RAW files and 24/48 bit images
PhotoImpact supports RAW files from popular digital camera formats, and enables parameter settings such as white balance or exposure compensation adjustment before saving to TIFF or UFO files. Additionally, PhotoImpact 11 now supports 48 bit image editing and processing (16 bits per R,G,B channel) which gives more colours and smoother tonal gradations than 24 bit images (8 bits per R,G,B channel). Users wishing to obtain highest possible quality and minimal loss during photo editing should consider using 48bit conversions from RAW files.
To start, open the RAW file (File,Open). The 'Open Camera Raw File' dialog box appears, with a preview of the RAW image shown on the left side. Select the preferred RGB colour type, 24 bit or 48 bit (red highlighted area below), then use the adjustment tools on the right side of the dialog box to optimise the image prior to file conversion.
White Balance can be adjusted to correctly display white and other colours according to different lighting conditions, either as set on camera at the time of image capture, or from other settings if the original white balance was incorrect.
Exposure compensation can be used to adjust underexposure or overexposure in the original image. Additional tuning can be acheived by adjusting brightness and shadow settings, while Saturation settings can be used to increase or decrease colours. The effect of any adjustments can be seen in the preview image on the left side of the dialog box. When everything is satisfactory, click OK to convert the RAW file.
Editing 48 bit Images
48 bit images can only be edited with a subset of PI 11 tools, but these include the more important ones for photo editing, such as Levels, Curves, Colour Adjustment, Unsharp Mask, Crop and Gaussian Blur among others.
Saving 48 bit Images
48 bit images can only be saved as TIFF or UFO files (the latter used for images with 2 or more layer objects), and an image saved as 48 bit TIFF will be approximately twice the megabyte size of a 24 bit image. The file size will be dependent on the size of the original RAW file, but an 8 megapixel camera image can produce a 48 megabyte TIFF file.
Comparison of 24 bit and 48 bit Images
The histograms below show a 24 bit and 48 bit file following conversion from RAW, and minor editing using the Levels tool. The histogram of the 24 bit image displays the 'picket line' effect, indicating some loss of colour from the image, frequently seen after editing tools have been used on a photo, while the 48 bit histogram retains its colour distribution. Whether this difference can be seen by the human eye, either on a monitor or print, is perhaps debatable, but the histograms below do suggest that 48 bit images are probably the best option if maximum quality is required from an image.
24 bit image histogram
48 bit image histogram
Posted by Webmaster at January 28, 2006 09:35 PM
