Image Editing

Tizen offers various image processing features.

The main features of the ImageUtil API include the following:

Converting

You can change the image color space among the supported formats.
Resizing

You can change the image resolution.
Rotating

You can change the image angle around the X or Y axis.
Cropping

You can crop the outer parts of the image.
Decoding or encoding from a file or memory and encoding to a file or memory

You can decode images and encode them with the following formats:
- Bitmap formats: YUV420, YUV422, RGB888, RGBA8888, BGRA8888, and ARGB8888
- Input image formats for decoding: JPEG, PNG, GIF, BMP, WEBP, HEIF, and JPEG XL
- Output image formats for encoding: JPEG, PNG, GIF, BMP, WEBP, and JPEG XL
Note
You must pay attention to how the image quality depends on the size and compression ratio.

Prerequisites

To enable your application to use the image util functionality, follow these steps:

To find out the color spaces supported on the device, use ImageUtil.GetSupportedColorSpaces:


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foreach (var colorSpace in ImageUtil.GetSupportedColorSpaces(ImageFormat.Jpeg))
{
   ...
}

or

var colorSpace = ImageUtil.GetSupportedColorSpaces(ImageFormat.Jpeg);

The supported color space will be one of the Tizen.Multimedia.ColorSpace enumeration.

To transform image, create ImageTransformer and MediaPacket for image source:


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var imageTransformer = new ImageTransformer();
var packet = MediaPacket.Create(new VideoMediaFormat(MediaFormatVideoMimeType.I420, 640, 480));

Convert image color space

To convert one color space of an image to another, follow these steps:

Create a ColorSpaceTransform instance:


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var colorSpaceTransform = new ColorSpaceTransform(ColorSpace.I420);

or, the color space of target image can be set by ColorSpace property after ColorSpaceTransform is created.


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colorSpaceTransform.ColorSpace = ColorSpace.NV12;

Execute the transformation using TransformAsync() of ImageTransformer class:
```
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var resultMediaPacket = await imageTransformer.TransformAsync(packet, colorSpaceTransform);
```
Note
TransformAsync using ColorSpaceTransform only converts the color space. These functions do not change the image width, height, or any other image property. Due to these restrictions of the image processing library, not all color space combinations are supported for conversion.

Resize image

To resize an image, follow these steps:

Create a ResizeTransform instance:


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var resizeTransform = new ResizeTransform(new Size(320, 240));

or, the size of target image can be set by Size property after ResizeTransform is created.


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resizeTransform.Size = new Size(1280, 730);

Execute the transformation using TransformAsync() of ImageTransformer class:


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var resultMediaPacket = await imageTransformer.TransformAsync(packet, resizeTransform);

Note
The image format has no effect on the transformation. If the color space is YUV, then the width and height of the target image must be multiples of eight. This restriction does not apply to the RGB images.

Rotate image

To rotate an image, follow these steps:

Create a RotateTransform instance:


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var rotateTransform = new RotateTransform(Rotation.Rotate90);

or, the rotation of target image can be set by Rotation property after RotateTransform is created.


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rotateTransform.Rotation = Rotation.Rotate180;

Execute the transformation using TransformAsync() of ImageTransformer class:


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var resultMediaPacket = await imageTransformer.TransformAsync(packet, rotateTransform);

Note
The image format has no effect on the transformation. If the color space is YUV, then the width and height of the target image must be multiples of eight. This restriction does not apply to the RGB images.

Crop image

To crop an image, follow these steps:

Create a CropTransform instance:


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var cropTransform = new CropTransform(new Rectangle(0, 0, 100, 100));

or, the area to be cropped can be set by Location or Size property after CropTransform is created.


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cropTransform.Location = new Point(10, 10);
cropTransform.Size = new Size(200, 200);

Execute the transformation using TransformAsync() of ImageTransformer class:


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var resultMediaPacket = await imageTransformer.TransformAsync(packet, cropTransform);

Note
As there is a YUV restriction and the crop start position can be set arbitrarily, the cropped image width and height must be even.

Decode from a file or memory

To decode a JPEG, PNG, GIF, BMP, WEBP, HEIF, or JPEG XL image, follow these steps:

Create a decoder instance as image format:


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var bmpDecoder = new BmpDecoder();


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var pngDecoder = new PngDecoder();


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var jpegDecoder = new JpegDecoder();


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var gifDecoder = new GifDecoder();


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var webPDecoder = new WebPDecoder();


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var heifDecoder = new HeifDecoder();


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var jpegXlDecoder = new JpegXlDecoder();


                
                
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Additionally, you can set the color space and JPEG downscale using SetColorSpace() method and Downscale property:
```
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jpegDecoder.SetColorSpace(ColorSpace.NV12);
jpegDecoder.Downscale = JpegDownscale.OneHalf;
```
Note
Due to the decoder limitations, the color space setting is only supported for decoding the JPEG, the WEBP, the HEIF, and the JPEG XL images. The default color space is ColorSpace.Rgba8888. PNG, GIF, and BMP images are decoded with ColorSpace.Rgba8888.

Execute the decoding using DecodeAsync():


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var result = await jpegDecoder.DecodeAsync("input_file_path");


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var sourceImage = new byte[100];
// set source image to sourceImage buffer
var result = await jpegDecoder.DecodeAsync(sourceImage);

Encode to a file or memory

To encode a raw image, follow these steps:

Create an encoder instance as target image format:


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var bmpEncoder = new BmpEncoder();


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var pngEncoder = new PngEncoder();
var pngEncoder = new PngEncoder(PngCompression.Level1);


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var jpegEncoder = new JpegEncoder();
var jpegEncoder = new JpegEncoder(95);


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var gifEncoder = new GifEncoder();


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var webPEncoder = new WebPEncoder();
var webPEncoder = new WebPEncoder(true);


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var jpegXlEncoder = new JpegXlEncoder();
var jpegXlEncoder = new JpegXlEncoder(true);

Additionally, you can set the JPEG quality or PNG compression using Quality or Compression property:


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jpegEncoder.Quality = 90;


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pngEncoder.Compression = PngCompression.Level3;

Note
The compression is only supported for the PNG images. The default JPEG quality is 75. The default PNG compression is PngCompression.Level6.

Execute the encoding using EncodeAsync():


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var inputImage = new byte[100];
// set source image to encode

using (FileStream outStream = File.Create("output_path"))
{
   await jpegEncoder.EncodeAsync(inputImage, outStream);
}

Note
Due to the encoder limitations, the color space setting is only supported for encoding the JPEG, the WEBP, and the JPEG XL images. The default color space is ColorSpace.Rgba8888. PNG, GIF, and BMP images are encoded with ColorSpace.Rgba8888.

Supported color space formats

The following tables define the supported color space formats.

Table: RGB pixel formats

You can scroll this table.

Label	FOURCC in hex	Bits per pixel	Description
RGB	0x32424752	1, 4, 8, 16, 24, 32	Alias for BI_RGB.
RGBA	0x41424752	16, 32	Raw RGB with alpha. Sample precision and packing is arbitrary and determined using bit masks for each component, as for BI_BITFIELDS.

Table: Packed YUV formats

You can scroll this table.

Label	FOURCC in hex	Bits per pixel	Description
UYVY	0x59565955	16	YUV 4:2:2 (Y sample at every pixel, U and V sampled at every second pixel horizontally on each line). A macropixel contains 2 pixels in 1 u_int32.
YUYV	0x56595559	16	Duplicate of YUY2.

Table: Planar YUV formats

You can scroll this table.

Label	FOURCC in hex	Bits per pixel	Description
YV16	0x36315659	16	8-bit Y plane followed by 8-bit 2x1 subsampled V and U planes.
YV12	0x32315659	12	8-bit Y plane followed by 8-bit 2x2 subsampled V and U planes.
I420	0x30323449	12	8-bit Y plane followed by 8-bit 2x2 subsampled U and V planes.
NV12	0x3231564E	12	8-bit Y plane followed by an interleaved U/V plane with 2x2 subsampling.
NV21	0x3132564E	12	As NV12 with U and V reversed in the interleaved plane.

Quality and size comparison

The following table shows the effect on the image quality and file sizes when using different compression ratios.

Table: Quality and size comparison

You can scroll this table.

Quality	Size (bytes)	Compression ratio	Description
Highest quality (Q = 100)	83,261	2.6:1	Extremely minor artifacts
High quality (Q = 50)	15,138	15:1	Initial signs of subimage artifacts
Medium quality (Q = 25)	9,553	23:1	Stronger artifacts; loss of high-frequency information
Low quality (Q = 10)	4,787	46:1	Severe high frequency loss; artifacts on subimage boundaries (“macroblocking”) are obvious
Lowest quality	-	-	-