Part 1
Part 2
Part 3
Part 4
Part 5

Part 2 - Stitching

In part one I walked through capturing all of the exposures to build this image. If you've landed here first please have a look at the previous page to see how I got here.

Sheas 06

Those 63 exposures I made in part one contain a lot of image information. They are sort of like puzzle pieces right now as each one is a fragment of the larger image. Now I need to combine them into a set of bracketed images with each one containing the entire scene.

The application I use for stitching is AutoPano Giga from Kolor Software. If you go to Kolor's website you will see the application is targeted at creating panoramic images. The technique here is really just a variation on the full panorama. I guess you could think of this technique as cutting a section out of a larger panorama.

Autopano can use source images in many different formats including RAW but I like to convert my RAW files to uncompressed TIF first. This allows me to use the RAW converter of my choice rather than relying on the built in converter. Not that the built in converter isn't good but I have really come to like the quality of conversion in Adobe Lightroom.

 

 

 

 

 

Import into Lightroom

Plugging my flash card into the reader on my PC automatically launches Lightroom and shows the images on the card. I have Lightroom set up to download all the images into folders sorted by date on an external RAID drive.

 

Adjust the image parameters

Noise

With all the images downloaded to my drive I now want to examine the normal exposure frames to see if they contain any excess noise. I was using a tripod and in theory could have set my ISO to the camera's native 200 but there was a small problem with doing that. If you remember I was taking bracketed sets letting the camera adjust the shutter speed automatically. On the D300 the longest shutter speed that can be set automatically is 30 seconds. With the aperture I selected if I had used ISO 200 then my longest shutter speed would have fallen outside the range. To bring all the bracketed exposures in range I bumped the ISO up to 800.

Noise Noise Reduced
Noise reduction

 

On the D300 ISO 800 is really the highest I like to go. At 800 I can recover the noise in Lightroom easily without destroying image detail. Above 800 and I can detect loss of image quality. I have tried Topaz Labs Denoise and it also does a great job but it means the extra step of batching in Photoshop. The point of all this work is to produce the highest quality images so I avoid high ISO whenever I can.

I don't want to get too hung up on the image noise here because this will be a 90 megapixel image and when printed even at 20 x 24 inches the noise is really not going to objectionable and I'd rather have a small bit of noise than a plastic image.

What is important is that the process of combining the brackets into HDR can potentially create serious noise problems. So if you have objectionable noise at this point you should experiment to see how much needs to be removed so as not to cause problems in the HDR merge.

For Noise Reduction I left the default of 25 for color. I bumped the luminance slider up to 20 and the luminance detail slider to 70. That's all I felt was required.

White Balance

When I shot these images I included a gray card so that I could later set the white balance accurately. This is a snap in LIghtroom. Select the white balance tool and click on the grayscale. For this image setting the correct white balance actually kind of destroyed it. A big part of this image is the ambience of the scene. The dim lighting and the strong unnatural colors. Correcting the colors stripped away the feeling. I'm going to convert this to Black and White and in this case the strong color casts actually help. The strong saturated colors are great when you use the Black and White tool in Photoshop because they create separation in the image. I decided to leave the white balance as shot.

Exposure

I left all the exposure settings to the defaults because I will be combining the images in HDR. No need to alter the tonality here.

Clarity

I always bump the clarity slider up a bit. For this set of images I used 16.

Sync

That was the extent of my parameter adjustments in Ligthroom. But before the final export I synched the parameters for all the images in this set.

the final task was to export the set of images as 16bit TIF files. In my workflow I create two folders for each image I plan to stitch. One folder for the source images and another for the rendered images.

 

Stitching in Autopano

The next step is where things start to come together and I can see if all this work has paid off or if I forgot something important and have to start over again. I start up Autopano and load my image set.

Autopano
Autopano Giga

After the images are loaded I like to set the detection parameters and turn off lens correction. I find that this gives me better results when the focal length is 50mm as there is very little distortion in this lens at this setting. I limited the detection to one image stack level and pressed the start button.

After detection
After detection
Bracketed Layers


This is why I love Autopano. In just a few seconds it analyzed 63 images, found the matching points and aligned them into a single image.

Sometimes the stitching process does not produce the desired results on the first try. At this point Autopano has tools to help you fiind and correct any problems but the RMS of 2.30 indicated shows I have a really good stitch and I'm not going to get much better.

Notice that the shape of the stitched image is a bit concave on the sides. That is an artifact from rotating the camera and not a problem with the image. I'll crop later.

There is only one more thing I want to do before the final rendering and that is to tell Autopano that I want a separate output file for each of the brackets.

Clicking on the bracket button separates the images and creates a new layer for each of the seven brackets. You can see the seven layers and their associated EVs to the right. This is a very important step and if you forget to do this you will wind up with one output file that is Autopano's attempt at combining the different exposures. In the next part I'll be combining the seven output files into a single HDR image.

 

 

Output Dialog

 

Clicking the Render button presents a dialog with options for the output files. You can scale the final renders but I'm going to leave the output to 100%. I will leave the defaults for Interpolator and Blending type as they always work ver well for me. Smartblend can be a little slow and requires a lot of disk space but I like the results.

I prefer to keep my images in 16 bit so I will set the format to TIFF and the depth to 16bit and check one output layer per file. I set the destination and click the Render button. This part of the process takes a bit of time but when it is done there will be one 90 megapixel output file for each of the seven brackets.

In the next part I will combine them into a single HDR.

 

 

 

 

 

 

 

Links:

AutoPano Giga - www.autopano.net

 

 
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