Unsigned Longword Integer: A 32-bit unsigned integer ranging from 0 to approximately four billion.Signed Integer: A 16-bit signed integer ranging from -32,768 to +32,767.Unsigned Integer: A 16-bit unsigned integer ranging from 0 to 65535.Pixels in images are commonly represented as byte data. Byte: An 8-bit unsigned integer ranging from 0 to 255.The following types are commonly used for images: The original data type of an image is reflected in IDL when importing the image, but you can convert the type once the image is stored in an IDL variable. Pixel values in an image file can be stored in many different data types. The color dimension always has a size of 3 and is composed of the red, green, and blue color bands (channels) of the image. The other dimension specifies the color of each pixel. RGB Images: Within the three-dimensional array of an RGB image, two of the dimensions specify the location of a pixel within an image.Since indexed images reference color tables composed of up to 256 colors, the data values of these images are usually scaled to range from 0 to 255. Indexed Images: Instead of intensities, a pixel value within an indexed image relates to a color value within a color lookup table.Pixel values usually range from 0 to 255 or are scaled to this range when displayed. Pixels range from least intense (black) to most intense (white). Grayscale Images: Grayscale images represent intensities.This type of image is commonly used as a multiplier to mask regions within another image. The off value is usually 0 and the on value is usually 1. Binary Images: Binary images contain only two values (off or on).Or black and white, where converting to 16-bit before converting to B/W can help avoid banding after edits which wouldn't cause any visible issues in a color file.Various kinds of images can be displayed in IDL.
As your tests have shown, if the original data is in 8bit, the only benefit of converting to 16bit would be for editing (involving significant changes in dynamic range). Supposedly-I haven't tested it-in CS2, 16-bit uses a unsigned 16-bit word rather than signed.Ĭorrect. It's been discussed for years by many of the Adobe folks on various sites, from John Nack, Senior Product Manager of Photoshop to Chris Cox (Photoshop developer since 1996), and various non-Adobe people (Jeff Schewe, Keith Cooper, Andrew Rodney, et al.)Įssentially, in the earlier versions, 16-bit was handled as a signed value-data ranging from -32767 to 32768, only used the positive values (0-32768 ). Where is your comment coming from? (Peter Blaise Monohan) Regarding 15-bits of image and 1-bit of noise - please tell us more in support of your "1-bit of noise" comment. what on opening in a "true" 16-bit program? Spreads out to 16-bit or stays "compressed" and the subsequent program adds a bit of non-image non-information to the image? I'd think, if ever, that the 15-bit image would extrapolate out to 16-bits just like an 8-bit image does, and there are not 8- additional bits of noise in a 16-bit image converted from 8-bits, so why do you think there is one bit of noise in a 15-bit image, especially if it never "lands" in a 16-bit world? Where is your comment coming from? Thanks in advance for a deeper explanation and links or whatever supports your "1-bit of noise" contention.
Real pictures do have smooth gradients as you test with, and they also often have vastly reduced color count often of "only" 50,000 colors in spite of the bit depth being able to carry much more than that. I often use sub-pixel gausian blur when converting from 8-bit to 16-bit to encourage the elimination of "picket fencing" in the histogram and still keep the image smooth yet detailed enough for re-sharpening and to expand the in-between colors and tones to take advantage of the additional bit depth. What screen display bit depth are you looking at the files through? IS it different for each display screen, and THAT is what you are seeing?Īlso, just try opening up the smooth file on the other computer to see if it also displays smooth of not.Īlso, try printing! What a surprise you may get there!
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