Dynamic range increase / DRI in PP

Hi Arcadia,

could you give me an introduction into how to work best with the "Merge with Dynamic Range Increase" function in PhotoPerfect? If possible, with some explanatory images. I haven't been too successful in using it.

Thanks a lot!!!

-Al

Hi Al,

DRI (Dynamic Range Increase) or even more well-known as HDR (High Dynamic Range) is a method to combine/merge two or more photos. The problem most digital cameras are facing is that they are only able to reproduce a dynamic range that is much smaller than what human eyes can see.

So if you are taking picture of high contrast objects, eg. a landscape with bright sky and dark ground, mostly either the sky is correctly exposed = beautiful colors and the ground is underexposed = too dark to see anything:



or the ground is correctly exposed and the sky is overexposed = too bright and washed out thus losing the mood/color you see:



No matter how hard you try, you will never get both sky and ground right, because the dynamic range in that situation exceeds the one your camera/film/chip can capture. In order to get better result, the best option is to combine the dynamic range of both photos = using the sky part of the first one and the ground part of the second.

So the requirement for DRI is getting 2 or more photos with different exposures and same framing. Either you can take many pictures using exposure bracketing and tripod to get that. Or if not possible, you can take 1 photo in RAW format and during post processing, just increase or reduce the exposure digitally and virtually creating 2 or more photos with different exposures. Depending on what camera you are using and at what ISO the photo is taken, mostly you have up to +/- 1,5 stops to play with the RAW file. More could also be possible but would reduce the quality IMO.

Now comes the fun part ;-) First please call up "Effects - Merge with Dynamic Range Increase" in PhotoPerfect and select the thumbnails of the photos you would like to combine (in the thumbnail view) and move them to the newly open DRI window. You will then see 4 sliders on the right side:

Strength:
Defines how strongly the selected brightness range overlay is implemented.

Position:
Sets the position of the brightness range to be overlaid, i.e. whether highlights, shadows or mid-range areas are to be influenced.

Width:
This parameter governs the degree of spread for the selected brightness range, i.e. how much from neighbouring ranges should be influenced as well.

Contrast:
Increases the contrast in the image in cases where transition areas appear too faint.



These are the parameters you can play with. In order to be able to use the sliders, you must first select one of the thumbnails but the first one. There is no perfect combination. You just have to play a bit to find out, what fits the photo and your taste best. In this case, I selected 241 for intensity, 108 for position, 134 for width and 16 for contrast. If you are happy with the preview, just click on "OK" to proceed to the next step: 16-bit-editing options:



Here you can find tune more in 16 bit mode. Below you can see all options available in this window (Gamma; Dimming/Brightening; Contrast; Temperature; Automatic Optimization etc...):



In this example I chose to increase the S-contrast more. After finishing, just click on "Execute" and this is the end result, which fits to my taste:



You can now see that the sky is still colorful AND the ground is also visible. Of course you can change much more but by doing this you can also risk making the whole photo too artificial/faked. I rather prefer more decent change.

Here is another result with 512;136;64;0 as parameters:



Well, in this very simple and quick&dirty example the dynamic range is only decent. The larger the dynamic range is, the more breathtaking effect/result you will be able to achieve with "Merge with Dynamic Range Increase"

Hope this helps to whet your appetite a bit ;-)

Cheers

Hoang-Tran

hi Hoang-Tran,

wow! thanks for the great explanation!
one or two more questions ...
You give the example of using two images to increase the exposure range available. does this give a better quality image than if I just - one way or another - select the lower or upper part of the image and selectively de- or increase the exposure?

Another question, you describe HDR/DRI with the intention of creating a natural-looking image. I see (e.g. on wikipedia.org) that HDR/DRI is also used in a slightly different sense, namely to create more artistical or even unreal images. I assume that these pictures were created with the same technology, just a different set of parameters, right?

thanks again!

- Al.

Hi Al,

You are welcome: -)

In principle it't the same concept. However DRI/HDR offers much better quality, because if you are merging 2 or more photos, you do not alter their exposures digitally. You only use the native exposure of these photo for merging. Whereas when de- or increase the exposure of a photo using an image editing software you automatically alter the photo itself resulting in quality degradation. The more you have to edit a photo digitally beyond its tolerance, the more you degrade its quality. So the best quality is achievable when you nail the exposure already during taking the photo.

RAW files in general have a exposure tolerance of +/- 1 stop, sometimes a bit more depending on the camera. That means that you can increase or decrease the exposure of RAW files digitally by about 1 stop without sacrifying quality = no visible degradation. Total exposure gain = 2 stops.

On contrary JPEG files have a very close tolerance. Changing the exposure digitally mostly results in immediate image quality degradation. So probabaly the tolerance here is smaller than +/- 1/3 stop. Total exposure gain < 2/3 stop

But the best is still taking multiple photos using exposure bracketing. You can either do that manually or using the corresponding function offered by most cameras. Depending on what your camera offers, you can get +/- 3 stops for JPEG files e.g. for Canon cameras or up to +/- 5 stops for Nikon cameras. If taking photos in RAW files, you will of course get even more. Total exposure gain >= 6 stops.

By using manual exposure bracketing, you can get as much exposure range as you would like to.

So you see, no way selectively decreasing or increasing the dark or light areas of 1 photo can handle great dynamic range in combination with high quality as good as DRI/HDR with multiple photos taking with exposure bracketing.

Now to your second question, which you have already answered yourself ;-) Yes, the key is lying in the combination of the parameters. By choosing the "wrong" parameters you can either create very fake looking photo as I also stated in my last post or very flat looking ones, that mean very low contrast one. So in order to get naturally and of course great DRI/HDR photos, playing with the parameters is a must.

Cheers

Hoang-Tran