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HDR,What is it?
I may have missed something along the way here. I keep coming across the expression HDR pictures in the other forums; everybody seems to understand what it is but I'm afraid I can't work it out. Am I missing out on something? Help!! Help!! John..

Comments (11)

Hate to sound like a smart alec, but I'd try Google first. Its quicker...

Comment #1

HDR = high dynamic range, which can refer to a number of things..

- The dynamic range of the scene- The dynamic range of the image file- A high dynamic range compressed into a smaller dynamic range file- Editing and blending a sky exposure with a foreground exposure.- etc, etc, etc.

Http://en.wikipedia.org/wiki/High_dynamic_range_imaging..

Comment #2

A loosely-defined range of techniques to capture or express images that exceed the usual ~5 stop dynamic range of today's photosensors. This often involves combining image data that is "overexposed" and "underexposed," and toying manually or mathematically with the mixture..

[ e d @ h a l l e yc c ] http://www.halley.cc/pix/..

Comment #3

Actually, that term is more often than not used in the wrong way. As others have pointed out, HDR stands for 'High Dynamic Range' and is simply a 32 bits format that allows for a dynamic range that is even bigger than a 16 bits format could hold. However, you will often find people referring to the 'HDR effect'. In that case, they are referring to the fact that many people use HDR images to create strange (and in my view ugly) effects. Those effects have nothing to do with HDR as such though, you can also create them by using non-HDR images. The effect is created with a technique called 'tone mapping', which is a technique normally used to compress the tonal range of HDR images.

By using tone mapping in another way than intended, you get this so-called and ugly 'HDR effect' people are talking about..

Johanhttp://www.johanfoto.com..

Comment #4

To do hdr-.

If you put camera into full auto matrix metering, take first shot note fstop and shutter speed. put camera into full manual, see if camera still has the matrix fstop and shutter speed. if yes, then using shutter speed go up 2-4 shutter speeds 1 fstop worth of shutter speed at a time. the back to matrix shutter speed and go down same number of shutter speeds.this is on a tripod with cable release..

No, you should not use 1 raw shot and convert 1 stop up and down, because their is not enough dynamic range in the 1 raw shot. dynamic range is why we are doing this, hdr is trying to get all it can..

The group of shots can be raw or jpeg. if jpeg they can be used as is. if raw remember that you HAVE to batch process all 5-9 shots. this is because the pp has to be all the same on every pic. you cannot, for example make any attempt to get the shadow details of the group of raw pics, because that would require different amounts of pp, and you cannot do that with hdr. the pp for all shots has to be identical..

For me I just shoot them in jpeg and use them from the camera, that way they are all identical because the camera jpeg settings are the same for every shot. I also put my hand streched in front of the lens and take a check shot and when done take a ending shot with hand. this tells me where the hdr group is on my memory card when I transfer to the pc..

The only important item is to bracket using shutter speeds only. if fstops are used it changes dof between shots. and shoot enough shots, 5-9 is the optimum. the only other thought is to shoot a scene that deserves the the hdr technique, too many people are shooting hdr because it is new or different or whatever. many people are using hdr software on scenes that do not have enough dynamic range; they end up with images that have been enhanced by hdr software, they are not hdr images. the dynamic range was not in the scene to begin with.

This can be checked with a spotmeter on different areas. NOTE: use of auto bracketing on a camera may not work unless you know the bracketing is using the shutter speeds to bracket. in any event, you really need 5-9 shots for hdr; this is more than the auto bracket fcn on almost all cameras. and the bracketing has to be both sides of the middle shot. make you use enough brackets to cover the previously checked dynamic range.

And the scene should have no movement, if so the item will blur in the hdr image..

Do not adjust the focus. set the focus on infinity or use a hyperfocalsetup for focus..

Do not adjust the white balance for individual shots. go with awb or 1 setting and do not change it..

Remember, hdr was created and meant for scene that have a dynamic range that exceeds the dynamic range of the camera sensor, about 5-6stops. hdr with the required software allows the user to capture a scen that has very high dynamic range...

Comment #5

The 'high' in 'high dynamic range' is subjective, and does not refer to any particular file format or bit depth..

A raw file is an HDR image compared to a JPEG file...

Comment #6

True, but that is semantics. The term 'HDR' is normally used for 32 bit images. It's the same as saying "What is large? Compared to a 4x 6 inch print a 8 x 12 inch print is large". That may be true, but when people are talking about a 'large format printer' they don't mean an A4 or even an A3 printer..

Johanhttp://www.johanfoto.com..

Comment #7

GaryDeM wrote:.

Remember, hdr was created and meant for scene that have a dynamicrange that exceeds the dynamic range of the camera sensor, about5-6stops..

5-6 stops fits easily in the range of a sensor. You mean 5-6 exposures, which *adds* 4-5 stops over the range of the sensor..

Johanhttp://www.johanfoto.com..

Comment #8

No I meant 5-6 stops, which is the same as slide film. read this article, the author talks about the number of stops in a sensor faily early in the piece..

Http://www.luminous-landscape.com/tutorials/hdr.shtml..

Comment #9

I think you misunderstand him, because he is actually confirming what I say:.

The author says: "For the sake of this discussion, let's assume that a typical colour transparency film or digital camera sensor can record 6 stops of dynamic range". That's what I'm saying too. A normal sensor can record those 5-6 stops you are talking about. You don't need HDR for that..

The author also says: "As we'll see in a moment with a practical example, this has the potential to allow photographers to create a photograph with 10, 12, or even more stops of dynamic range. " That's what HDR is all about, not 5-6 stops..

A bit further he says: "Not every image needs to have 10-15 stops of dynamic range. In fact, most photographs look quite nice, thank you very much, with the 5-7 stops of dynamic range that we're used to." That means that he again confirms what I'm saying, namely that a normal non-HDR image is 5-7 stops..

Johanhttp://www.johanfoto.com..

Comment #10

We are saying the same thing after all. I thought you meant to say that HDR is 5-6 stops, but you mean that the sensor is 5-6 stops, so HDR is *MORE* than that. We agree after all..

Johanhttp://www.johanfoto.com..

Comment #11

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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