Cross Fading Part 3Merging Images into one Pseudo HDR

GIMP doesn't offer any features for merging HDR images. However, I would like to show you a method to reach similar results. Actually, it is used to cross-fade parts of images, letting you merge images, but you can also merge bracketed photos with this method. In addition, you can create the basis for a pseudo HDR image by editing one preferably underexposed image with the tonality corrections in three different variations, saving each variant as a new image.

The Procedure

In the SampleImages folder on the DVD you will find a subfolder named Exposure Bracketing. Included you will find the RAW files DSCN0832.NEF, DSCN0833.NEF, and DSCN0834.NEF. For this example, I have developed these RAW images as median.png, details-shadows.png, and details- highlights.png, which are also included in the subfolder. The first image was taken with normal exposure settings and serves as the reference image. The second image is overexposed. This is required so that darker parts of the image appear lighter. The last image is underexposed, but it shows the most details in the brighter parts of the picture.

3.15 GIMP AND HDR

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If you like to do the RAW development yourself, the goal of the first step is to open, develop, and save the RAW images, one after another, with either UFRaw or RawPhoto. During the developing, each image should be prepared so that its brightness is optimized. Remember when editing that you have to keep the intended result in mind. You can define the brightness and color combination according to your taste. In the first image, the brightness should be optimized in the median areas (temple); in the second image, in the dark areas (foreground), and in the third image, in the bright areas (sky). After developing the images, you should save them as median.png, details-shadows.png, and details-highlights.png in a folder on your computer. Select a color depth of 8 bits/channel when saving. The steps for this exercise were essentially described in section 2.2 Hence, I will refrain from giving you a detailed account of the work steps. I will simply describe how the images are supposed to look after developing.

If you want to skip the RAW development, you'll find the prepared images median.png, details-shadows.png, and details-highlights.png in the same subfolder as the RAW files.

Figure 3.111

The developed images with optimized areas of brightness: details shadows, medians, details highlights

Figure 3.111

The developed images with optimized areas of brightness: details shadows, medians, details highlights

The first step to produce the pseudo HDR image is to merge the pictures into one file. First, open the details-shadows.png image. It provides the base for the stack of layers. Next, open the median.png image. As described in section 3.6.5 and section 3.13.2, drag the image from the Layers dialog of median.png and drop it into the open image window of details-shadows.png. Now you have it as a layer in the Layers dialog of this image. Follow the same procedure for details-highlights.png. As a result, you should have three layers for the image details-shadows.png. You can close the other opened images now.

In the next step, you should take care that the layers are aligned in the image window. They shouldn't be askew. As is the case here, the adjustment of the images according to the image contents isn't necessary. The photos are all the same size and have been taken with a tripod, so there shouldn't be anything dislodged. It would be different if the pictures were taken freehand.

CHAPTER 3

USING MASKS AND LAYERS—PAINTING, FILLING, AND COLOR TOOLS

In that case, the image layers would have to be aligned above each other as in the method described in section 3.13.2. The overlying layers would have to be made invisible, and in the other layer, the opacity would have to be reduced to 40% in order to align the undermost layer. After the first two layers are aligned, the opacity of those layers would be raised to 100% again and the procedure should be repeated with the next layer.

Label your layers in the image as details-highlights, median, and details-shadows. All three layers are missing an alpha channel, so add one for each using the context menu (right-click on the layer and choose Add Alpha Channel). Then save your image as ldrcollage.xcf in the XCF file format.

Figure 3.112

The image in XCF file format and the corresponding layers in the dock.

Figure 3.112

The image in XCF file format and the corresponding layers in the dock.

3.15 GIMP AND HDR

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