Hi Will,
Wikipedia has an article: Chromatic Aberration

It's not just digital - it's primarily down to the lens where different wavelengths (ie colours) of light bend at different rates within the lens.

It's often most visible when you have backlighting - but it's always there and if your lens suffers from CA, then correcting it will improve overall sharpness for other images as well

If you shoot RAW, and use Silkypix then that has CA adjustments which can pull the red/green or blue/yellow back into alignment. In SP-DS3 it's the button to the left of the rotation control - it looks like an hourglass figure.

Zoom in to 100 or 200%, and adjust the "R" rate - that's Red/Green.
If you have blue or yellow CA, then adjust the "B" rate.

(In your example, an R rate of +9 looks about right )

Just tweak it very slowly (use the arrows rather than grabbing the slider) and you should see the effect of the adjustment.

Matt

Will - you've got some serious CA on the left tower. Use the lens adjustment tool in SP-DS3, zoom in, and slowly adjust the CA controls until the red and green converge. (But be sure to check both sides of the image, because you can't always get it perfectly.)

If you can't align in SP-DS3, then try the following in Photoshop:
* Add a new layer
* Change the layer blend mode to "Color"
* Pick a small soft brush, set at 50% opacity
* Alt-click on an adjacent area to pick up the colour, and brush over the CA
* Repeat as necessary

That will keep the luminosity, but reduce the glaring red/green

HTH!
Matt

I think it depends on the kind of shot. Don't forget as well, that white balance and colour profile will have an effect on the histogram as well as exposure

I'm finding that I often have to increase exposure by up to 1 stop - but again that could be down to the combination of lens & scene.

The general way of working with RAW in SPDS3 is:
1. Adjust basic exposure
2. Adjust white balance
3. Tweak contrast
4. Select colour
5. go back to 1 if necessary and loop until happy
6. Adjust sharpness and noise reduction
7. Output

In any of the steps 2-4 you have to keep an eye on the histogram to see where the levels are and go back a step or two until you're happy.

For really rich colours, try pulling down the gamma slightly, and possibly up the contrast a touch (e.g. this image - no polariser, just SPDS3)

Matt

(I plucked the 24-bit ADC out of Google just to show that 22-bits isn't really a big deal, even at data rates. BTW, I seem to remember that the larger CCDs have multiple modes where they can bucket-chain out the values in 2 or 4 channels to increase data rates... but that may not be on the K10D)

Beg to differ on this point - the CCD is actually 3872x2592 light values - not RGB pixels. The pixels are arranged in a four square bayer matrix (R/G/B/G). So, the figures are a factor of 3 too large The RAW conversion (either in camera or on PC) has to demosaic the image to get a full 3 primary colours per pixel.

I certainly agree that the lower bits of the ADC are almost certainly just noise (and it won't be 5v, most certainly 3.3v).

However, think about it this way - assuming that there is no variable gain pre-amp between the CCD and ADC - there only needs to be a 5 bit range over and above the image range. So, assuming the usable image range is 12-bits, then 17-bits will cover 12-bit image over a 5-stop ISO range. (Since each ISO step is a doubling in intensity, and therefore one bit in binary.)

My point was, not that I'd need all 22-bits, but they might as well create a RAW format that dumps the lot anyway so the software can make decisions about the noise floor and we'd get a near-HDR single image that covers at least 5-stops more than the current single RAW frame

(Like other manufacturers you can always "gang" the pixels together for the very low light and reduce the effective pixel count.)


So, we'll just have to wait and see
Matt

True, you don't. I know my electronics I shalln't bore you with the projects I've worked on, but believe me...
e.g. http://focus.ti.com/docs/pr/pressrelease.jhtml?prelId=sc05240

I based my assumptions on:
1. The fact that 22 bit ADC are not a problem at all in modern electronics
2. There was a video interview/transcript with one of the designers/managers of Pentax Japan who said they were aiming at reducing the number of electronic stages between CCD (which is analogue) - hence my comments about removing the amp (at least simplifying it).

At the end of the day it doesn't matter at the moment... the K10D produces a wonderfully clean image. But I reckon that a larger RAW file will happen sometime (even if it's "only" 16-bit)

Matt

Not exactly
Pentax cut down on the number of stages from the CCD to the ADC. Normally you'll have an amplifier to set the ISO rating between the CCD and ADC. From what I gather, Pentax have no intermediate amp and so the ADC sees the full dynamic range all the time (ie all the ISO ratings).
When you set the ISO rating, you specify which range of values should be taken from the ADC and saved in the 12-bit RAW file.

So, if you had a "full" RAW, then you'd cover a much larger dynamic range You would expose for the highlights (ETTR), but the 22-bits should give a much deeper shadow range. (But you'd have problems with processing it, and you'd still need to tone map it )

Your estimation is probably around about right with the current RAW files. I reckon I get a bit more out underexposed... but maybe only another half stop. There's no excuse for at least trying to get the right exposure
Matt

Pete,
Well, not exactly recommend. Personally I don't think any of the software is 100% right now. But to get you started here are a few links:

Artizen: http://www.supportingcomputers.net/ - good, but excruciatingly slow, even with a seriously fast machine.

Photoshop CS2 - has HDR support. Fairly poor at combining the images unless they are 100% the same (just different exposures). Artizen is much better at assimilating the images. Tone mapping is pretty good, but takes a lot of practice.

Photomatix: http://www.hdrsoft.com/ - Their tone mapping isn't as versatile as Artizen. It's a touch faster, and combines images well (even with people moving etc). Didn't like my K10D DNG files though - produced some very strange artifacts! Their website has some examples (which I don't like personally!)



Just bear in mind that most of it is very experimental. There are many, many tone mapping algorithms available - all work with different image types. The other thing is that we perceive prints differently compared to web images - so an HDR print may look really excellent, but a bit "neurgh" on the web

Matt

HDR = High Dynamic Range
HDRI = High Dynamic Range Imaging.

It involves a few things:
1. Taking a series of bracketed exposures (on a tripod). Say, -4EV, -2EV, 0EV, +2EV, +4EV (that's four stops underexposed, two stops underexposed, "correct", two stops over, four stops overexposed)

2. Combining the set of images in software into an HDR image file. This is 32-bits per pixel (ie 16million times greater range than a JPG). The HDR image contains a wider range of dark to light than can be represented on any monitor (e.g. the shadows to the brightness of the sun)

3. Doing any adjustments on the HDR file

4. Then mapping the information contained in the HDR file down to a "normal" image. This is called "tone mapping" and is where the "unrealistic" component creeps in.

Here are two "pro" examples:
http://www.ephotozine.com/gallery/showlargepic.cfm?photoid=804864
http://www.ephotozine.com/gallery/showlargepic.cfm?photoid=814571

Note that you could never normally obtain both the streetlamp and the shadows... not even with a filter

It's complex, tricky, and at the moment a complete pain in the neck!! But I find it's an interesting challenge...

Hope that helps!
Matt

George,
Fair comment I was in a "graphic" mood at the time

Of course, you can apply an easier technique by taking one or two shots, 2EV apart and manually blending them in Photoshop with layers. Saves lugging around filters (which are expensive with the 12-24mm).

In fact, most of the tone mapping can be done manually in Photoshop - and I have a shot that just won't tone map properly. May have to resort to manual blending anyway

Now on a similar topic... I really, really want Pentax to add full 22-bit RAW to the K10D and Silkypix. That'll add some serious dynamic range and save most of the messing around with HDR so it can still be a "photo"

Matt

HDR - yup

It can be used or abused. There are actually two things to HDRI:
1. HDR
2. Tone mapping

The HDR is where you grab several frames and software splices them into a single 32-bit per pixel image.

The tone mapping is where it goes pear-shaped and unnatural. Many examples over do the TM and make it painting-like (which is fine if that's what you want).

Yes, it needs shed-loads of RAM and CPU power (I have a 2Gb Pentium dual Xeon, and it's slow even on that )

Here's one I prepared earlier:
http://www.ephotozine.com/gallery/showlargepic.cfm?photoid=815867

Hopefully it's not immediately apparent that it's HDR
HDR is an emerging technology, and there's lots to be learned. It has its uses

Matt