[HDR-photo] Why does the preview look better than the finaloutput image?

[Ronald Murray]

Hello All:

If I understand correctly, to get an exact interactive preview when  
any tone mapping setting is adjusted, you would have to wait the full  
time it takes to render your full-sized file, plus wait a bit longer  
to have the fully rendered image scaled to fit the tone mapping window.

I'm not sure that the lag time it takes to do this would be  
acceptable to users. Were there any way to speed this mapping process  
up, I'm sure that the programmers would have applied these techniques  
by now. (Cell processor card add-ins, anyone?)

The only programmatic alternative would be to have Photomatix create  
a "Ring Around" option which would create a number of full size  
images while varying selected parameters systematically. In  
PhotoShop, they call this systematic preview feature a "Variation,"  
but they don't have to deal with the scaling change issue.

It would take a while to execute, but you would not have to be around  
for it. Perhaps a shortcut would be to select regions of the image  
for this treatment.

Ron Murray

On Mar 29, 2007, at 14:03 PM, Gabbygall wrote:

> Hi Geraldine,
> That's all well and good, but its still incredibly annoying, and  
> unless I
> resize quite a lot (I shoot with a 12mp sensor) then it doesn't  
> look like
> the preview at all. I like the preview. Its usually better than the  
> final
> `rendering`.  Will this be fixed?
>
> -----Original Message-----
> From: hdr-photo-bounces at hdr-photography.com
> [mailto:hdr-photo-bounces at hdr-photography.com] On Behalf Of  
> Geraldine Joffre
> Sent: 28 March 2007 11:22
> To: High Dynamic Range Photography
> Subject: Re: [HDR-photo] Why does the preview look better than the
> finaloutput image?
>
> On Tue, 27 Mar 2007 14:13:04 -0700, Bob Wise wrote
>> Thanks Geraldine... I'm not quite sure I understand.
>>
>> Are you suggesting to:
>>
>> 1) Upres the image
>> 2) Run the HDR processing
>> 3) Down-res the image?
>
> The suggestion of resizing the HDR image slightly was for the  
> special case
> when the final result is very dark and way different from the  
> preview. In
> this
> case, the suggested workaround would be as follows:
> 1) Generate the HDR image at the original resolution
> 2) Down-res the HDR image in Photoshop by a small amount
> 3) Tone map the resized HDR image
>
> The purpose of resizing in this case is to get rid of the  
> abnormally low
> values (which are confusing the Details Enhancer algorithm) thanks  
> to the
> interpolation done when resizing.
>
> For the general case of the final result looking different from the  
> preview,
> I
> was just pointing out that the algorithm is the same in both cases  
> but the
> image that is being tone mapped is different. The preview shows the  
> result
> of
> the tone mapping applied to a low-res version of the original HDR  
> image. The
> low-res version does not contain the same pixels as the original  
> version of
> the HDR image. Given that Details Enhancer takes into account local  
> details
> throughout the image, it is likely to map the low-res version of  
> the HDR
> image
> differently than its original version.
>
> The largest the difference in resolution, the more different the  
> mapping is
> likely to be. This is is why downsizing the HDR image to get closer  
> to the
> preview resolution should reduce the difference between the tone  
> mapped
> preview and the final tone mapped output.
>
> Another workaround is to use the tone mapping method Tone  
> Compressor instead
> of Details Enhancer. Tone Compressor maps each pixel independently  
> of the
> local context, making the preview a reliable representation of the  
> final
> result.
>
> Geraldine Joffre
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