HDR Image Formats

[RustBeltRaw]

I just started experimenting with HDR imaging. When I decided to try HDR, I knew the first place I'd head - the neon sign and brick wall outside Steve's Soul Food (predictable, but I've got to learn somewhere ). The colors are great at night, and there's a view straight down to Detroit's skyline.



After working on the HDR conversion, I ran into a file format problem. Didn't realize that there are dedicated formats for displaying HDR images. TIFFs and PSDs can do it, along with a few proprietary formats, but how do I get an HDR image, like my enormous 125MB TIFF, into a web-friendly format? Is it possible to produce a JPEG version with something more elegant than a screenshot of the TIFF? Converting the current image to 16-bit color, which I suspect would open the door for JPEG converion, completely borks it. Should I simply convert to JPEG before post-processing? Not sure where to turn from here. Guidance appreciated.

Incidentally, Magic Lantern turned a 7-shot AEB burst into a straightforward affair. Programmed 7 shots 1EV apart from each other, set the camera to -0.3EV, went click, and bummed around for 30 seconds or so while it took the shots automatically. Even if you don't do a 7-image composite, this strikes me as a nice, easy way to make sure you walk home with lots of dynamic range in your pocket.

[Manfred M]

Of course; you can convert the image into a jpeg.

For example:




This shot started out as three hand-held raw images that were combined into a HDRI that was output as a TIFF. I converted to a jpeg in Photoshop.

[RustBeltRaw]

I'm clearly doing something wrong, because these are the File -> Save As options in Photoshop.



I processed the files with a trial version of Nik HDR Efex Pro 2 and brought them into PS CS5 as a Smart Object. Not sure if any of that might be preventing me from saving as a JPEG...

[Mike Buckley]

Lex,

To be able to save a JPEG, you probably have to "flatten" the image file before saving it. That process eliminates all of the layers. Once you do that, the JPEG option will probably appear in the dropdown menu.

[Geoff F]

Yes, flatten or merge the layers then save as a Jpeg of a suitable size and compression.

Make sure you are using Save As etc which is creating a Jpeg copy and not altering the originals. I normally just save as a straight Jpeg with suitable settings instead of using Save for Web etc which I find needlessly complex.

Having tried several auto HDR options, I haven't been impressed with the results; so I now align the shots as layers and create a manual merge using masks which I edit as required.

[RustBeltRaw]

Tried flattening already. As you can see, the image is only one layer. Previously, it was one layer with two sub-layers from Nik.



Is this related to the fact that I'm using a Nik trial version? I would think they'd prevent any saving at all if they wanted to keep you from actually processing images with the software. And I've saved a couple other photos to JPEG while testing it. Color me stumped again.

[John Morton]

My guess is that you just haven't converted the image from 16 bit to 8 bit before trying to save it as a JPEG. The bit depth should show on the top of the open file window in Photoshop, at the right of the file name, as 16 or 8.

The screen shot of the layers palette is perfectly normal; the image is a background layer, so there are no flattening options available.

This is an HDR image produced using five exposures from a 9 exposure set. In fact, it is also a panorama composed from three image sets produced using the shift function on a Perspective Control (shift/tilt) lens; so there are actually 15 separate images brought together to produce this final photograph. I converted the RAW files to 16 bit TIFFs using Nikon Capture NX2; reduced those to 3 HDR images using FDR Tools; then used Photomerge in Photoshop to create the final compose, which I edited before converting to sRGB color space and 8 bit color depth prior to saving as a JPEG.



I'm still debating whether to redo this to get rid of the movement in the trees. Normally I would but it has been suggested to me that letting such images be as they are is also valid; and I am entertaining that perspective for a time...

[RustBeltRaw]

The issue is that switching away from 32-bit color completely changes this image's appearance. I was wondering if there was a way to make the switch without borking the color, but I suspect I'll have to convert the RAWs to 8-bit or JPEGs prior to HDR processing.

[John Morton]

The issue is that switching away from 32-bit color completely changes this image's appearance. I was wondering if there was a way to make the switch without borking the color, but I suspect I'll have to convert the RAWs to 8-bit or JPEGs prior to HDR processing.

Lex, HDR processing isn't all that different than any other kind of digital image editing. The bit depth you start with vastly exceeds the ability of any medium to portray it, including your monitor; so one vital step in the HDR process is tone mapping, which replaces the global contrasts of a 32 bit image with local contrasts that can be conveyed in a 16 bit or an 8 bit image.

There is no way to present the actual dynamic range of a 32 bit image that I am aware of; and even 16 bit images contain more information than can be printed. It is all a question of fitting your image into the space available for display, and shifting the contrast and gamma values around so that what you want people to see is available through the ways available to show it.

The conversion from 32 bit to 16 bit comes after tone mapping the HDR image; then conventional image editing can proceed before converting to an 8 bit image that can be saved as a JPEG.

[RustBeltRaw]

Thanks, John. I guess it's my tone mapping abilities that need work. But it's good to know that it should be possible to step down to 16 or 8-bit color without losing the appearance.