JPEG Functions

Overview

Provides JPEG encoding/decoding capabilities and utilities for image format conversion, masking, and border manipulation. Built on top of TurboJPEG for high-performance compression.

Types

Image

Represents an 8-bit unsigned char image.

typedef struct {
    unsigned char *data;
    int width;
    int height;
    int channels;
} Image;

data

unsigned char*

Pixel data buffer (row-major order)

width

int

Image width in pixels

height

int

Image height in pixels

channels

int

Number of color channels (1 for grayscale, 3 for RGB)

ImageF

Represents a floating-point image.

typedef struct {
    float *data;
    int width;
    int height;
    int channels;
} ImageF;

data

float*

Floating-point pixel data buffer

width

int

Image width in pixels

height

int

Image height in pixels

channels

int

Number of color channels

ImageS

Represents a short integer image.

typedef struct {
    short *data;
    int width;
    int height;
    int channels;
} ImageS;

data

short*

Short integer pixel data buffer

width

int

Image width in pixels

height

int

Image height in pixels

channels

int

Number of color channels

BorderType

Enumeration for border handling modes.

typedef enum {
    BORDER_CONSTANT,
    BORDER_REFLECT
} BorderType;

BORDER_CONSTANT

enum

Fill border with constant value (typically 0)

BORDER_REFLECT

enum

Reflect image pixels at boundaries

Constants

#define RGB_CHANNELS 3
#define GRAY_CHANNELS 1

Functions

decompress_jpeg

Decompresses a JPEG file into an Image structure.

Image decompress_jpeg(const char *filename);

filename

const char*

required

Path to JPEG file to decompress

return

Image

Decompressed image with allocated data buffer

Returns an RGB image (3 channels) regardless of source format. Check img.data != NULL to verify successful loading.

Example

Image img = decompress_jpeg("photo.jpg");
if (img.data != NULL) {
    printf("Loaded %dx%d JPEG\n", img.width, img.height);
    // Process image...
    destroy_image(&img);
} else {
    fprintf(stderr, "Failed to load JPEG\n");
}

compress_jpeg

Compresses an RGB image to JPEG format.

int compress_jpeg(const char *outputFilename, const Image *img, int quality);

outputFilename

const char*

required

Output JPEG file path

img

const Image*

required

Pointer to RGB image to compress (must have 3 channels)

quality

int

required

JPEG quality (1-100, where 100 is best quality)

return

int

1 on success, 0 on failure

The image must have exactly 3 channels (RGB). For grayscale images, use compress_grayscale_jpeg instead.

Example

Image img = create_image("input.jpg");
if (compress_jpeg("output.jpg", &img, 95)) {
    printf("Saved with quality 95\n");
}

compress_grayscale_jpeg

Compresses a grayscale image to JPEG format.

int compress_grayscale_jpeg(const char *outputFilename, const Image *img, int quality);

outputFilename

const char*

required

Output JPEG file path

img

const Image*

required

Pointer to grayscale image (must have 1 channel)

quality

int

required

JPEG quality (1-100)

return

int

1 on success, 0 on failure

Example

Image gray = convert_RGB_to_gray(&img);
compress_grayscale_jpeg("gray.jpg", &gray, 90);
destroy_image(&gray);

convert_RGB_to_gray

Converts an RGB image to grayscale.

Image convert_RGB_to_gray(const Image *img);

img

const Image*

required

Pointer to source RGB image (3 channels)

return

Image

Newly allocated grayscale image (1 channel)

Uses standard luminance conversion: Y = 0.299R + 0.587G + 0.114B

Example

Image rgb = decompress_jpeg("color.jpg");
Image gray = convert_RGB_to_gray(&rgb);
printf("Converted to %d channel(s)\n", gray.channels); // prints 1

create_mask

Creates a horizontal gradient mask for image blending.

Image create_mask(int width, int height, float range, int left, int right);

width

int

required

Mask width in pixels

height

int

required

Mask height in pixels

range

float

required

Gradient transition range as fraction of width (0.0-1.0)

left

int

required

Value for left edge (0 or 1, scaled to 0 or 255)

right

int

required

Value for right edge (0 or 1, scaled to 0 or 255)

return

Image

Grayscale mask image with smooth horizontal gradient

The range parameter controls the transition zone width. For example, 0.1 creates a gradient over 10% of the image width.

Example

// White on left fading to black on right over 20% of width
Image mask = create_mask(1024, 768, 0.2f, 1, 0);

create_vertical_mask

Creates a vertical gradient mask for image blending.

Image create_vertical_mask(int width, int height, float range, int top, int bottom);

width

int

required

Mask width in pixels

height

int

required

Mask height in pixels

range

float

required

Gradient transition range as fraction of height (0.0-1.0)

top

int

required

Value for top edge (0 or 1)

bottom

int

required

Value for bottom edge (0 or 1)

return

Image

Grayscale mask image with smooth vertical gradient

Example

// Black on top fading to white on bottom
Image vmask = create_vertical_mask(1024, 768, 0.15f, 0, 1);

add_border_to_image

Adds border padding to an image.

void add_border_to_image(Image *img,
                         int borderTop, int borderBottom, 
                         int borderLeft, int borderRight,
                         int channels, BorderType borderType);

img

Image*

required

Pointer to image (modified in-place)

borderTop

int

required

Pixels to add on top

borderBottom

int

required

Pixels to add on bottom

borderLeft

int

required

Pixels to add on left

borderRight

int

required

Pixels to add on right

channels

int

required

Number of channels in the image

borderType

BorderType

required

Border fill method (BORDER_CONSTANT or BORDER_REFLECT)

Modifies the image structure in-place by reallocating the data buffer with expanded dimensions.

Example

Image img = decompress_jpeg("photo.jpg");
// Add 10-pixel reflective border on all sides
add_border_to_image(&img, 10, 10, 10, 10, img.channels, BORDER_REFLECT);
printf("New size: %dx%d\n", img.width, img.height);

convert_image_to_image_f

Converts unsigned char image to floating-point format.

void convert_image_to_image_f(Image* in, ImageF *out);

Image*

required

Source image (unsigned char)

out

ImageF*

required

Destination image (must be pre-allocated with same dimensions)

The out image must already be allocated with matching dimensions. Values are converted from [0, 255] to [0.0, 255.0].

Example

Image img = decompress_jpeg("photo.jpg");
ImageF imgf = create_empty_image_f(img.width, img.height, img.channels);
convert_image_to_image_f(&img, &imgf);

convert_image_to_image_s

Converts unsigned char image to short integer format.

void convert_image_to_image_s(Image* in, ImageS *out);

Image*

required

Source image (unsigned char)

out

ImageS*

required

Destination image (must be pre-allocated)

convert_imagef_to_image

Converts floating-point image to unsigned char format.

void convert_imagef_to_image(ImageF* in, Image *out);

ImageF*

required

Source float image

out

Image*

required

Destination image (must be pre-allocated)

Values are clamped to [0, 255] range during conversion.

convert_images_to_image

Converts short integer image to unsigned char format.

void convert_images_to_image(ImageS* in, Image *out);

ImageS*

required

Source short image

out

Image*

required

Destination image (must be pre-allocated)

crop_image_buf

Crops an image buffer by removing borders.

void crop_image_buf(Image *img, int cut_top, int cut_bottom, 
                    int cut_left, int cut_right, int channels);

img

Image*

required

Pointer to image to crop (modified in-place)

cut_top

int

required

Pixels to remove from top

cut_bottom

int

required

Pixels to remove from bottom

cut_left

int

required

Pixels to remove from left

cut_right

int

required

Pixels to remove from right

channels

int

required

Number of channels

Complete Usage Example

#include "jpeg.h"
#include "image_operations.h"

void process_jpeg() {
    // Load JPEG
    Image img = decompress_jpeg("input.jpg");
    if (img.data == NULL) {
        fprintf(stderr, "Failed to load image\n");
        return;
    }
    
    // Convert to grayscale
    Image gray = convert_RGB_to_gray(&img);
    
    // Add reflective border
    add_border_to_image(&gray, 20, 20, 20, 20, 
                        gray.channels, BORDER_REFLECT);
    
    // Convert to float for processing
    ImageF grayf = create_empty_image_f(gray.width, gray.height, 
                                        gray.channels);
    convert_image_to_image_f(&gray, &grayf);
    
    // Process float image...
    // ...
    
    // Convert back to unsigned char
    Image result = create_empty_image(grayf.width, grayf.height, 
                                      grayf.channels);
    convert_imagef_to_image(&grayf, &result);
    
    // Save result
    compress_grayscale_jpeg("output.jpg", &result, 95);
    
    // Cleanup
    destroy_image(&img);
    destroy_image(&gray);
    destroy_image_f(&grayf);
    destroy_image(&result);
}

Getting Started

Core Concepts

API Reference

Examples

Advanced

Overview

Types

Image

ImageF

ImageS

BorderType

Constants

Functions

decompress_jpeg

Example

compress_jpeg

Example

compress_grayscale_jpeg

Example

convert_RGB_to_gray

Example

create_mask

Example

create_vertical_mask

Example

add_border_to_image

Example

convert_image_to_image_f

Example

convert_image_to_image_s

convert_imagef_to_image

convert_images_to_image

crop_image_buf

Complete Usage Example

Build docs developers (and LLMs) love

Getting Started

Core Concepts

API Reference

Examples

Advanced

​Overview

​Types

​Image

​ImageF

​ImageS

​BorderType

​Constants

​Functions

​decompress_jpeg

​Example

​compress_jpeg

​Example

​compress_grayscale_jpeg

​Example

​convert_RGB_to_gray

​Example

​create_mask

​Example

​create_vertical_mask

​Example

​add_border_to_image

​Example

​convert_image_to_image_f

​Example

​convert_image_to_image_s

​convert_imagef_to_image

​convert_images_to_image

​crop_image_buf

​Complete Usage Example

Build docs developers (and LLMs) love

Overview

Types

Image

ImageF

ImageS

BorderType

Constants

Functions

decompress_jpeg

Example

compress_jpeg

Example

compress_grayscale_jpeg

Example

convert_RGB_to_gray

Example

create_mask

Example

create_vertical_mask

Example

add_border_to_image

Example

convert_image_to_image_f

Example

convert_image_to_image_s

convert_imagef_to_image

convert_images_to_image

crop_image_buf

Complete Usage Example