Sharpening with RAW Therapee-- Part 1

Let's start way back at the basics. What makes up the pic of your dog that you just brought up on your computer screen?  A very long list of numbers.

This is a small sample of the 5,161,117 numbers that make up my DSC8706 jpg   It's at the boundary between the header--the zeros at the top-- and the numbers that tells a computer how bright or dark to set the three colored dots that make up the pixels on its computer screen--the hexadecimal numbers at the bottom.

At the top of the header is the EXIF data--the list  of camera settings. Following that is more data about the lens I used.  Finally there are pages and pages of zeros that I could fill up with metadata. If I looked up the ascii numbers for 'This is going to be tedious!!' and individually replaced some of the zeros that sentence would show up in the metadata. If I still hadn't used up all my tedium quota for the day and replaced the picture data with zeros I would eventually draw a black line across the top of  DSC8706.

Once upon an ancient time that was how data editing was done.  And shortly after that ancient time, when monitors that could draw pictures appeared beside humongous CPU units, programmers began writing image editors to take away the tedium of doing such mathematics on these lists of numbers.
 
Sometimes we only want to modify a pixel or two--covering up hot pixel noise--but usually we want to do mathematical operations on all or a good part of our image.  For example, to increase the effective exposure by a stop we multiply the image numbers by 2. Or to decrease it by a stop, we multiply by 0.5. Or we multiply them by a range of numbers that depends on how far and in what direction we drag a point on a tone curve.

To sharpen an image with an unsharp mask we do "a simple linear image operation—a convolution by a kernel that is the Dirac_delta minus a Gaussian blur kernel."  As per  http://en.wikipedia.org/wiki/Unsharp_masking

All clear and understandable?  Right?  Or did you party big time the night before that early morning math class and  could use a refresher explanation? Maybe you even forgot how you sharpen an image with, of all things, an unsharp mask.

Unsharp masking goes back to a time when you would stick your head under a big black cloth and take your image on a large single sheets of film.  Once you developed  your image of a black bird flying up in the light blue sky, you would have the B&W negative, a white bird in a black sky. If you projected this on another sheet of film, after development you would be back to a positive, a black bird against a lighter sky. If you did this as you would with a print, well focused, you would now have a  'sharp' mask.

Which wouldn't be much use. Instead. if you defocused your enlarger you would have a blurry and wider positive of your black bird, your 'unsharp' mask.  When you carefully aligned the original negative and its mask and put the stack in your enlarger you have a halo around the edges of the black bird. This combination will make a print with more edge contrast than a print made with just the original negative. There isn't more detail but because of the way our eye/brain system works this print will look sharper.

Back in those film days this was another  'great in theory' procedure that hardly anyone ever used.  It wasn't until our digital days when all you had to do was move a few sliders to  ' convolute them sharpening kernels' that it became part of a photographer's digital development work flow.

Since a quick google of  'unsharp mask tutorial' will show why the world doesn't need another unsharp mask tutorial, I will talk about what happens when I go out my way to do it wrong.

Instead of a blackbird I start with a seagull flying over a field and pond--a peaceful and quiet country scene. (Which it ain't. The second largest mall and one of the busiest intersections in the city was behind me.  A tidbit of info I'll toss in to point out that in photography framing may not be everything but it is still is a good hunk of everything.)

I ran the unsharp mask sliders up as far as RT would let me before I decided that image would be too ugly even for this do-it-wrong tutorial. So I pulled them back slightly.

Usually I see white halos when I over-sharpen, but that is because nature gave us far more darkish subjects than pure white subjects to photograph. The bird's white head has a well defined black halo while its black feet has a more traditional white halo. In the third window where there isn't much contrast between the upper part of the inner wing and the soccer field the halo is barely visible.

Traditional versions of unsharp mask have only three sliders--radius, amount and threshold.  RT's version has five--Sharpen only edges and  Halo control. Sharpen only edges work to prevent the sharpening of noise noise pixels. I'll go into that in another tutorial.

Activating halo control didn't completely eliminate the halos, I'd gone too far with the other settings, but it did reduce them considerable. With more normal setting, a radius of 0.8, an amount of about 150 and the default threshold of 512 I doubt I would have had to use halo control.

In the end how did I sharpening the image? By using only the contrast by details routine, a feature not found in other RAW (or jpg) converters.

What this routine does is use some fancy math to select areas that have details. The areas range from 1 or 2 pixels wide (Finest) up to about 16 to 20 pixels wide (Coarsest).  Then RT multiplies those areas by whatever number you select to make them stand out in the image. Or stand out less in the image if you move the slider towards zero. With a high ISO images, one to two pixel areas are almost always noise spikes. Then I set the Finest slider down to around zero.

As with all sharpening routines it is easy to get carried away. With flower macro images setting the numbers 1 and 2 slider to slightly under 2.0 works well.  With this image which has motions blur I went a bit farther in what I must confess is a rescue operation.

I was driving out of the parking lot of my bank when I spotted the seagull.  I had my camera in the back seat but didn't have the time (or forgot) to set the camera up for bird shots. I snapped this image at 1/500 sec instead of a motion stopping 1/1200 sec. While RT can and has hid many of my photographic mistakes, with motion blur it can't perform miracles.

And don't be surprised if RT slows down. It's one of RT's most CPU demanding routines. With 16.2 mp images and using a less than a speed demon, four year old, 32 bit machine it add a minute or so to the RAW conversion  But you will find the extra time worth it.

The top window is with sharpening, the bottom is without.

So, grab your camera and best birding lens and go off for the image that will wow the world.  RT has all the power you need.  The rest is up to you.

RAW Therapee As a JPG Editor Part1

It was the Raw in RAW Therapee that attracted me at first. Then, as I said in the last post, I wrote a tutorial for a flickr contact who underexposed her vacation photos. That sent  me deep into the archives to my P&S days when I could only shoot jpgs. Which brings me to this post, a look into the unique RAW Therapee features that other jpg editors, free or pricey, lack.

I shot this in 2007 at a summer tradition--the Madison Symphony pop concerts on the Capital Square. My son who had moved into an apartment off the square invited me to join him and some friends for a picnic and music.  Both the food and the company were excellent, but they had laid out their blankets away from the crowd.  So I couldn't see the orchestra which limited my photo opportunities.

But that changed. During the intermission as the sun was setting and the light had become golden this girl began to crawl on the railing in front of us. During my fresh look at the photos--after four years I forgotten I'd taken them--it was the staircase in the background that first caught my attention.  If I could brighten the girl slightly, or conversely darken her into a silhouette, plus make the staircase more golden I might have an image worth posting.

As expected the first slider on the exposure tab, exposure compensations, brightened the girl but killed the staircase. It moves the white point of a RAW file, the value RT set to 255, 255, 255 when it create a new jpg. With just a jpg saved in the archives that data disappeared 4 years ago the instant I press the shutter for the next photo. Not useful for this task.

For a darker silhouette version the black slider was more useful

By moving it up from 0 to 9600 I closed a gap in the histogram to darken the girl. Moving the Brightness slider up to 20 lightened the staircase but at the cost of the golden color I was looking for. Ok but not what I was after

To get the image I wanted I turned to the RT tone curves.

The first tone curve on the tab works with the RGB data. It lightened the girl nicely but eliminated the golden light on the staircase.  By pulling the curve up I changing how bright the Red, Green and Blue dots that make up the  girl pixels would be on yours and my monitor.

RGB tone curves introduce color shifts. Depending on what you are after this might or might not be a problem. For instance, if I had wanted to restore the original white color of the staircase, the color shift would have been an improvement.

RT's second tone curve at the bottom of the tab works with LAB data. It's a tone curve I've not seen in any other RAW convertor or jpg editor.

LAB stands for Luminosity, A and B channels where the L channel has all the brightness data, the A channel has all the red and green data and B the blue and yellow data.

Or if you aren't interested in the LAB color theory stuff--I have a thick book just on how and when to use the LAB mode-- the one thing to remember is that RT's second tone curve works only on the Luminosity channel. It doesn't touch the color information. So no color shifts ever.

With this conversion, besides brightening the girl with the tone curve and the brightness slider I added a bit more saturation to make the staircase stand out more against the different granite in the capitol walls.

The flickr posted version after I used RT's straightening tool to hide my habit of never getting the horizons, real or virtual, level.

As for the other tabs, Highlight Reconstruction is greyed out since it works only on RAW data during the demosicing operation. It does a great job too but it doesn't fit into this post.

Shadows and Highlights does work. If you want to use it conservatively as high end image editors such as Photoshop forces you to do, I'll refer you to Paul's excellent and readable manual. It now ships with your RT downloads and is also available in the documentation section on the RT website.

But if you are in a 'fun&crazy' mood try this.

Our girl once she found a spot to sit.

And after I ran the exposure comp up around 6 to drive almost everything into saturation and then played with the Shadow/Highlights tab to see what would happen. Try it on your own images. It's fun.

RAW Therapee's Batch Processing to the Rescue

Autumn, a long time flickr contact, had a problem. During a vacation trip to Florida two years ago she went sailing and took a pile of photos with her Coolpic 550s P&S. Unfortunately her camera was accidentally setup with an EV of -1.7 and all her jpg pics came out ~4X underexposed.

Batch processing is not a new RT feature but until recently I hadn't realized how powerful and useful it could be.  I've taken my share of images with a setting wrong--white balance, exposure, etc--before I noticed and corrected it. So here is a mini tutorial using some of Autumn's photos on how I would use RT to hide these mistakes.

Start RT in its normal multi-tab mode and open the folder with the underexposed photos. Start by upping the exposure  +1.7 in one of the photo using the Exp Comp slider. Name and save your new profile.

Go into the file browser and control click on the other underexposed images.

Right click on the selected photos. This will bring up the new batch interface. Click on Profile Operations, Apply Profile, and in this case Autumn Underexposed, the name of profile I just saved.  Your copy of RT has a profile folder that holds all the default profiles that come with RT plus any you created and saved.

After a few seconds the thumbnails will brighten up. What have you done? Like Adobe Lightroom you haven't changed any of your photos. Instead you have created a pp3 file for the photos you selected which tells RT what changes you want to make.

What's next? If exposure correction was all you wanted to do, you could hit ctrl Q to put them into the Batch Queue. After selected what folder you want to save them to and the desired file format--jpg, 8 and 16 bit Tiff or PNG--you can hit start processing and let RT do its thing.

I preferred to fine tune the three photos I was working with.

The horizon was tilted, always happens with rocking boat photos, so I corrected that with the straighting tool  The overall photo was now exposed correctly but Autumn and her sister Jordan--wild hair--were still too dark. I used the LAB mode luminous channel on the Exposure tab to create a tone curve. I could have done this with the more common RGB mode but I think the LAB mode is cleaner since it doesn't introduce color shifts. Beside LAB mode editing on a RAW file is one of many features unique to RT. I also noticed that parts of the T-shirt were blown out so I use the Highlight Recovery slider to correct that problem.

After I finished editing the photos I put them into the batch queue.  There are two versions of the air plane image, each with different editing. Once I convert them I'll view them full size and decide which one I prefer. It's a great timesaving feature and a few days ago I converted the same photo 14 ways in one operation to check out the new profiles that showed up in the latest build of RT.

Although it wasn't necessary since I have 4GB of memory on this computer. I also closed everything but the batch queue and file browser.  If you look close, I forgot to circle it, you can see where the memory usage dropped in the Windows Task Master window.  RT can do many great things very well but that requires more RAM memory than the less useful free (and expensive commercial) editors. So if you have an older computer watch your memory usages.

How many great things can RT do very well? Here is the current list

If you click on Apply Profile (partial) you can pick what features you want to use from your saved profile. It is also a great overview of what RT can do

Finally I must thank Autumn for letting me use her photos in this tutorial.  You can find her flickr photostream at  http://www.flickr.com/photos/syksylla/