Generate HDL and HLS Code from a Contrast Adjustment Algorithm

R2026b

This example shows how to generate HDL and HLS code from a MATLAB^® function that adjusts image contrast by linearly scaling pixel values between upper and lower limits.

In image processing systems, contrast adjustment improves the visibility of features by remapping pixel intensities to fill the available dynamic range. The algorithm builds a histogram of the input frame and determines lower and upper population limits while ignoring outlier pixels. It then applies a gain and offset to scale the remaining pixel values to the desired output range. A temporal damping factor smooths the gain between frames to prevent flickering.

Examine the MATLAB Design and Test Bench

Set up the MATLAB function and test bench for this example. In the MATLAB Command Window, enter:

mlhdlc_demo_setup("mlhdlc_image_scale");

This command opens a temporary working folder with the files required to run this example. The folder includes these files:

• MATLAB function

• Test bench

• <model>_runme.m script, which includes the commands to generate HDL code

• <model>_runme_hls.m script, which includes the commands to generate HLS code

The MATLAB function, mlhdlc_image_scale, processes one pixel per call. It accepts pixel coordinates, a 14-bit pixel value, and parameters that control the scaling behavior. The function outputs remapped pixel coordinates and a scaled 8-bit pixel value.

To view the function, enter:

open mlhdlc_image_scale.m;

The test bench file, mlhdlc_image_scale_tb, verifies the behavior of the MATLAB function. It reads a grayscale test image, streams pixels through the design over two frames, and displays the original and scaled images alongside their histograms. To view the test bench, enter:

open mlhdlc_image_scale_tb.m;

Simulate the Design

To check for run-time errors, simulate the design by running the test bench. In the MATLAB Command Window, enter:

mlhdlc_image_scale_tb

frame: 1
frame: 2

Generate HDL Code

The mlhdlc_image_scale_runme script specifies the target files, enables the settings required for this example, and generates HDL code.

The script specifies the MATLAB function and test bench, then creates a fixed-point configuration object and an HDL configuration object by using the coder.config function. It associates the test bench with both configuration objects.

designName = "mlhdlc_image_scale";
designTB = "mlhdlc_image_scale_tb";
fixptCfg = coder.config("fixpt");
fixptCfg.TestBenchName = designTB;
cfg = coder.config("hdl");
cfg.TestBenchName = designTB;

The script generates code:

codegen("-float2fixed", "fixptCfg", "-config", "cfg", designName, ...
"-launchreport");

Run the Script

Modify the mlhdlc_image_scale_runme script. The script disables synthesis by default. Set the SynthesizeGeneratedCode property to true:

cfg.SynthesizeGeneratedCode = true;

Update the settings for your synthesis tool:

cfg.SynthesisTool = "Xilinx Vivado";
cfg.SynthesisToolChipFamily = "Artix7";
cfg.SynthesisToolDeviceName = "xa7a100t";
cfg.SynthesisToolPackageName = "csg324";
cfg.SynthesisToolSpeedValue = "-1I";

Generate code by running the script:

mlhdlc_image_scale_runme

After code generation completes, the report opens. Examine the generated HDL code in the report.

Generate HLS Code

The mlhdlc_image_scale_runme_hls script specifies the target files, enables the settings required for this example, and generates HLS code.

The script specifies the MATLAB function and test bench, then creates a fixed-point configuration object and an HLS configuration object by using the coder.config function. It associates the test bench with both configuration objects.

designName = "mlhdlc_image_scale";
designTB = "mlhdlc_image_scale_tb";
fixptCfg = coder.config("fixpt");
fixptCfg.TestBenchName = designTB;

The script creates an HLS configuration object by using the coder.config function, associates the test bench, and enables simulation.

cfg = coder.config("hls");
cfg.TestBenchName = designTB;
cfg.GenerateHLSTestBench = true;
cfg.SimulateGeneratedCode = true;

The script generates code:

codegen("-float2fixed", "fixptCfg", "-config", "cfg", designName, ...
"-launchreport");

Run the Script

Modify the mlhdlc_image_scale_runme_hls script. The script disables synthesis by default. Set the SynthesizeGeneratedCode property to true:

cfg.SynthesizeGeneratedCode = true;

Depending on your synthesis tool, set one of these flags to true:

isCodingForStratusHLS = false;
isCodingForVitisHLS = true;

Depending on your synthesis tool, update these settings:

if isCodingForStratusHLS
    cfg.SynthesisTool = "Cadence Stratus HLS";
elseif isCodingForVitisHLS
    cfg.SynthesisTool = "Xilinx Vitis HLS";
    cfg.SynthesisToolChipFamily = "Artix7";
    cfg.SynthesisToolDeviceName = "xa7a100t";
    cfg.SynthesisToolPackageName = "csg324";
    cfg.SynthesisToolSpeedValue = "-1I";
end

Generate code by running the script:

mlhdlc_image_scale_runme_hls

After code generation completes, the report opens. Examine the generated HLS code in the report.