You are currently browsing the tag archive for the ‘photomatix’ tag.
The digital photographic files of the valves have been worked in post production. I have worked methodically on them and I have now finalised them. Just to recap, the process followed was:
1. I got a bracketed exposure of my referent, minimum of 3 different ev
2. I imported them into Photomatix and created an HDR tonnedmapped image
3. I opened the image in Photoshop and made it Black and White. These changed the tonal values quite a bit, to compensate for this I had to make adjustments that vary slightly on each valve picture. For this particular valve, I choose a blue photo filter (making reds and oranges become a touch darker and blues and greens slightly lighter) and a touch more red with colour balance to enhance the texture on the dark areas. I also corrected the levels of the center bolt as the HDR process had made the white tones on this particular area expand and loose detail. Then to finish the overall correction of tonality I made an adjustment with the Curves, this varies greatly from valve to valve, it just has to be adjusted till you feel happy with the result. Keeping in mind that my monitor is from an Imac and although I use RGB (1998) as a standard profile, my monitor is not properly calibrated, so, what you see on the screen may not look precisely like what comes out of a printer.
After all the adjustments have been made then I create a mask that isolates the valve and allows the different exposure background to be seen. This is a lengthy process but well worthy. Creating this result:
To prepare this images to be printed onto a positive transparency I need to make sure that the resolution is at 360 ppi which provides optimum sharpness, based on the fact that it can be divided evenly into 1440 or 2880 printer driver resolutions. The size of the transparency should be smaller than the size of the plate. If the transparency is larger than the plate, the transparency gets bent over the lip of the plate, causing a dark shadow along the perimeter in some cases.
In order to get a broader range of shadow detail, I compensated with a tonal curve, which is, in fact, required to get the broadest range of shadow detail from the print. Most of the image detail is natively retained using the approach contained herein, however shadow detail will get buried in most images without an adjustment to the curve. A good process compensation curve basically lowers the contrast of the image, adjusting the entry levels for the black of the compensation curve to 94%. Contrast is then naturally reintroduced when it gets transferred to polymer plate. Without it, the image will appear too contrasty – especially in the blacks.
As a final check on the flattened image, I made sure that the histogram represented covered the entire length of the graph, checking with the Threshold tool and finally converted the image to 8 bit.
HDR images are the combination of a series of bracketed exposures into a single image which encompasses the tonal detail of the entire series. HDR enable a greater range of tonal detail.
image by Bettina & Uwe Steinmueller
Capturing identically positioned images and bracketing your exposure by varying the shutter speed (this way the camera can dramaticaly change the amount of light that lets in) will provide you with different tone images which you can use to merge to HDR. At least three different exposures are recommended for optimum accuracy in an even tonal distribution.
Some cameras have a setting called Auto Exposure Bracketing (AEB) it allows you to take 3 or more images with a chosen change of exposure. In order to uses this setting for HDR you need a camera that allows your shoots to be spaced by more than one EV step. Another important factor is the number of frames per second (burst rate) as a slow bus rate will have the disadvantage of anything moving on the image will become blurred and it will produce ghosting as it moves across the 3 images.
Adobe Photoshop will combine all exposures into a single 32-bit HDR file. As it stands, very few image processing functions can be applied to a 32-bit HDR file, so it is of little use other than for archival purposes. The image may still appear quite dark; only once it has been converted into a 16 or 8-bit image (using tonal mapping) will it begin to look more like the desired result.
Using tonal mapping you convert the HDR image into a 16-bit image. There are several tonal mapping methods. When you convert your HDR image to 8bits/channel you will get the options of different methods including Local Adaptation, which is the most flexible method and probably the one which is of most use to photographers. Unlike the other methods, this one changes how much it brightens or darkens regions on a per-pixel basis. This has the effect of tricking the eye into thinking that the image has more contrast, which is often critical in contrast-deprived HDR images. This method also allows changing the tonal curve to better suit the image.
HDR images which have been converted into 8 or 16-bit often require touching up in order to improve their color accuracy. Subtle use of levels and saturation can drastically improve problem areas in the image.
** information via www.cambridgeincolour.com**
Another program that has been recommended to use for creating HDR files is Photomatix Pro is a standalone application offering two methods of tone mapping, six methods of exposure blending, an alignment tool for out-of-register images, 16-bit support, and batch processing. The latest version of Photomatix will detect if your TIFF’s have the same EXIF (Exchangeable Image File Format) info and it will ask you to confirm which images have which exposure settings. This means you don’t have to remove the EXIF from them anymore.
