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Most of you may be now familiar with HDR or High Dynamic Range in games. HDR enabled games look amazingly lifelike with better lighting and shadows and the clouds look ultra-realistic. What actually makes HDR images different from traditional images is the fact that they have a higher range of intensity levels (this article is meant for a layman and we are therefore not using technically correct words like Radiance and Luminance), and it is more like the way we perceive through our eyes.
Digital cameras are cheap these days, and you get image quality that rivals that of SLRs of yesteryear. But if you observe closely, there is still a lack of realism in the images that are obtained by these digicams. The problem is that the CCD is simply unable to capture the complete range of intensity of light in an image at one shot. An example of this is that the shadows are not dark enough, highlights are not bright enough or at times are too bright, and then there is the loss of perception of color of the light source. This is where HDR photography comes into play.
In HDR photography it is possible to capture and display the complete range of intensity of light and color that makes the photographs look lifelike with a richer contrast that doesn't look artificial (usually). Contrary to popular perception, HDR photography does not require an expensive digicam. Even entry-level cameras, which allow you to set different exposure levels or shutter speeds, can do a good job. All you need to do is take photographs of a scene with different exposure settings. If your camera supports Exposure Bracketing, then select the Continuous Shooting mode with the camera set to Aperture Priority and select an exposure increment of +/-2. The camera will automatically vary the shutter speed each time the shutter button is pressed and vary the exposure. The larger the number of photographs and the larger the exposure difference, the better will be the results you get.
The most common technique for HDR photography is to shoot a number of photographs of a scene using different exposure settings. Thus, some photographs are underexposed, while some are overexposed. The underexposed photographs capture the details in the lighter and reflective areas better, while the overexposed photographs capture details in the darker areas. These images are now combined into a single image, taking the better things from each image, thus resulting in an image that contains a larger range of light intensity. This method is known as Exposure Blending and there are several programs available that can do it.
Since HDR images contain a huge amount of data and it is not possible to display it as it should actually appear on conventional CRTs and LCD monitors, a method known as Tone Mapping is employed. Tone Mapping attempts to compress the entire dynamic range of light intensity into a viable range that can be displayed on the above display devices. This produces an image that retains realistic color and contrast.
Digital cameras are cheap these days, and you get image quality that rivals that of SLRs of yesteryear. But if you observe closely, there is still a lack of realism in the images that are obtained by these digicams. The problem is that the CCD is simply unable to capture the complete range of intensity of light in an image at one shot. An example of this is that the shadows are not dark enough, highlights are not bright enough or at times are too bright, and then there is the loss of perception of color of the light source. This is where HDR photography comes into play.
In HDR photography it is possible to capture and display the complete range of intensity of light and color that makes the photographs look lifelike with a richer contrast that doesn't look artificial (usually). Contrary to popular perception, HDR photography does not require an expensive digicam. Even entry-level cameras, which allow you to set different exposure levels or shutter speeds, can do a good job. All you need to do is take photographs of a scene with different exposure settings. If your camera supports Exposure Bracketing, then select the Continuous Shooting mode with the camera set to Aperture Priority and select an exposure increment of +/-2. The camera will automatically vary the shutter speed each time the shutter button is pressed and vary the exposure. The larger the number of photographs and the larger the exposure difference, the better will be the results you get.
The most common technique for HDR photography is to shoot a number of photographs of a scene using different exposure settings. Thus, some photographs are underexposed, while some are overexposed. The underexposed photographs capture the details in the lighter and reflective areas better, while the overexposed photographs capture details in the darker areas. These images are now combined into a single image, taking the better things from each image, thus resulting in an image that contains a larger range of light intensity. This method is known as Exposure Blending and there are several programs available that can do it.
Since HDR images contain a huge amount of data and it is not possible to display it as it should actually appear on conventional CRTs and LCD monitors, a method known as Tone Mapping is employed. Tone Mapping attempts to compress the entire dynamic range of light intensity into a viable range that can be displayed on the above display devices. This produces an image that retains realistic color and contrast.
We shall now explain how you can actually go about getting an HDR image using a free program called Qtpfsgui (and optionally also using GIMP or Photoshop). Qtpfsgui can be downloaded from http://qtpfsgui.sourceforge.net/download.php. Do not forget to download the DLL package also.
You need to have at least three photographs of the same subject with different exposure: underexposed, normal exposure and overexposed. You can achieve this by either varying the EV settings on your camera by setting it to EV-2 (underexposed), EV 0 (normal exposure) and EV+2 (overexposed). Or if you have a camera that allows you to set shutter speed, you can set the shutter timing to 1/500s for underexposed, 1/25 second for normal exposure and 5 second for overexposed.
If you are working with RAW images, it is a good idea to use noise reduction facility in your image editing software for each of the images before proceeding to the next step. This is because the tone-mapping procedure introduces some degree of noise in the resultant image and if the noise is reduced at the start, then it will be lower in the final image as well. With the photo set ready, you can now proceed to create an HDR image using the software.
1. Download and install Qtpfsgui and also extract the DLL package to the same folder where you installed the program.
2. First click on the New HDR button. In the next window that pops up, click on Load Images button and choose the three photos you prepared.
You need to have at least three photographs of the same subject with different exposure: underexposed, normal exposure and overexposed. You can achieve this by either varying the EV settings on your camera by setting it to EV-2 (underexposed), EV 0 (normal exposure) and EV+2 (overexposed). Or if you have a camera that allows you to set shutter speed, you can set the shutter timing to 1/500s for underexposed, 1/25 second for normal exposure and 5 second for overexposed.
If you are working with RAW images, it is a good idea to use noise reduction facility in your image editing software for each of the images before proceeding to the next step. This is because the tone-mapping procedure introduces some degree of noise in the resultant image and if the noise is reduced at the start, then it will be lower in the final image as well. With the photo set ready, you can now proceed to create an HDR image using the software.
1. Download and install Qtpfsgui and also extract the DLL package to the same folder where you installed the program.
2. First click on the New HDR button. In the next window that pops up, click on Load Images button and choose the three photos you prepared.
Qtpfsgui will try to automatically determine the exposure value from the EXIF metadata in the image, but if it fails, then you will get an error message and will have to specify it manually.
Select the Image Filename on the left and set the EV value for individual images using the slider in the right hand side of the window.
3. Select the Auto Align Images checkbox so that the program compensates for or corrects any misalignment in the consecutive shots. Let it be set to "hugin's align_image_stack". Click on Next and skip the next window, which is the Editing Tools window, as it requires some practice to modify anything here.
4. Skip the next window too, where there are a number of predefined profiles to choose from, which give you slightly different results. Let default option remain chosen here and click Finish. The next window will show you the raw HDR image, but this is not our final result. This still requires tone-mapping so that it can be displayed correctly in a low dynamic range image format (jpg).
6. Now click on Tone-map HDR button in the toolbar. A window will pop up with a number of tone mapping algorithms and parameters.
7. Now choose Fattal tone mapping operator and increase the Noise Reduction slider to a value between 0.05 and 0.5 and reduce the Beta slider a bit. Click on the green button Apply. You can try changing the values a little to get better results.
You can fine-tune the result by clicking Adjust Levels button. After you are satisfied with the results, save your image file by clicking on Save as button at the top. Make sure to choose the Result size as the same as the size of the original image while saving the final image.
8. Now choose the Drago tone mapping operator tab and repeat the procedure in the previous step. You should finally have two tone-mapped JPG images.
9. Open both the tone-mapped images in GIMP or Photoshop. Use the image tone-mapped with Drago for the first layer and put the Fattal tone-mapped image as the second layer. Set the Layer mode to Overlay and adjust the Opacity such that it looks good. Or you can go the other way round and use the Fattal image for the first layer with the Drago image as the second in Overlay mode and set the Opacity to around 50%.
There is yet another way to get nice HDR photos - by combining Fattal and Mantiuk techniques instead of Fattal and Drago. When using the Mantiuk option, you should adjust the pre-gamma slider to around 0.5 for a slightly lighter image and increase the saturation slider to around 1.0. The tone-mapping process remains the same as before. You can open Fattal image as the first layer and Mantiuk as the second with Layer mode set to Soft light and Opacity adjusted to give a good look. For a dramatic looking (but seemingly artificial) output, you can apply a slight blur mask to the top layer.
9. Open both the tone-mapped images in GIMP or Photoshop. Use the image tone-mapped with Drago for the first layer and put the Fattal tone-mapped image as the second layer. Set the Layer mode to Overlay and adjust the Opacity such that it looks good. Or you can go the other way round and use the Fattal image for the first layer with the Drago image as the second in Overlay mode and set the Opacity to around 50%.
There is yet another way to get nice HDR photos - by combining Fattal and Mantiuk techniques instead of Fattal and Drago. When using the Mantiuk option, you should adjust the pre-gamma slider to around 0.5 for a slightly lighter image and increase the saturation slider to around 1.0. The tone-mapping process remains the same as before. You can open Fattal image as the first layer and Mantiuk as the second with Layer mode set to Soft light and Opacity adjusted to give a good look. For a dramatic looking (but seemingly artificial) output, you can apply a slight blur mask to the top layer.
Summary
10. Lastly, you can post-process the final HDR output image in Photoshop or GIMP to give it a more professional look. You can increase the contrast by applying Curves or Levels, adjust the color or white balance, etc. Sometimes you get strange ghosting artifacts in the final HDR photos, which can be fixed using the original image with Layer mask.
Creating an HDR photo (albeit a fake one) from a single JPG or RAW file
For those without a decent digital camera, all is not lost. You can still create a fake HDR out of a single photo. Open the RAW image file in Qtpfsgui using File -> Load HDR and then tone-map the file directly. Though there's little sense, you can try to achieve fake HDR look with single jpg or raw file. You can directly load a raw file in Qtpfsgui via the File->Load HDR and tone-map directly single raw file.
For those without a decent digital camera, all is not lost. You can still create a fake HDR out of a single photo. Open the RAW image file in Qtpfsgui using File -> Load HDR and then tone-map the file directly. Though there's little sense, you can try to achieve fake HDR look with single jpg or raw file. You can directly load a raw file in Qtpfsgui via the File->Load HDR and tone-map directly single raw file.
For creating overexposed image
For creating underexposed image
Another way is to create two different "exposure" versions of the photograph using the Curves function as shown above. Click in the middle of the curves graph and drag it to the bottom to create an underexposed version and save it as underexposed.jpg. Similarly, drag up to create an overexposed version and save it as overexposed.jpg.
We hope that you will start creating your own HDR photographs using our guide. Please use the space below to let us know about your results.
We hope that you will start creating your own HDR photographs using our guide. Please use the space below to let us know about your results.
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