What is LDRI?
Before you know what is a HDRi, I will say that is a LDRI. It’s nothing more than any image we can see on the internet or photos that we have done with a conventional camera and is called Low Dimanic Range image (LDRI or just LDR: low dynamic range) that contains minimal information of light and shadow it is necessary to represent our photo.
A LDRI file is used in websites, slideshows, TV, print, etc., it can be .jgp, .png, .tiff, .bmp, .gif, format, etc..
I will show you an example with the following image:
I have taken a picture and see how the object is closer clearly shows, however what is behind this too bright without coming to appreciate what is good.
I will try to fix this in the next picture:
Now with the same camera I made another picture trying to make the background look good, as in the previous photo was brightly lit, as shown, what is behind the window looks good but our object is closer this very dark.
That area of the first image that is too bright in photographic terms is said to Overexposed, the area of the second photo that is too dark is that it is Underexposed, photos of both the place that looks good is said to properly Exposed
These two photos above lack of light information to look good, the first picture is missing information shadows, the second photo lacks lighting information, so images are low-level information (low dynamic range).
But …. and if we take the two photos only part that looks good and put them together? that’s where HDRi comes in.
So what is Hdri?
As I showed above what is LDRI, the High Dynamic Range image (HDRi) is the opposite, that means it is an image that contai1ns information stored both lights and shadows which is able to capture with a camera photos.
This range is captured with a camera shown in «Steps» and is represented by the acronym EV.
A HDR or HDRi file is the same and usually carries a .hdr or .exr some may be also .raw, .tiff and others.
At present the HDR as such can not be displayed by any monitor, TV screen, or any device that projects images since even these lack the technology to display all the information of a hdr.
Knowing a little about photography
I’ll explain a bit more about photography oriented for HDR imaging. If you’ve ever had a professional or semi-professional camera in your hands you will have seen that there is a photo to the automatic option and the manual option. With the automatic option the camera chooses his values apparently lighting should have our picture and make photo, but this option is not worth to make a HDR. The best way is to take the HDR with the manual option, because with that you can control the EV steps ie can take a series of consecutive shots to capture lighting and shadows.
In photography there is the exposure time (shutter speed) which is nothing but having the control to overexpose, expose correctly or underexpose an image.
If you look behind the viewfinder of a professional camera or semi-professional camera you’ll see something like this:
Camera viewfinder
Among many things, seen in the bottom left a number which in this case is 200 (1/200), this value indicates the exposure time will take your photo, this value you can manually increase or decrease to overexpose or underexpose as you see fit.
Below you’ll see a chart that normally have exposure cameras:
Table shutter speed
This table can vary from one camera to another, but in general each value is an exposure time and jump from one value to another contiguous counts as «step» or 1 EV (1/60 to 1/125 is a step or 1 EV and 2 to 4 is a step or 1 EV, etc etc) so we have 1/15 to 8 are 8 EV’s. We can say that there are intermediate values between one step and another, as shown in the photo above the 200 would be a middle of the 125 and 250. Therefore to create a HDRi you need to do a sequence of several shots with different exposure times and then join them into one and get a high dynamic range.
In the tutorial parameters and camera settings I explain more about shutter speed, aperture, distance, focal length, ISO, depth of field, and many tips.
How many Ev’s need to create a Hdri?
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good tutorial and very good explained