Jpeg quality comparison

To my shame I notice that I neglected to link earlier to this excellent analysis by Jeffrey Friedl on the effect of the jpeg quality setting in the Lightroom export module. If you use Lightroom and export images to the web, it would be well worth your time to read this article and check out the comparisons.

On output sharpening

Lightroom 2.0 includes new output sharpening facilities in the export dialog, the print module and the web output module. These are extremely useful. The functionality is to correct for softness induced by the scaling for output and for the softness of the output medium such as a screen or a printing process. Here I'll talk about the use for output images for the web, email, etc. I used the export dialog scaled to 600 points for the long dimension and selected different levels of "screen" sharpening. Here is an example of a waterfall image. See (and buy prints of ;-) )the real image here. You can switch between different output sharpening levels by hovering over the names on top.


unsharpened
low sharpening
standard sharpening
high sharpening


To me, the difference between no sharpening and even just low sharpening is night and day. In the lychen details on the wet rocks for example. You wouldn't notice probably if you just have two images in different contexts, but you would probably thin-slice prefer the slightly sharpened one. The high sharpening is still very good in my opinion and works well for this image.

Here an another example of a cliché truck. This image has lots of sharp detail and you'll see that going to high has a different effect than on the waterfall image.

unsharpened
low sharpening
standard sharpening
high sharpening


Notice the extraordinary amount of extra detail that is pulled out in the hood area by the sharpening. This time, I think high is over the top and the best is probably low or standard. This is quite generally true for images that have man-made structures that have very sharp transitions. In general I have found that using standard gives very good results for most images, but of course this all depends on your taste.

ISO noise quantified

Warning: geek content!

In my previous post, I looked at noise in bokeh areas on my D300. You can clearly see some noise at ISO200 in darker out-of-focus areas on that camera. At the end I showed that the noise is quantified in the jpeg filesize. Being the science geek that I am, I did a quick analysis on it. Here is the filesize plotted vs the ISO rating:



The red curve shows a fit to a simple square-root dependence on ISO. This is not just some arbitrary choice. If the noise is coming from simply photon-counting statistics, you expect approximately a square root dependence of the signal-to-noise ratio on exposure time. In this case, this means that the absolute noise should also scale with the square root of the ISO rating. Indeed, you can see, barring an offset of 129 KB owing to the fileheaders and the actual scene information, there is a square-root dependence of the filesize on the ISO speed. Interestingly, since the jpeg encode is a visual compression scheme, this should correlate with how visible the noise is as you could clearly see in my previous post. Also, at ISO 100, the amount of noise is indeed almost negligible as you can see from the negligible difference in size between the ISO 100 jpeg (144 KB) and the limit at (the impossible) ISO 0 of 129 KB.

Now there are some issues here that I have not addressed. 1. Lightroom might be doing more noise reduction at higher ISOs than it is at low ISOs, and 2: Jpeg filesize does not linearly correspond to the amount of noise. This is a toughie!
So you should just take this for what it is, despite appearances, rather unscientific! I do find it intriguing however, that the metric clearly seems to scale with visible noise and that the metric seems to indicate simple statistical noise, meaning that the amplifiers in the camera do not seem to introduce much noise at this light level.

Great prints from labs

Earlier I wrote about a workflow to get beautiful prints from labs such as costcos using Lightroom and external apps. In the new Lightroom 2.0 beta, Adobe has heard our prayers and the print module (unfortunately still not the normal export) now allows output to jpeg in arbitrary color profiles. This works beautifully.

Here is an example setup: (click for full size)



I set up a custom paper size in the page setup panel for 5x7 images without any margins, and setup the image in the print panel. Then I select print to jpeg, set the resolution to 300 (the resolution most Frontiers and Noritsus print at), set print sharpening to the paper kind and desired sharpening (I've found from testing that low or medium works really well even though these settings are not really meant for photographic lab printers). Then in the color management tab I select the profile from my lab (my local costcos in this case) and what kind of rendering I prefer. Then hit print to file and I get a jpeg file with the right profile and size/resolution/sharpening that I can upload and print (don't forget to turn off color correction for printing your images otherwise all your hard work is for naught). Very handy. Unfortunately, multipage jpeg output is still broken in that it gives you a set of files without extensions. They are normal jpeg files though. Also, there should be an option to not include the profile in the output file. Often these profiles are gigantic (my costco one for example is 1.5 MB) and they add substantial time to the upload to the lab. I usually strip them using a photoshop droplet, but this could be much handier. Also, there still is no softproof here anywhere.

Anyway, here is the result of such an exercise with the slide image after conversion to sRGB for web display and scaling/sharpening for display.


Enjoy your prints. Note that you should not bother with any of this if you do not calibrate your screen using calibration hardware. Screen calibration is the first requisite for getting good color prints. Secondary to that is using lab printer profiles. With an uncalibrated screen - no matter how expensive - you will never see the correct color anyway.

New camera

A recent mishap where somebody drove their car over my backpack containing my camera, breaking the lens out of the mount (luckily a plastic lens) and breaking the command dial (making the camera rather useless) made me realize I need a second camera. I usually borrow or rent a second camera for events but otherwise have been very happy with what I had, even if it was only a 6 MP machine. For landscapes I would often use film anyway or stitch multiple images together and the very sharp 6MP allowed for surprisingly large blowups (I've gone to 20x30 and they still look great and surprisingly sharp). Anyway, since there is a great deal from Nikon that is active on Adorama, B&H, ritz, etc, where you get $300 instant rebate on the D300 together with the 18-200VR, I went for it. Note that Adorama has already run out of them in just a few days! This camera is astonishing. I used the D200 and Canon equivalents, but this camera beats most of them in use and feel. I wonder what a D3 would be like? Next to being great in use (the AF system is a dream), it is sharp to the pixel (at least in RAW) and that screen is superb. Also, its jpeg engine is astonishing. I was playing around with it yesterday and shot this mêh scene of a child's slide on our deck. I am astounded by the color. Especially since this was pretty boring hard light.



That's straight (except for scaling and sharpening for the web at a larger size than you see here (follow the link) by LR2 beta) out of the camera. Some more here:







Now you have seen a lot of the silly stuff in our garden ;-)