Browse Prior Art Database

Requantization Process for Image Data

IP.com Disclosure Number: IPCOM000062182D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Hehl, W: AUTHOR [+2]

Abstract

Stored image data frequently have to be requantized to suit the requirements of the user of the image processing system. While the two corner points (sh bl) and (hi wh) are retained (see figure), the user is able to explicitly define the shadow and highlight spread, for instance, s shadow spread (between 0 and B), say, s = 2, doubles the shadow resolution h highlight spread (between 0 and B), say, h = 2, doubles the highlight spread. Optionally, the user is free to define the midtone shift as previously mi midtone shift (in the center). Mathematically, these three parameters (and thus a maximum number of 7 parameters) are relatively easy to specify. The new output value y is computed in steps from an input value x: (Image Omitted) In the above case, the midtone shift is undefined.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 96% of the total text.

Page 1 of 2

Requantization Process for Image Data

Stored image data frequently have to be requantized to suit the requirements of the user of the image processing system. While the two corner points (sh bl) and (hi wh) are retained (see figure), the user is able to explicitly define the shadow and highlight spread, for instance, s shadow spread (between 0 and B), say, s = 2, doubles the shadow resolution h highlight spread (between 0 and B), say, h = 2, doubles the highlight spread. Optionally, the user is free to define the midtone shift as previously mi midtone shift (in the center). Mathematically, these three parameters (and thus a maximum number of 7 parameters) are relatively easy to specify. The new output value y is computed in steps from an input value x:

(Image Omitted)

In the above case, the midtone shift is undefined. If it is to be explicitly defined by the user (where mi = 0 is a non-trivial specification), an additional step 3 is required: 3. Correction to a predetermined midtone shift yp E yp + 2 (8 mi'- s' + h') xp2 (1 - xp2), where s', h' and mi' are the transformed values. 4. Retransformation to the original coordinates y = yp $ (wh - bl) + bl. It is pointed out that this algorithm is not used for each pel but only once for each of the (say, 255) scanning values. Subsequently, the possible output values are available in the form of a table, i.e., the requirements of the user have been translated, and quantization of the image data can proceed as previously...