RAW, HDR and related resources
Since my post about RAW there's been a lot of interest and a number of questions have been thrown up. So this post gives links to and discusses resources that answer them and that I've found useful.
In the full article from The Luminous Landscape, you'll read that most of the available levels of brightness that come out of a sensor's cell get allocated to the right hand side of the histogram, only a few to the left and a middling amount to the middle.
It's essential that you get this point because when you do you'll realise that the right hand side of the histogram is where you get most sensitivity to differences in shades and the left hand side the least.
Note that for HDR this means that you'll need more exposures for the shadows than the highlights to get the same number of shades (tones) in each.
The Luminous Landscape have also got a useful link to an article on understanding histograms.
I only convert to 8 bits at the end of my workflow, when moving to jpeg:
Before you download it, consider some things first. The company and software was bought by Adobe in 2006 and incorporated in Adobe Lightroom and Photoshop (see a tutorial on using their Camera RAW plug-in). Rawshooter doesn't support a lot of cameras released since the buyout, including Canon’s 5D, 40D, 450D/Digital Rebel XSi, and 400D/Digital Rebel XTi; and Nikon’s D40, D40x, D60, D80, D3, and D300. Download it here.
The image used is one from my Urban Decay, Lost Spaces and Industrial Ugliness photo essay.
That's all for this post. As usual comments, additional info, opposing views(!) are all welcome :)
Stumble It!
Expose so you bias the histogram to the right
...but without blowing the highlights.In the full article from The Luminous Landscape, you'll read that most of the available levels of brightness that come out of a sensor's cell get allocated to the right hand side of the histogram, only a few to the left and a middling amount to the middle.
It's essential that you get this point because when you do you'll realise that the right hand side of the histogram is where you get most sensitivity to differences in shades and the left hand side the least.
Note that for HDR this means that you'll need more exposures for the shadows than the highlights to get the same number of shades (tones) in each.
The Luminous Landscape have also got a useful link to an article on understanding histograms.
Work in 16 bits for as long as possible
The topic of bit depth is covered in a quite digestible way here.I only convert to 8 bits at the end of my workflow, when moving to jpeg:
- I save my final file while it's still 16 bits so I can go back to it later, when needed
- Then I convert to 8bit, do some final touch-ups such as noise removal and sharpening suited for the uses I'll put the jpeg to,
- Then it's a save as, using jpeg as the file type.
Downloads and other links
Rawshooter Essentials
I still use Rawshooter for working with RAW, whether for preparing multiple exposures for my HDR workflow or the single 16bit TIFF ready for the Photoshop part of my workflow. It supports my Canon 350D's RAW files. If you do use it, it's vitalBefore you download it, consider some things first. The company and software was bought by Adobe in 2006 and incorporated in Adobe Lightroom and Photoshop (see a tutorial on using their Camera RAW plug-in). Rawshooter doesn't support a lot of cameras released since the buyout, including Canon’s 5D, 40D, 450D/Digital Rebel XSi, and 400D/Digital Rebel XTi; and Nikon’s D40, D40x, D60, D80, D3, and D300. Download it here.
Noise Ninja
I use Picturecode's Noise Ninja to correct the noise I get in HDR work when I wasn't able / didn't(!) follow the advice in the article above... There's a free version but it only works on 8bit images, so useful only as a final step when converting to jpeg. Download hereDynamicPhoto HDR
I haven't tried Photomatix, though many swear by it. My own preference is DPHDR. Download here. The page gives a great explanation of where HDR is useful and what it does.Video tutorial
I've put together a tutorial showing the processing from RAW to finished HDR image. It's twenty minutes long but don't let that put you off -- lots of people have said how they found it easy to follow and understand :) See it here.The image used is one from my Urban Decay, Lost Spaces and Industrial Ugliness photo essay.
RAW explained in more detail
For those who want a more detailed explanation of how RAW works (rather than what it does for you, as I covered) read this.That's all for this post. As usual comments, additional info, opposing views(!) are all welcome :)
Labels: HDR, links, RAW, resources, tutorials
Stumble It!
posted by Highton-Ridley at
10:45
3 Comments:
Mark,
Thanks for all the help. I am having an HDR weekend! I am becoming addicted to it. Only tried a few so far and working out the settings etc to get used to Dynamic HDR. I downloaded the Trial version of Photomatrix pro to try as well.
I am (as most probably do) having a bit of frustration with alignement of the three images. I am using a tripod, Aperature priority and multiple shot mode to minimize movement but still getting some...I think it is windblown leaves as the exposures are made. Anyway...thanks to you, I have a whole new owrld to explore.
Dan
The trouble, as I see it, with HDr is it gets a bad reputation from too many cartoon images with a severe halo effect. I use Photomatix, but feel the images are much too soft for my liking.
both you and Mononeil say to expose to the right. But I have been reading about exposure from many sources about the tone zone and 18% gray, etc.. Look for tones and compensate the exposure for that tone. In other words, mid tone blacks would be compensated at a -1 exposure. But this would stack the histogram to the left.
OK, that was a lot of typing. My question is, how do you expose to the right if you are shooting for particular tones?
Anyway, thank you for stopping by my photo-blog, it's a continual work in progress. I look forward to learning more while surfing through your sites.
@Dusty: Yes, you're right about the saccharin eye-candy effect a lot of people go after with colour HDR.
I prefer Dynamic Photo HDR for my mono work and I find that the default ultra-contrast tone-mapping gives a good starting point for gritty monos.
And thanks for the question...
As far as "expose to the right" is concerned, remember it's only for RAW images. I don't know the various sources you've read, but I bet they weren't talking about RAW.
It's just a fact that in RAW most of a digital camera's sensitivity is in the right-hand third / quarter of the histogram. It can record far more (1000's) of subtle differences in light in that region than it does in the lh equivalent.
The upshot is that if you arrange for the area of most tonal interest to be exposed such that it is in that rhs of the histogram, you will record far more tones than if the histogram was a nice even hump across the middle. (But you don't want to blow the highlights, of course).
Oh, and I should say that if you just did that and nothing else to an image, it would be overexposed once converted from RAW. So during conversion, you have to bring the brightness down so that the "histogram" of the print image is once again a nice hump in the middle.
If that's not so clear, maybe if you think about it with an HDR head, it'll make more sense.
You've got a scene with some foreground rocks in deep shade and with gorgeous texture. The sky is a wonderful, filled with pre-storm roiling clouds -- but very bright in comparison.
Take one exposure of the rocks, exposed such that all its tonal detail is in the rhs bit of the histogram (where all the sensitivity to immensely subtle levels of light exists). Don't worry about the sky, the highlights can be totally burnt out.
Do another exposure, exactly the same but for the sky, making sure all the bright areas appear in the rhs bit of the histogram and no blown highlights. Note you will have no detail at all in the rocks - they will pretty much be in silhouette.
What have you now got? One RAW image with no tonal variation in the sky and with rocks from bright to quite dark, with oodles of subtle tones.
The other is the converse, loads of tonal detail in a sky going from bright to quite dark with only jet blacks for the rocks.
When you tone-map in HDR software, you're telling it to use the most tonal detail it can find. It looks to the first image for tonal detail for what are to become the dark regions, ignoring the brightest areas. It then reduces the brightness of all those tones to map them to what will become the dark areas of the finished image.
It does the converse with the second image, mapping the same areas of its histogram to the brightest areas of the final image. How does it know which image should be used for which bit? It is guided by the nominal exposure info recorded in the exif data (eg f11 1/125).
And of course it takes a middle of the road approach to the rest in the mid-range of both images' histograms.
What you have to remember with RAW is that in a strong sense, the exposure isn't really precisely fixed until conversion time, so even if it seems "overexposed" by having a rhs-biased histogram it isn't really. It'll only be overexposed in the final image if you don't adjust the "exposure" of the RAW file during conversion.
And just to be clear, you can afford blown highlights only if you're taking two separate shots, and then only in the one exposed for the darker areas.
Whew, now that was a lot of typing! I hope it makes sense :)
As usual, ask away if anything is unclear.
Cheers,
--Mark
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