter+apeture+iso
-
what does these histogram tell you about the exposure
Notice how the patches show differently in the 2 histogram even when they represent the same lab values.
How those values are shown in a histogram vary depending on what that distribution of data represents in a color space.
(both are of jpg images and not raw) -
So what? I don't see the point you are trying to make.
When using flash you have 2 exposures* to deal with - the ambient exposure* and the flash exposure*
The flash exposure* can be set automatically by the camera using ETTL or manually.
Even though the aperture, shutter speed and ISO are the same in both shots the total exposure* for Screenshot(5) was larger because more light from the scene hit the sensor due to the additional light added to the scene by the flash.
The 2 luminosity histograms are about what I would have expected for those shots.
* exposure - amount of light that struck the sensor per unit area while the shutter was open
-
Both articles are misleading. Capturetheatlas more because he determines the exposure using LR histogram, not the RAW one.
Artschoolportals article is better but I don't like the way they use PS Levels as example of exposure. -
They are not here is a hint for part of the scene you introduced more light thus altering the exposure
-
The exif for the shots shows the aperture, shutter speed and ISO are identical for both shots but the exposure* is not the same as described earlier.
* exposure - amount of light that struck the sensor per unit area while the shutter was open
-
You are misunderstanding what is explained in those articles.
Consider this image with pure red (255,0,0), green (0,255,0) and blue (0,0,255) pixels on a pure white (255,255,255) background.
This is the RGB histogram for the image.
This is the luminosity histogram for the same image.
A histogram of any kind - RGB, Luminosity, whatever - is just a frequency count of some values - RGB, luminosity, the number of various coloured cars crossing an intersection etc etc etc - and nothing more.
-
im not disputing that. have you a better way to show scene luminance ?
-
Im not disputing that. so explain the relevance/measure of scene luminance without the histogram.
-
Scene luminance is basically the light coming from the scene and I gave examples of both the RGB and luminosity histograms for a given image earlier.
I explained what the histograms are and represent in the earlier post and in the post I linked to.
-
your not answering my question. i will put it even more simply what advantage is knowing scene luminosity measure .(even though no one can even put a value on it) compared to just using the EVF considering it shows the most detail from any form of measure . so WYSIWYG is basically the ultimate luminosity meter.
-
The histogram in the EVF is based on the rgb values in the image data generated from the raw data.
It isn't a histogram of the raw data generated by the light hitting the sensor.
-
the raw histogram can not show fill flash levels 😁 in fact its useless in the field compared to the EVF
-
When you design a sensing system you start with a transducer, the device that turns whatever you're sensing into something you can measure - usually electrical voltage. Quite often what you want to measure is not the thing that you're sensing directly but something that you can derive from something you can measure more easily. For instance, ammeters usually work by measuring the voltage across a resistor, not the current(amps) directly. Then you'll generally have some signal processing - which conditions the signal (where 'signal' means the 'message' that you're trying to receive), does any processing that is necessary to extract any derived measurement from the data that you actually have , and converts it into a form that you want to display or log. Whilst the data from a histogram (and indeed the final image) is derived from the scene luminance, it's not directly measuring the scene luminance. A number of processing operations have been done which convert it into a different form, which is essentially a recipe for rendering a scene. Think of that as like painting by numbers - a list of paint colours and a drawing of the scene with a number in each patch saying which colour should go there. When yo've painted the scene you know something about the distribution of luminosity across the scene, but from the painting by itself, you couldn't make a good estimate of what the original scene luminance was.
-
Thanks Bob, i like to call the resistor a shunt resistor 😊
in fact when im setting up amp meters in yachts i actually use the negative 400 amp battery cable and spike a wire in and use a 10millamp meter to read the amps.
