Yogie's Photo PageFinally here is the video from our visit to Stonehenge in March….
Hint: Watch the video in HD!
Sep 052010
Jun 292010
Dynamic Range Increase (DRI) is a process within the modern digital photography to achieve a High Dynamic Range (HDR) photo. A HDR photo is a merge of a number of normal or low dynamic range photos. There are already HDR sensors and HDR cameras out, but they are quite expensive. The process of DRI, respectively producing an HDR photo can also be made with actual digital cameras and special software. I would like to give a short overview of my short experience with DRI and HDR photos and will introduce in one of my future articles some of the helpful tools that I have found.
Is there any reason to merge several photos into a HDR photo? Our human eyes are able to see 27 stops, a camera only takes a range of 5 stops when exposing a photo. This means that a photo when it’s shot mirrors only a very low range of the available contrast or has only a low dynamic range taken from the scene. The best example is a photo with a person standing in front of a window. While the human eye can see the face of that person and the things outside the window, a photo of that person normally shows only a shadow of the person. When the person is exposed correctly outside the window we only have a white or over exposed area. But how can we create an HDR photo to increase the dynamic range? Modern digital cameras can help us to create these multiple fotos, for example when they offer bracketing. So the camera will automatically take a photo which is correctly exposed and two other photos, one is under and the other over exposed – depending on your settings with a difference of one or two stops. As this process is time consuming and we certainly will move or shake the camera within this period, it is recommended to use a tripod to prevent movements as the photos have to be merged together in a later step and have to match exactly. The process of merging the photos together is called to increase the dynamic range. But even if you do not have a bracketing feature, you should at least be able to use a manual exposure mode and take the photos with different exposure timings on your own. I have expirienced that when having daylight conditions three photos are enough. At night you can also have more than three photos to be merged. In a future article I will introduce options on how to create a photo with a high dynamic range, but at first you need to have to shot photos as described in this article. So take a nice landscape for example and shot your photos using your cameras bracketing feature with over/under exposure of 1 or 2 stops difference, whether you should use a one or two stops difference is your own experience you have to make and depends on the conditions ony our set.
After taking your exposure sequenced photos, I’d like to introduce the first application to increase the dynamic range of a photo. The first tool is the Jasper’s DRIMaker. Today version 1.3 is up to date and it’s donation ware. After launching the DRIMaker you have the option to drag and drop your exposure sequence to the application.
Opening your photos via the menu didn’t work for me in this version. DRIMaker will automatically sort your sequence in ascending mode to the luminance regardless their EXIF information. I recommend to shot your photos with a tripod as DRIMaker will have to allign your photos to match exactly to each other.
After loading and aligning the photos you are now ready to use the threshold-slider to change the cross fade (transition) of the sequence, fine tune adjustments can be done by manipulating the other sliders for example the luminance-slider. There are no recommended settings – you have to try and play around with the sliders as any photo is different and anyone has own preferences.
You will see your result in a real time preview. You also can choose to see the preview in grey scale mode, quitting this needs a click on one of the sliders. With the zoom buttons you can zoom in and out, but sometimes the preview photo flips upside down – keep clicking and playing with the zoom and it will bring back the proper view.
At least to see the result in full resolution you will have to click the button therefore. At the preferences you are able to setup the format of the DRI photo that DRIMaker will use for the ongoing process of the DRI photo like sending it via mail or bringing your DRI photo to your iPhoto library – for the last two options you will find a helpful button. Via the menu you are able to save the DRI photo to your desired place regarding your format settings at the preferences. (Another button to save your photo would be nice to have).
At the preferences you will find an option to store your favourite photo editor, right clicking on the preview brings the option to load your DRI photo into your external program.
If you would like to proceed with another set of photos you simply have to click the reset-button and you can start over, but clicking the reset-button will not bring your sliders back to the starting position. DRIMaker over all makes a very good job, it’s easy to use and the result is a naturally looking DRI photo. Even to the very few bugs that I have found it is worth to support the author and donate his work.
Jun 292010
Photos with a high dynamic range are getting more and more popular and with that the range of upcoming terms and techniques is growing. But not all photos having a huge range of dynamic are HDR photos. I will follow up with these terms and describe the two main techniques to produce photos with a high dynamic range.
HDR
To produce a real HDR we need an exposure sequence. An HDR picture represents the tone values of each individual pixel with 32-bit per colour channel and in floating point notation. Therefore an HDR photo represents the entire tone value scope of a scene. An HDR file is thus a file, that by combining the dynamic range of any single photos out of our exposure sequence up to a photo with a real high dynamic range of 100.000:1 or more. HDR photos cannot be displayed on common monitors as they only offer a 100:1 to 1000:1 dynamic range to be displayed. So there is no way to manipulate or print such a file. To get an HDR to be displayed to a common monitor the high dynamic range must be tone mapped and reduced to a LDR Photo (low dynamic range). Nowadays there are two different tone mapping algorithms that have their own complexity. In general we divide into two groups: with the global operation the transition of any pixel is calculated by the luminance and the global characteristic of the photo. In opposite is the local operation that includes and considers the surrounding pixels for transition. Global operations can perform on computing time but with local operations the result is more realistic as the transition of the dynamic range increase is done locally. HDR photos are files that burst the display techniques we commonly use today. An alternativ technique to produce LDR photos with a high dynamic range is the dynamic range increase.
DRI
With the DRI process we also need an exposure sequence, but while creating an LDR photo with a high dynamic range, the exposure blending method will not produce or need an HDR file to work with. The exposure blending method will iteratively process the single photos of the exposure sequence. Starting with the most longest exposed photo out of the entire sequence. The brightest parts of the first photo will be softly masked and transited with the same parts of the next photo in the sequence. And then the process is starting again in the same manner masking the now brightest parts and transiting them with the same parts of the next upcoming photo. At any time there is no HDR photo that represents the complete dynamic range of the scene as the exposure blending is working only in a 8 or 16-bit RGB photo.
Jasper Grahl: http://www.drimaker.com