A question about doing HDR from one image file

[PhotoShopNoobie]

Ok, is there any drawbacks (negatives) to doing HDR from a single RAW image?

Is there any loss of detail? An increase in noise?

[crazyfly1]

Hi photoshopnoobie,
My opinion follows;
Yes, yes, and yes.
HDR stands for High Dynamic Range. The purpose is to take two or three different exposures of the same image and blend them taking the best exposed portions of each image.
You might have seen images or training videos where a landscape is blended from two exposures, one exposed for the sky and one for the ground. Two layers are made one containing each image and the two are blended using masks to make one image that is well exposed throughout.
Same idea only done with a program (I use Photoshop cs3 Extended) that will take the best exposed pixels from the leaf of a tree or the rock that maybe got blown out with a reflection in one exposure but not the other two, (and here's the main thing) and cram all the best info from all 3 into 32 bits, a space that is soooo much bigger than 8 bit it baffles the mind.
The problem with trying to do that with one photo is that if the rock or face or sky is blown out, meaning if the RG and B channels are at or passed 255 then there is no information there...none. there is no way to make it be there. If the channels are absolute black then there is nothing there. If you have a blown out sky there simply is no magic you can do with photoshop to make it come back, all you can do is darken it and color it in.
I've seen a lot of really pretty, painterly pictures that are refered to as HDR, alot of them have incredibly saturated colors. Being able to push the colors is a bi-product of having an HDR image, a 32 bit image, being able to push up the vibrancy without making a mess of color is not necicarily the point of HDR.

Hope that helps.

[saby]

I've to agree with crazyfly real hdr is from several ldr files so U couldn't do it even from single raw(16bit), because U've not enought information for 32bit. Actually I very often use one file hdr- forgive me crazyfly- to get my image more detailed, what is like a local contrast enchantment:

one file jpg tonemapped: http://www.retouchpro.com/gallery/sh...06/ppuser/9039

and original linked here

Details can loss by increscent noise but U can control it by the tonemapper.

saby

[Robt]

I tried to shoot a couple of images to see this HDR but I wasn't impressed. Now that I see a whole section on the subject, I'll wall off a few hours and see what you will teach me.