Digital Image Processing Lecture9: Intensity (Gray-level) Transformation Functions

Digital Image Processing Lecture9: Intensity (Gray-level) Transformation Functions

Digital Image Processing Lecture9: Intensity (Gray-level) Transformation Functions using MATLAB Function imadjust Function imadjust is the basic IPT tool for intensity transformations of gray-scale images. It has the syntax: g = imadjust (f, [low_in high_in], [low_out high_out], gamma) Function imadjust

As illustrated in figure 3.2 (above), this function maps the intensity values in image f to new values in g, such that values between low_in and high_in map to values between low_out and high_out. Values below low_in and above high_in are clipped; that is values below low_in map to low_out, and those above high_in map to high_out.

Function imadjust The input image can be of class uint8, uint16, or double, and the output image has the same class as the input. All inputs to function imadjust, other than f, are specified as values between 0 and 1, regardless of the class of f. If f is of class uint8,

imadjust multiplies the value supplied by 255 to determine the actual values to use; if f is of class uint16, the values are multiplied by 65535. Using the empty matrix ([ ]) for [low_in high_in] of for [low_out high_out] results in the default values [0 1].

If high_out is less than low_out, the output intensity is reversed. Function imadjust Parameter gamma specifies the shape of the curve that maps the intensity values of f to create g. If gamma is less than 1, the mapping is weighted toward higher (brighter) output values, as fig 3.2 (a) shows. If gamma is greater than 1, the mapping is weighted toward lower (darker) output values. If it is omitted from the function arguments, gamma defaults to 1 (linear mapping).

Function imadjust Examples Example1: >> f = imread ('baby-BW.jpg'); >> g = imadjust (f, [0 1], [1 0]); >> imshow(f), figure, imshow (g); >> imshow(f), figure, imshow (g);

f g Function imadjust Examples Cont. Example1: This process, which is the digital equivalent of obtaining a

photographic negative, is particularly useful for enhancing white or gray detail embedded in a large dark region. The negative of an image can be obtained also with IPT function imcomplement: g = imcomplement (f); Function imadjust Examples Example2:

>> g = imadjust (f, [0.5 0.75], [0 1], .5); >> imshow(f), figure, imshow (g); f g Function imadjust Examples

Example3: >> g = imadjust (f, [0.5 0.75], [0.6 1], 0.5); >> imshow(f), figure, imshow (g); f g Function imadjust Examples

Example4: >> g = imadjust (f, [ ], [ ], 2); >> imshow(f), figure, imshow (g); f g Logarithmic Transformations

The shape of logarithmic function curve, is similar to the gamma curve where gamma < 1, where low values set to 0 and high values set to 1 on both scales. The shape of the gamma curve is variable (because of the change of low and high values), while the shape of the log function is fixed.

Logarithmic transformations are implemented using the expression: g = c * log (1 + double (f)) Logarithmic Transformations But this function changes the data class of the image to double, so another sentence to return it back to uint8 should be done: gs = im2uint8 (mat2gray(g));

Use of mat2gray brings the values to the range [0 1] and im2uint8 brings them to the range [0 255] Logarithmic Transformations Example: >> g = log(1 + double(f)); >> gs = im2uint8(mat2gray(g));

>> imshow(f), figure, imshow (g), figure, imshow(gs); f g gs Contrast-Stretching Transformation The function shown in the figure below, as indicated in lecture 8, is called a

contrast-stretching transformation function, because it compresses the input levels lower than m into a narrow range of dark levels in the output image. Similarly, it compresses the values above m into a narrow band of light levels in the output. The result is an image of higher contrast. The limiting case shown below (b), shows the output of a binary image. This function is called Thresholding, as mentioned earlier. Thresholding, is a simple tool that can be used for image segmentation. Contrast-Stretching Transformation The function takes the form of:

Where r represents the intensities of the input image, s the corresponding intensity values in the output image, and E controls the slope of the function. Contrast-Stretching Transformation This equation is implemented in MATLAB for the entire image as Note the use of eps to prevent overflow if f has any 0

values. Contrast-Stretching Transformation Example1: >>g = 1 ./ (1+ (100 ./(double(f) + eps)) .^ 20); >> imshow(f), figure, imshow(g); Contrast-Stretching Transformation Example2:

>> g = 1 ./ (1+ (50 ./(double(f) + eps)) .^ 20); >> imshow(f), figure, imshow(g); Contrast-Stretching Transformation Example3: >> g = 1 ./ (1+ (150 ./(double(f) + eps)) .^ 20); >> imshow(f), figure, imshow(g);

Recently Viewed Presentations

  • The Industrial Revolution - lcps.org

    The Industrial Revolution - lcps.org

    Merchant buys raw fiber Women and children clean, sort, spin Merchant collects yarn, pays, takes it to weaver Men weave Merchant pays and picks up woven cloth takes it to the fuller Fuller shapes and cleans Dyer…dyes Merchant sells finished...
  • Cinematic Techniques SpringBoard Unit 2 Hey everyone! Amy

    Cinematic Techniques SpringBoard Unit 2 Hey everyone! Amy

    Thanks Amy. Now, I don't normally take pen and paper to the movie theatre with me. But when I have to study a film like I would with any other piece of text, like a novel, I really like to...
  • Regulating Global Finance MSOC 2

    Regulating Global Finance MSOC 2

    Regulating Global Finance MSOC 2 Presentation of Research Paper outline Matt Smith Overview of presentation and research paper outline Research question Two fundamental problems caused by today's global financial agriculture Keynesian Policy, International Clearing Union Barriers to implementation, Neo Gramscian...
  • Đường Lối Cách Mạng Của Đảng Cộng Sản Việt Nam

    Đường Lối Cách Mạng Của Đảng Cộng Sản Việt Nam

    DANH SÁCH THÀNH VIÊN NHÓM 5 TRẦN THỊ LAN AN (thuyết trình) TRẦN ĐẶNG DIỄM LÊ (thiết kế slide) TRẦN THỊ THÙY DUNG ( xác định nội dung) NGÔ THI HUỆ ( tìm hình ảnh) LÊ THỊ HOÀNG MI (...
  • Abnormal Psychology: Disorders and Treatment

    Abnormal Psychology: Disorders and Treatment

    Personal Distress . An individual's . self-report. of personal distress. Examples. Depression. Anxiety disorders . Note: In order to diagnose a psychological disorder, only one of the three . major criteria needs to be present…
  • Development of Auditory-Visual Speech Perception in Toddlers ...

    Development of Auditory-Visual Speech Perception in Toddlers ...

    Auditory-visual speech perception in young children: language and age-specific factors ... (Native minus Non-native speech perception N-NN) 18 N [voiced vs. voiceless] + 18 NN [voiced vs. prevoiced] Reading Test WRAT-3 reading subtest: 15 letters + 42 words = 57...
  • Presentation Title in This Space Here

    Presentation Title in This Space Here

    Boud, Keogh, and Walker's model is a little more complicated than those we've already covered. Boud's focus was on the place of emotions in professional practice and in reflection. The model reflects the importance of emotions. ... Amanda Brown ...
  • The Impact of Credit Rating Agencies on Financing for ...

    The Impact of Credit Rating Agencies on Financing for ...

    A PROPOSAL: We need to opt for the least drastic means and legislation is not feasible. Instead, self-help could work through two steps. The formation of a voluntary, non-for-profit organization created by the major institutional investors who purchase debt securities...