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## High Dynamic Range Imaging

This example shows how to generate HDL code from a MATLAB® design that implements a high dynamic range imaging algorithm.

### Algorithm

High Dynamic Range Imaging (HDRI or HDR) is a set of methods used in imaging and photography to allow a greater dynamic range between the lightest and darkest areas of an image than current standard digital imaging methods or photographic methods. HDR images can represent more accurately the range of intensity levels found in real scenes, from direct sunlight to faint starlight, and is often captured by way of a plurality of differently exposed pictures of the same subject matter.

### MATLAB Design

```design_name = 'mlhdlc_hdr'; testbench_name = 'mlhdlc_hdr_tb'; ```

Let us take a look at the MATLAB design

```dbtype(design_name); ```
```1 function [valid_out, x_out, y_out, ... 2 HDR1, HDR2, HDR3] = mlhdlc_hdr(YShort1, YShort2, YShort3, ... 3 YLong1, YLong2, YLong3, ... 4 plot_y_short_in, plot_y_long_in, ... 5 valid_in, x, y) 6 % 7 8 % Copyright 2013-2015 The MathWorks, Inc. 9 10 % This design implements a high dynamic range imaging algorithm. 11 12 plot_y_short = plot_y_short_in; 13 plot_y_long = plot_y_long_in; 14 15 %% Apply Lum(Y) channels LUTs 16 y_short = plot_y_short(uint8(YShort1)+1); 17 y_long = plot_y_long(uint8(YLong1)+1); 18 19 y_HDR = (y_short+y_long); 20 21 %% Create HDR Chorm channels 22 % HDR per color 23 24 HDR1 = y_HDR * 2^-8; 25 HDR2 = (YShort2+YLong2) * 2^-1; 26 HDR3 = (YShort3+YLong3) * 2^-1; 27 28 %% Pass on valid signal and pixel location 29 30 valid_out = valid_in; 31 x_out = x; 32 y_out = y; 33 34 end ```
```dbtype(testbench_name); ```
```1 2 % 3 4 % Copyright 2013-2015 The MathWorks, Inc. 5 6 % Clean screen and memory 7 close all 8 clear mlhdlc_hdr 9 set(0,'DefaultFigureWindowStyle','docked') 10 11 12 %% Read the two exposed images 13 14 short = imread('mlhdlc_hdr_short.tif'); 15 long = imread('mlhdlc_hdr_long.tif'); 16 17 % define HDR output variable 18 HDR = zeros(size(short)); 19 [height, width, color] = size(HDR); 20 21 figure('Name', [mfilename, '_plot']); 22 subplot(1,3,1); 23 imshow(short, 'InitialMagnification','fit'), title('short'); 24 25 subplot(1,3,2); 26 imshow(long, 'InitialMagnification','fit'), title('long'); 27 28 29 %% Create the Lum(Y) channels LUTs 30 % Pre-process 31 % Luminance short LUT 32 ShortLut.x = [0 16 45 96 255]; 33 ShortLut.y = [0 20 38 58 115]; 34 35 % Luminance long LUT 36 LongLut.x = [ 0 255]; 37 LongLut.y = [ 0 140]; 38 39 % Take the same points to plot the joined Lum LUT 40 plot_x = 0:1:255; 41 plot_y_short = interp1(ShortLut.x,ShortLut.y,plot_x); %LUT short 42 plot_y_long = interp1(LongLut.x,LongLut.y,plot_x); %LUT long 43 44 %subplot(4,1,3); 45 %plot(plot_x, plot_y_short, plot_x, plot_y_long, plot_x, (plot_y_long+plot_y_short)), grid on; 46 47 48 %% Create the HDR Lum channel 49 % The HDR algorithm 50 % read the Y channels 51 52 YIQ_short = rgb2ntsc(short); 53 YIQ_long = rgb2ntsc(long); 54 55 %% Stream image through HDR algorithm 56 57 for x=1:width 58 for y=1:height 59 YShort1 = round(YIQ_short(y,x,1)*255); %input short 60 YLong1 = round(YIQ_long(y,x,1)*255); %input long 61 62 YShort2 = YIQ_short(y,x,2); %input short 63 YLong2 = YIQ_long(y,x,2); %input long 64 65 YShort3 = YIQ_short(y,x,3); %input short 66 YLong3 = YIQ_long(y,x,3); %input long 67 68 valid_in = 1; 69 70 [valid_out, x_out, y_out, HDR1, HDR2, HDR3] = mlhdlc_hdr(YShort1, YShort2, YShort3, YLong1, YLong2, YLong3, plot_y_short, plot_y_long, valid_in, x, y); 71 72 % use x and y to reconstruct image 73 if valid_out == 1 74 HDR(y_out,x_out,1) = HDR1; 75 HDR(y_out,x_out,2) = HDR2; 76 HDR(y_out,x_out,3) = HDR3; 77 end 78 end 79 end 80 81 %% plot HDR 82 HDR_rgb = ntsc2rgb(HDR); 83 subplot(1,3,3); 84 imshow(HDR_rgb, 'InitialMagnification','fit'), title('hdr '); ```

### Simulate the Design

It is always a good practice to simulate the design with the testbench prior to code generation to make sure there are no runtime errors.

```mlhdlc_hdr_tb ```

### Setup for the Example

Executing the following lines copies the necessary files into a temporary folder

```mlhdlc_demo_dir = fullfile(matlabroot, 'toolbox', 'hdlcoder', 'hdlcoderdemos', 'matlabhdlcoderdemos'); mlhdlc_temp_dir = [tempdir 'mlhdlc_hdr']; % create a temporary folder and copy the MATLAB files cd(tempdir); [~, ~, ~] = rmdir(mlhdlc_temp_dir, 's'); mkdir(mlhdlc_temp_dir); cd(mlhdlc_temp_dir); % copy files to the temp dir copyfile(fullfile(mlhdlc_demo_dir, [design_name,'.m*']), mlhdlc_temp_dir); copyfile(fullfile(mlhdlc_demo_dir, [testbench_name,'.m*']), mlhdlc_temp_dir); copyfile(fullfile(mlhdlc_demo_dir, 'mlhdlc_hdr_long.tif'), mlhdlc_temp_dir); copyfile(fullfile(mlhdlc_demo_dir, 'mlhdlc_hdr_short.tif'), mlhdlc_temp_dir); ```

### Create a New HDL Coder™ Project

```coder -hdlcoder -new mlhdlc_hdr_prj ```

Next, add the file 'mlhdlc_hdr.m' to the project as the MATLAB Function and 'mlhdlc_hdr_tb.m' as the MATLAB Test Bench.

You can refer to Getting Started with MATLAB to HDL Workflow tutorial for a more complete tutorial on creating and populating MATLAB HDL Coder projects.

### Creating constant parameter inputs

This example shows to use pass constant parameter inputs.

In this design the input parameters 'plot_y_short_in' and 'plot_y_long_in' are constant input parameters. You can define them accordingly by modifying the input types as 'constant(double(1x256))'

'plot_y_short_in' and 'plot_y_short_in' are LUT inputs. They are constant folded as double inputs to the design. You will not see port declarations for these two input parameters in the generated HDL code.

Note that inside the design 'mlhdlc_hdr.m' these variables are reassigned so that they get properly fixed-point converted. This is not necessary if these are purely used as constants for defining sizes of variables for example and not part of the logic.

### Run Fixed-Point Conversion and HDL Code Generation

Launch HDL Advisor and right click on the 'Code Generation' step and choose the option 'Run to selected task' to run all the steps from the beginning through the HDL code generation.

### Convert the design to fixed-point and generate HDL code

The following script converts the design to fixed-point, and generate HDL code with a test bench.

``` exArgs = {0,0,0,0,0,0,coder.Constant(ones(1,256)),coder.Constant(ones(1,256)),0,0,0}; fc = coder.config('fixpt'); fc.TestBenchName = 'mlhdlc_hdr_tb'; hc = coder.config('hdl'); hc.GenerateHDLTestBench = true; hc.SimulationIterationLimit = 1000; % Limit number of testbench points codegen -float2fixed fc -config hc -args exArgs mlhdlc_hdr```

Examine the generated HDL code by clicking on the hyperlinks in the Code Generation Log window.

### Clean up the Generated Files

You can run the following commands to clean up the temporary project folder.

```mlhdlc_demo_dir = fullfile(matlabroot, 'toolbox', 'hdlcoder', 'hdlcoderdemos', 'matlabhdlcoderdemos'); mlhdlc_temp_dir = [tempdir 'mlhdlc_hdr']; clear mex; cd (mlhdlc_demo_dir); rmdir(mlhdlc_temp_dir, 's'); ```