I found it on line. It appears to do what HDRs are supposed to do with lighting.
Is there no way to begin with a JPG and turn it into such an HDR?
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In theory, you can bump the contrast to what is expected for an outdoor HDR (in Photoshop), and then use a blur tool to smooth out the stepping that results. That might result in detail loss though (and might be work intensive) so your mileage may vary
a 32 bit floating point image can have " 3.402823 × 10^38 " pixel values
basically any realistic positive and negative value
as above you really can not convert a 8 bit rgb jpg into a 32 bit rgb image
it will still have the 8 bit pixel values
red = 255 tones
green = 255 tones
blue = 255 tones
now there is some rendering “magic” that can use additional 8 bit images as a multiplier and make them behave like a
16 bit unsigned image ( values from 0 to +65535)
or a 32 bit INTEGER image ( [ 2^31 - 1 ] tones )
Is there no way to begin with a JPG and turn it into such an HDR?
not really
However there are ways to inpaint with synthetically created missing information
as above a blure ??? might - but not well
i normally use a PDE heatflow
Using the image as input into calculating the the energy flow of temperature in a system over time
G’Mic uses this
but results will vary, some will look good other images will look like SHIT
OK, I understand. I am producing my own equirectangulars, but am limited to JPG. I’m getting beautiful skys, but no bracketing and no RAW format. So I think I better live with the results and use a sun.
Thanks very much for all the information.
JohnW, one more question: is the rendering “magic” something I do using Compositing nodes?
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Although I have some difficulty to follow some explanations on the posts above, I think there still some misunderstanding about hdr images and their use.
What makes them good at reproducing natural lighting in 3d is not the fact of having a high range in itself, but how this fact is used to generate a great difference from lights and shadows in the image, that is only achieved through the adding of several shots of the same scene at different expositions into one single hdr image.
When you simply convert an 8 bit image into a 32 bit what you get has the same range of the original, you not even get softer transitions unless you blur the image afterward; this does not change the fact that when you use it for lighting a 3d scene you have to rise its brightness a lot to reach the power of the sunlight, but this way also the lower lights and dark parts are raised as well, reducing the contrast dramatically.
A good hdri for lighting must have at starting a great difference between sunlight and shadows, and the only thing you can do is to increase the brightness of the sun disc in photoshop; slight tweaking of exposition and gamma barely can manage it.
paolo
SUMMARIZING:
I can convert a 32 bit HDR file (of sky with sun) to an 8 bit JPG and - to my eye - they appear identical, but in Blender the HDR produces realistic sun shadows, but the JPG does not.
Obviously then, there is an invisible difference. No one - including me - may know how to start with the JPG and turn it into an HDR that has the invisible magic in it, but I can’t help thinking that it must be possible. The invisible values must have a proportional relationship to the visible values that could be calculated and used to modify the file - a kind of stretching of whites to whiter and blacks to blacker, with middle tones not changing.
This 32bit invisible magic is a separate issue from the high dynamic range issue. I understand bracketed exposures but do not need them for skies since I am unconcerned with the (usually darker) ground; skies are all bright. What I need is the invisible stretching that allows Blender to see the sun as much brighter than the surrounding clouds.
I wish I was smarter, but I was educated by the government.
[QUOTE=Obviously then, there is an invisible difference. No one - including me - may know how to start with the JPG and turn it into an HDR that has the invisible magic in it, but I can’t help thinking that it must be possible. The invisible values must have a proportional relationship to the visible values that could be calculated and used to modify the file - a kind of stretching of whites to whiter and blacks to blacker, with middle tones not changing.
[/QUOTE]
I’m just a beginner here, but let me try.
The difference is invisible, because the image you are looking at is limited by the dynamic range of your monitor screen. You cannot see true hdr on your screen, just an interpretation of it.
No, I tried to explain the matter just a post above, and probably the cause of your perplexity is what stilton has well pointed out; an 8 bit image cannot contain a range of values grater than 255, there’s no room for the huge differences of luminosity of the reality, so no magic is possible.
I’ve got to tell you, sourvinos, Your explanation is kinda technical, it overpowers what I felt was a simple concept with too much detail.
I can understand John Howard’s confusion, he’s debating image bits and values with you, when the conversation should be about referred and display color space. … I think I’ve got that right!
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If in the 8bit photo you have two neighboring pixels showing as white when one of them represent the cloud at white and the other one represent the sun at a gazillion, there is no mathematical tricks you can do to get them to be different. Any mathematical correction you do to one of them will also affect the other given the input is identical.
Sure, you can boost luminosities 250-256 to become 25000-25600 with ease, the problem is it’s the values above say 1000 you want to scale, and with an 8bit image you don’t have that info.
Many of the replies to my last post seem to assume that I wish to end with an 8bit JPG image. I was contemplating a 32bit image made FROM the 8bit JPG and THEN (after some magic stretching of the whites and blacks) saved as a 32 bit HDR or EXR, which - to the eye - would appear the same as the original JPG. I apologize if I was unclear.
I have been able (since last writing) to turn a JPG into a 32 bit HDR and have the sun cast shadows by selecting a circular area at the sun and then increasing the exposure value of that area only. The change is invisible to my eye, but it works. It’s not a perfect answer because I am only adjusting that one area.
Removed due to donkey.
The “cheat” is working. Perhaps you should pay attention.
Removed due to donkey.
It really isn’t working. Scaling just the sun part of the image is no different from using just the image and a sun lamp, which lands you right back at the start of the thread.
Please reconsider based on the very useful information being posted.
Some of you little scolds really need to learn that it is always a mistake to treat strangers the way your stupid parents treated you.
If I am able to “cheat” a sun into a false HDR based on a JPG, then from then on, I can switch skies in a scene without having to reset the sun. That does not land me back at the start of this thread. You scolds tire me out.
I wish to thank all those who have offered so much valuable info. It will take some time to absorb. Have a good New Year.
As someone that took the time to try and provide insight into your original question, this pisses me off being labeled a “little scold”.
If you don’t want information, don’t fucking ask.
There isn’t a single person in this thread that has responded to you that should be labeled with such condescension.