When HDR-image is received, it must be processed so that it can be displayed on a standard computer monitor or printed. HDR-image is a 32-bit file containing billions levels. At the same time the computer display – 8-bit device, and may submit no more than 256 levels. Therefore, in order to see all the details of the image in one HDR-image, it is necessary to process and convert, bringing to an 8 – or 16-bit LDR-file (Low Dynamic Range) with lower DD. This process is called transformation of the brightness range.
Program create HDR-images, as in Photoshop (CS2 and CS3), and in Photomatix, contain appropriate conversion tools brightness range.
Transformation range of brightness in Photoshop CS2/CS3
In terms of traditional photography creation of HDR-images similar processing of exposed film when the film show – it’s polraboty. The next step is similar to the creation of the negative print, which can be represented and the viewer is to convert HDRI-file in LDR-image in which all parts are visible.
Merge to HDR window
Once Photoshop generate HDR-image, it appears in the Merge to HDR. The strip on the left shows the original image, and their relative exposure window Include / Exclude. If you put a tick in the box, the image will be involved in the formation of HDR-images. If a tick removed, this image will be deleted from the original set that will be immediately visible in the preview window.
experimenting with the original pictures, you can fine-tune the HDR-image to its conversion in LDR-image. Get creative to create an expressive image, and remember that if you have access to the full DD, it does not mean that you should use it. Indistinguishable light and shadow can give an interesting effect shot.
Figure 1. Presented on the screen working screen function Merge to HDR in Photoshop CS2 and CS3.
Right Preview Image window displays bit depth. While the image is converted to LDR-image, this window shows the 32 bits per channel. Under the given bit depth HDR-histogram that shows the full tonal range of HDR-images. Because the monitor can not display the full range of HDR-data displays only part of tonal image indicating the engine on the scale. Adjusting the position of the engine, you can display different parts of the full tonal range. (Regulation engine does not affect the HDR-image stored before conversion of the brightness range.) As a guideline on the chart are red label after 1 DD stage.
Figure 2. HDR-image needs to convert the brightness range and prior to its submission to the devices with low DD. such as a computer monitor. Before converting the brightness range is not visible all the available information, as shown in the HDR-image to Portland Bill lighthouse.
Prior to the conversion of the brightness range, then click OK. Photoshop creates a 32-bit HDR-image and open it. At this point it is important to keep the menu command Save As (File “Save As) from the main menu. This will give you an opportunity to change all your settings and then convert the brightness range, without repeating the process of creating an HDR-image.
The position slider does not affect the state in which the HDR-image is saved to a transformation of the brightness range.
Transformation range of brightness part 2
There are two basic formats HDR-files, which are stored in the image: Radiance RGBE (extension. Hdr) and OpenEXR (extension. Exr). Details of the differences between the HDRI-formats are shown below. To begin, select OpenEXR.
To enable HDR-conversion, select File “Mode” 16 Bits / Channel from the main menu. Dialog box HDR Conversion. Photoshop allows you to apply four different methods of conversion range of brightness that can be selected from the drop down menu at the top of the window Method option. The first three options (Exposure and Gamma, Highlight Compression and Equalize Histogram) provide global settings. They are easy to use, but they are functionally limited. To accurately convert the brightness range is more useful option Local Adaptation.
Above. In Photoshop (CS2 / 3) HDR-conversion starts when the main menu mode is selected in 16 bits / channel, or 8 bits / channel.
There are several formats HDR-files, of which two are most common: Radiance RGBE and OpenEXR. Format Radiance RGBE DD has more (much more than you need for photos), but less accurate. OpenEXR format covers the entire visible range of colors and can store a much greater range than available human vision. These properties make it an ideal format for archiving images. Increased accuracy OpenEXR format is important when applied multiple mixing and other operations in which errors can accumulate.
Local Adaptation and mode conversion of the brightness range
The main role of Local Adaptation mode to convert the brightness range is to reduce the contrast in the image space by a large decrease in local contrast, which allows more accurate modeling of human vision. When applying Mode Local Adaptation, the algorithm converts the value to each pixel based primarily on data of surrounding pixels, rather than pixel by a specific value (as in the case of options Exposure and Gamma, Highlight Compression or Equalize Histogram). Practically, this means not just compression and tension tones, and a complete replacement of the tone relative to the adjacent tones, thus reducing global contrast (large area) without disturbing the local (in a small area).
If you choose to convert the brightness range option Local Adaptation, a dialog box HDR-conversion change. At this stage, click on the Tone Curve and Histogram, to open the histogram graph of the tone curve, which is similar to the tool Curves tool in Photoshop.
The main advantage of the conversion range of brightness using Local Adaptation is that apart along the tone curve control points that facilitate the management and redistribution of the contrast level to which you can compress DD when converting HDR-images in 8 – or 16-bit LDR image.
tonal curve settings are performed in much the same way as in setting Curves adjustments, applied to the LDR-images in Photoshop. Please transfer the endpoint of the tone curve so that the most dark and light pixels correspond to the histogram. Then add a control point on the curve that it has S-shaped, or even a series of S-shaped curves, because you are working with a much larger DD than LDR-image.
Slope around each control point is determined by the desired contrast. It has more slope, the greater the contrast, the smaller slope reduces the contrast, creating an eye-pleasing distribution of tones in an area that is designated checkpoints.
Reduction to LDR-image can be achieved for relatively simple S-curves using the Curves tool in Photoshop. However, due to the large DD HDR-image tone curve to adjust local contrasts are usually more complex.
Options range conversion brightness PHOTOSHOP CS2/CS3
1. Exposure and Gamma – optional settings like Brightness / Contrast, used in image processing with low DD in Photoshop. Exposure controls the brightness setting. Gamma – contrast.
2. Highlight Compression – use a custom tone curve to reduce the contrast in highlights and lightening and restore contrast in the midtones and shadows.
3. Equalize Histogram – use a custom tone curve for smooth distribution histograms contrasting sites in the LDR-image.
Note: Each of these options is used in the process of converting a range of brightness across the image, which may run counter to many photographic subjects. Local Adaptation option can produce transform the individual pixels or local areas.
The transformation of the brightness range in 8-bit mode. / Channel
You can switch process HDR-conversion mode 8 bits / channel from the main menu of the program Photoshop. However, the process of converting the brightness range to perform better in the 16 bit / channel.