PPI, LPI and DPI - Digital Halftoning

PPI – Pixel per Inch – Image True Resolution

(Display monitor default – 72ppi)

LPI – Lines per Inch (No of Halftone Cells per inch) – Printing

Newsprint- 85-110 lpi;

Consumer Magazine-133-150 lpi;

Fine Quality Art Book- 150-220lpi;

DPI – Dots Per Inch – Printer Dot Density (Typical 600 dpi)

* In Photoshop, Pixels/Inches actually specify LPI of the output to be printed.

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Image RGB to CMYK : Image Conversion - MATLAB Code (RGB to CMYK, CMYK to RGB)

MATAB use makecform and applycform functions to perform this color model conversion Ref: makecform: https://www.mathworks.com/help/images/ref/makecform.html Ref: applycform: https://www.mathworks.com/help/images/ref/applycform.html RGB to CMYK: I_rgb = imread('lena_color.jpg'); %Read the color image C = makecform('srgb2cmyk'); %srgb (standard rgb) to cmyk I_CMYK= applycform(I_rgb,C); TO SAVE IN CMYK Format imwrite(I_CMYK, 'test.tiff'); USE IMFINFO to confirm the conversion imfinfo('test.tiff') the command gives the output ... Width: 512 Height: 512 BitDepth: 32 ColorType: 'CMYK' ... CMYK to RGB: I_CMYK = imread('lena_color.jpg'); %Read the color image C = makecform('cmyk2srgb'); %srgb (standard rgb) to cmyk I_rgb= applycform(I_CMYK, C);

Digital Half Toning - Ordered Dithering - MATLAB Code Bayer/ Ulichney

Digital Half-toning is a technique to convert the gray scale / color image (in the range 0-255) to binary images (in the range 0-1) that is useful for printing (especially black and white printers). Though at first glance dots are clearly visible, as Human Vision System is a low pass filter, when dots are printed closely and viewed from the specific distance it can be perceived as a continuous tone image (i.e. gray scale). In general, half toning techniques is widely used in newspapers, journals and magazines printing. Halftoning algorithms aims for better #Image Quality #Low Complexity #Optimal ink usage Coming to the topic, Ordered dithering is one of the standard technique to produce halftone image from continuous (gray scale) images. Let us assume, the first block containing 'B' is an image matrix and the 'H' is the threshold matrix. And the process is simply a element wise (pixel wise) comparison; if element of B > H (g...

Direct Binary Search Halftoning (DBS) - MATLAB Code (Efficient Direct Binary Search, Halftoning)

Direct binary approach is a heuristic optimization method and is proven to be very powerful to obtain optimized binary patterns. The approach achieves the least minimum square error between the perceived halftone and original image, though swap and toggle operation. The swap operation consists of switching the current pixel with eight of its neighborhood pixels. Toggle operation is about switching the values between 0 to 1 or vice versa (as shown in Fig. below) With each iteration, the perceived error starts to reduce and in finally a superior halftone quality is achieved. The method is computationally very expensive and difficult to implement in hardware. The code for Efficient DBS is provided in the link: (MATLAB Code) https://github.com/SankarSrin/EDBS-Halftoning

Image Processing (Digital Halftoning, Compression, ML & DL Models)

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