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05-12-2009, 04:52 PM   #16
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QuoteOriginally posted by bymy141 Quote
HDR is a method and an image storage format (like JPG and RAW are).
??? Hadn't heard of a specific HDR file format before. Who uses it?

QuoteOriginally posted by bymy141 Quote
In order to be able to contain that dynamic range, the HDR format stores pixels in floating point format instead of integers. Enabling infinite dynamic depth.
If the original RAW data is integer based, how does converting it to floating point gain you anything? In other words, isn't the dynamic range limited by the precision of the original data?

05-12-2009, 05:37 PM   #17
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QuoteOriginally posted by bymy141 Quote
Creating HDR pictures from ONE (1) RAW file is not possible
See, I hear conflicting reports on this. I've read tutorials the last few days, and seen some amazing HDR photos, that were generated from 1 RAW file. I do understand that the *best* way is to shoot multiple photos at multiple exposures in your camera, and then combine these to create the HDR effect. I got that. I understand it.

But as I've said, this is not really possible when trying to capture multiple images of my son who is running from third base to home. No matter how fast the burst is on my K20D, he's going to run many yards between the first shutter click and the last.

This is where pseudo HDR come is... the process of shooting one RAW file, then using software to bracket it up 2 stops and down 2 stops, and then creating an HDR image from these three files.

As I stated a couple times already, I know how to, and have successfully done wonderful *true* HDR photos using the auto-bracketing feature on my K10D. But they are only landscape photos and not action photos.

What I am trying to learn is how to do pseudo HDR.

I've been given some great tips here and I'm excited to try them.
05-12-2009, 06:55 PM   #18
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A lot of the issue is about processing method. Many of the HDR tools work by taking several exposures and combining them into a single image with a greater dynamic range, which they then tonemap into the desired form.

When starting with a single RAW image, artificially bracketing it with software cannot add any dynamic range that wasn't already there to start with; it's just manipulating the output levels, which is not much different from what HDR software would do during tonemapping. Therefore you shouldn't need to software bracket -- the HDR software should be fully capable of taking the single RAW image with its existing dynamic range and tonemapping it into the desired result.

I don't know how Photoshop does its HDR work, but that probably explains why you don't get good results with software-adjusted exposure.

Where artificial bracketing can work is with software that does exposure blending, such as enfuse. All I have sitting around at the moment is a scratch image that wasn't exactly exposure-adjusted, but should help illustrate the technique:


One of the experiments done with that same RAW image was producing a version with a steep gamma curve (for the clouds), which was then blended back using enfuse. Other processing tweaked contrast and similar, but the result was:


You can get better (more natural) results with simple exposure adjustment, but I don't have any examples handy.

Supposedly you can also do this sort of thing using only Photoshop and the original RAW image, without anything resembling HDR or exposure bracketing, but I'm not familiar with Photoshop to know how. I find the exposure blending technique to be straightforward and yield good results.

Last edited by Quension; 06-22-2012 at 07:08 PM. Reason: change in image hosting
05-12-2009, 07:42 PM   #19
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QuoteOriginally posted by Gooshin Quote
you cannot do HDR from a single RAW file because when you load up all the derivatives into photoshop, it still recognizes them as all being "the same image" so it gives you the finger.

i have been informed however that if you completely strip the EXIF info from the output image, then you can proceed with creating an HDR from a single RAW file.


for proper HDR, you have to take multiple PICTURES at different exposures, and put them together, this is where a tripod and mirror lock up come in + in-camera bracketing.


but if you just want to work off a single file, just start exporting bracketed jpegs with their exifs stripped then put them all together, the result will be less than perfect, especially if you have blown highlights or complete blacks, but can get some results non the less.
This is not quite true. If you create virtual copies of the image you can add and subtract exposure on each of the copies independently. I use Photomatix, and one of my students had taken a very difficult image of a couple in the doors of a stable with full sunlight outside. The sunlit building and fence were over, the stable had no visible detail. This particular file was NEF from her D80. It works the same with PEF.
  1. Created a virtual copy and subtracted one stop of exposure
  2. Created a virtual copy and added one stop of exposure
  3. Exported both as full size jpegs
  4. Opened Photomatix
  5. Selected the two images
  6. Assembled the final image by using Photoatix Highlight and Shadow two image combination.
If anyone wants to see this, I can ask the student for permission to display.

05-12-2009, 09:15 PM   #20
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I'd love to see the result, and the original image.
05-12-2009, 10:18 PM   #21
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HDR Images

The original image was taken with a Nikon D80 and VR 18-200mm lens by a student. In order to demonstrate the use of Lightroom 2.2 and Photomatix to create an image that showed all detail without being cartoonish, I created two virtual copies of the image. I then took one of the copies and reduced exposure one stop, and increased exposure one stop on the other copy.

I tried Photomatix HDR with all three images, but it did not look right, so I tried only the exposure adjusted copies and Photomatix Highlight/Shadows function. It worked quite well, I think

Here is the original image, resized for the Gallery, of course, exported as JPEG. Note how the scene behind the couple is overexposed, and the stable is all but invisible.



The first copy corrected the outside, but the stable has gone black.



I created a second virtual copy and increased the exposure by one stop to show some detail in the stable, completely blowing out the scene outside the doors.



The final image combined the one stop over and one stop under exposed images using Photomatix Highlight and Shadow option.

05-13-2009, 01:42 AM   #22
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QuoteOriginally posted by ccrookston Quote
And Ben, what are the advantages of saving as a 16 bit .tiff over a high res .jpg?
A 16-Bit Tiff can store the complete colour depth of the original RAW file - and leaves some headroom for processsing (as many RAWs, including PEFs only use 15 or 14 bit), whereas a JPG always only has 8 Bits colour depth, which translates into only 1/256 of the colours a Tif file can represent (Jpeg > 3 x 256 colours versus Tiff 3 x 65536 colours).

So for processing a 16-bit image will guarantee, that you do not loose colours and don't get posterization. For final output in print or on screen a conventional 8-bit image is fine, though.

Ben

05-13-2009, 05:45 AM   #23
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were the exif's stripped?

QuoteOriginally posted by Canada_Rockies Quote
This is not quite true. If you create virtual copies of the image you can add and subtract exposure on each of the copies independently. I use Photomatix, and one of my students had taken a very difficult image of a couple in the doors of a stable with full sunlight outside. The sunlit building and fence were over, the stable had no visible detail. This particular file was NEF from her D80. It works the same with PEF.
  1. Created a virtual copy and subtracted one stop of exposure
  2. Created a virtual copy and added one stop of exposure
  3. Exported both as full size jpegs
  4. Opened Photomatix
  5. Selected the two images
  6. Assembled the final image by using Photoatix Highlight and Shadow two image combination.
If anyone wants to see this, I can ask the student for permission to display.
05-13-2009, 08:24 AM   #24
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QuoteOriginally posted by Gooshin Quote
were the exif's stripped?
Yes. The EXIF data is of no value for the purpose of the image presentation.
05-13-2009, 08:32 AM   #25
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QuoteOriginally posted by Canada_Rockies Quote
Yes. The EXIF data is of no value for the purpose of the image presentation.
so then there is nothing incorrect about what i said.
05-13-2009, 08:36 AM   #26
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QuoteOriginally posted by Gooshin Quote
so then there is nothing incorrect about what i said.
No, I was not implying there was. I apologize - my response sounds a bit snippy.

[Edit] I just reread your earlier posts, and see where my post might be taken as a contradiction of your posts. It was not meant to be. It was meant as a method of getting better results from a single image by tricking the HDR software into thinking that more than one exposure had been used when the dynamic range was too great, but within a stop of exposure at both ends.

Last edited by Canada_Rockies; 05-13-2009 at 08:44 AM. Reason: Clarification of trickery in fake HDR example.
05-13-2009, 09:25 AM   #27
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Also, it should be noted that this particular method of "faking" HDR isn't the only way. Similar results can be obtained more directly one a single copy of the file using controls such as curves, local contrast enhancement, highlight recovery, fill light, shadow/highlight enhancement, etc. Different applications implement these controls in different ways and with different names, so I'm not sure exactly how that might be done in Photoshop, but you can get pretty much the same results in ACDSee using the "Light EQ" tool.
05-13-2009, 10:12 AM   #28
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QuoteOriginally posted by OregonJim Quote
??? Hadn't heard of a specific HDR file format before. Who uses it?

If the original RAW data is integer based, how does converting it to floating point gain you anything? In other words, isn't the dynamic range limited by the precision of the original data?
It is not the precision, but the absolute range that you can handle per pixel that is important in HDR.
See: Radiance HDR (.pic, .hdr) file format
Of which I quote: "one byte mantissa for each r,g,b and a shared one byte exponent".

The file format is not limited by the 8 or 16 bits ranges of JPEG and TIFF.

Of course the absolute range is limited by the original data, you are right there.
That's why you need multiple pictures with overlapping data ranges in order to increase the total dynamic range of the compiled resulting picture.
And that is why you cannot create an HDR photo from 1 shot!

Suppose one RAW picture contains 12 stops dynamic range.
Suppose you take 5 bracketed pictures in a row that start with -4 all the way to +4 stops, you can create an HDR picture of 12 + 4 + 4 = 20 stops.

- Bert
05-13-2009, 10:58 AM   #29
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A somewhat long reply, explaining a bit more about HDR

I feel I need to do some more explaining on HDR.
There are 2 big problems with HDR:

1. Capturing the extended dynamic range by multiple photos with overlapping exposures to create one photo with more dynamic range than a common camera can capture.
2. Displaying the HDR results using our common and available LDR display devices.

The first problem is attacked by many software packages, and when properly stored will generate an HDR picture in HDR format for you. This, by the way, is an art in itself.

The last problem is not often explained and commented.
Not only our capture device (camera) has a limited DR, output devices like displays and printers have the same if not worse limit! So, now you have your HDR picture in the file, how are you going to display the extended range? If you have a DR of 30 stops and your display or JPEG file can only handle 20 stops, how can you ever enjoy the results?

The trick is to intelligent compressing the dynamic range again, where dark passages are highlighted and light passages are darkened. Unfortunately, the effect between dark and light passages of the picture is smoothly transitioned from dark to light, creating the typical HDR look and feel. Most of the time this results in removing DR out of the middle passages.

Of course you may want to compress the DR differently, have more visibility of dark or light passages, however, you might as well just have a look at one of the original pictures you took.

One can simulate HDR look and feel effects, for instance with Lightroom, see: Using Lightroom to simulate HDR effects
But, these results are NOT true HDR pictures.

In a few pictures, you could see the results as follows:

Attachment 34515
Attachment 34516

Combining multiple pictures:

Attachment 34517

A photo with the typical "HDR" look, looks like this:

Attachment 34519

Now, look at the sky, around the trees you can see the strong halo effect.
This is caused by highlighting the trees that are dark and darkening the sky that is light. This result is typical for Photomatix.
It is easy but "not so very good" in my opinion.
This effect you can of course get with one picture as well, however, as stated before, it does not make it a HDR picture.

I hope this somewhat long post helps you understand.
Have fun!

- Bert

Last edited by bymy141; 06-18-2009 at 08:25 AM.
05-13-2009, 11:21 AM   #30
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QuoteOriginally posted by bymy141 Quote
I feel I need to do some more explaining on HDR.
There are 2 big problems with HDR:

1. Capturing the extended dynamic range by multiple photos with overlapping exposures to create one photo with more dynamic range than a common camera can capture.
2. Displaying the HDR results using our common and available LDR display devices.
Right, and it's the latter issue that causes many attempts to look "fake" to many people. If something *really is* 8 stops brighter than something else, representing it as if it were only a couple of stops different is not quite right. There ways of doing this can be more convincing than others, but at some level, you are definitely telling a lie in some sense.

On the other hand, if one had a true HDR device to display the image on, results could be breathtaking.

Of course, traditional photography is a lie of a different sort - one that says it is impossible to see details in both highlights and shadow. But it's a lie we've become accustomed to - one in fact that that artists have presented to us for centuries, because it's the same lie told by most "good" representational art.

All these are caused by the fundamental problem that traditional displays - canvas, prints, computer monitors, etc - limited you to a relatively small number stops of range from the lightest lights to darkest darks, and that's just not how the real world is.

QuoteQuote:
One can simulate HDR look and feel effects, for instance with Lightroom, see: Using Lightroom to simulate HDR effects
But, these results are NOT true HDR pictures.
Right - I'd say they are capturing one of the *effects* of an HDR photo (visible detail in both highlights and shadow) but not actually givign you more dynamic range in the literal sense.

BTW, those pictures you posted illustrating the different ways of compressing dynamic range - they look almost *exactly* like the pictures Doug Dawson (a well-known painter and teacher) uses in explaining similar concepts as they relate to painting. The idea being that the real world a large number of discernible steps of value from lightest lightest to darkest dark, but a painting can capture only a more limited number. He draws a similar long rectangle to represent the real world, a shorter rectangle to represent your painting, and draws a series of lines form one to the other shows the various ways of mapping the real world to the painting. The one where you simply compress everything to fit is presented as the "wrong" way, as it tends to miss the quality of light that representational painters are usually so interested in capturing.
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