Fill one pixel in Golang draw2d package - go

Is there a way to draw an image by filling one pixel at a time in Golang, preferably using the draw2d package?
For example, one can draw a line by using the stroke() command as such (from their getting started page):
package main
impenter code hereort (
"bufio"
"fmt"
"log"
"os"
"code.google.com/p/draw2d/draw2d"
"image"
"image/png"
)
func saveToPngFile(filePath string, m image.Image) {
f, err := os.Create(filePath)
if err != nil {
log.Println(err)
os.Exit(1)
}
defer f.Close()
b := bufio.NewWriter(f)
err = png.Encode(b, m)
if err != nil {
log.Println(err)
os.Exit(1)
}
err = b.Flush()
if err != nil {
log.Println(err)
os.Exit(1)
}
fmt.Printf("Wrote %s OK.\n", filePath)
}
func main() {
i := image.NewRGBA(image.Rect(0, 0, 200, 200))
gc := draw2d.NewGraphicContext(i)
gc.MoveTo(10.0, 10.0)
gc.LineTo(100.0, 10.0)
gc.Stroke()
saveToPngFile("TestPath.png", i)
}
But how could I fill just one pixel, instead of connecting the 2 points? Draw2d is not a necessity, it is simply what I thought would be easiest.

In a vector graphics library like draw2d or Cairo, there is rarely pixel addressing because the model is not a raster of bits. Instead, the vector graphics model has you do things like draw lines in an abstract Euclidean space. This allows device independent drawing and prevents pixel addressing because there are no pixels.
However, draw2d has the standard Package image underlying it, which does allow pixel addressing as with the function Set.
If you are doing many pixels, expect it to be slow. And maybe learn about raster operations.

Related

image.Decode() unknown format

I have an image that is stored in the filesystem. This file should be decoded to an image and then resized. I know how to resize it, but I can't decode the image. Whatever image path/image I insert in program, it results: image: unknown format.
I've already read all sites about this problem, but none of them did help me. This code represents my simplified program logic (I'd like to understand why this error occurs). In advance, thanks for your attention!
import (
"bufio"
"fmt"
"image"
"image/png"
_ "image/jpeg"
_ "image/png"
"log"
"os"
)
func main() {
file, err := os.Open(`D:\photos\img.png`)
if err != nil {
log.Fatal(err)
}
defer file.Close()
config, format, err := image.DecodeConfig(bufio.NewReader(file))
if err != nil {
log.Fatal(err)
}
fmt.Println(format, config.Height, config.Width, config.ColorModel)
decodedImg, format, err := image.Decode(bufio.NewReader(file)) // ERROR HERE
if err != nil {
log.Fatal(err)
}
fmt.Println(format,"decode")
outputFile, err := os.Create(`D:\photos\image.png`)
if err != nil {
log.Fatal(err)
}
defer outputFile.Close()
png.Encode(outputFile, decodedImg)
}
Output:
png 512 512 &{0x4ae340}
2020/07/11 09:37:10 image: unknown format
Both image.Decode and image.DecodeConfig consume the bytes from the passed-in io.Reader.
This means that after DecodeConfig is done, the position in the file is after the bytes already read. image.Decode then comes along with the same underlying file, expects to find the image header, but doesn't.
bufio.NewReader does not reset the position to the beginning of the file (because it can't, it only knows the underlying object is an io.Reader).
You have a few solutions (in order or personal preference):
seek back to the beginning of the file before calling image.Decode. eg: newOffset, err := file.Seek(0, 0)
don't use image.DecodeConfig (this might not be an option)
read the file into a []byte and use a bytes.Buffer
open the file again (not particularly efficient)
As a side note, you don't need to wrap the os.File object in a bufio.Reader, it already implements the io.Reader interface.

Golang: How to convert an image.image to uint16

I am trying to use the go-skeltrack library with some depth images I have (Not using freenect). For that I need to modify the provided example by replacing the kinect images by my own. For that I have to read an image and convert it later to an []uint16 variable. The code which I tried is:
file, err := os.Open("./images/4.png")
if err != nil {
fmt.Println("4.png file not found!")
os.Exit(1)
}
defer file.Close()
fileInfo, _ := file.Stat()
var size int64 = fileInfo.Size()
bytes := make([]byte, size)
// read file into bytes
buffer := bufio.NewReader(file)
_, err = buffer.Read(bytes)
integerImage := binary.BigEndian.Uint16(bytes)
onDepthFrame(integerImage)
Where onDepthFrame is a function which has the form
func onDepthFrame(depth []uint16).
But I am getting the following error while compiling:
./skeltrackOfflineImage.go:155: cannot use integerImage (type uint16) as type []uint16 in argument to onDepthFrame
Which of course refers to the fact that I generated a single integer instead of an array. I am quite confused about the way that Go data types conversion works. Please help!
Thanks in advance for your help.
Luis
binary.BigEndian.Uint16 converts two bytes (in a slice) to a 16-bit value using big endian byte order. If you want to convert bytes to a slice of uint16, you should use binary.Read:
// This reads 10 uint16s from file.
slice := make([]uint16, 10)
err := binary.Read(file, binary.BigEndian, slice)
It sounds like you're looking to get raw pixels. If that's the case, I don't recommend reading the file as binary directly. It means you would need to parse the file format yourself since image files contain more information than just the raw pixel values. There are already tools in the image package to deal with that.
This code should get you on the right track. It reads RGBA values, so it ends up with a 1D array of uint8's of length width * height * 4, since there are four values per pixel.
https://play.golang.org/p/WUgHQ3pRla
import (
"bufio"
"fmt"
"image"
"os"
// for decoding png files
_ "image/png"
)
// RGBA attempts to load an image from file and return the raw RGBA pixel values.
func RGBA(path string) ([]uint8, error) {
file, err := os.Open(path)
if err != nil {
return nil, err
}
img, _, err := image.Decode(bufio.NewReader(file))
if err != nil {
return nil, err
}
switch trueim := img.(type) {
case *image.RGBA:
return trueim.Pix, nil
case *image.NRGBA:
return trueim.Pix, nil
}
return nil, fmt.Errorf("unhandled image format")
}
I'm not entirely sure where the uint16 values you need should come from, but presumably it's data per pixel, so the code should be very similar to this except the switch on trueim should likely check for something other than image.RGBA. Take a look at the other image types in https://golang.org/pkg/image

Convert an image to grayscale in Go

I'm trying to convert an image to grayscale using Go.
I've found the below code, however, I'm struggling to understand it.
It would be extremely helpful if you could explain what each function is doing and where to define the incoming and outgoing file.
package main
import (
"image"
_ "image/jpeg" // Register JPEG format
"image/png" // Register PNG format
"image/color"
"log"
"os"
)
// Converted implements image.Image, so you can
// pretend that it is the converted image.
type Converted struct {
Img image.Image
Mod color.Model
}
// We return the new color model...
func (c *Converted) ColorModel() color.Model{
return c.Mod
}
// ... but the original bounds
func (c *Converted) Bounds() image.Rectangle{
return c.Img.Bounds()
}
// At forwards the call to the original image and
// then asks the color model to convert it.
func (c *Converted) At(x, y int) color.Color{
return c.Mod.Convert(c.Img.At(x,y))
}
func main() {
if len(os.Args) != 3 { log.Fatalln("Needs two arguments")}
infile, err := os.Open(os.Args[1])
if err != nil {
log.Fatalln(err)
}
defer infile.Close()
img, _, err := image.Decode(infile)
if err != nil {
log.Fatalln(err)
}
// Since Converted implements image, this is now a grayscale image
gr := &Converted{img, color.GrayModel}
// Or do something like this to convert it into a black and
// white image.
// bw := []color.Color{color.Black,color.White}
// gr := &Converted{img, color.Palette(bw)}
outfile, err := os.Create(os.Args[2])
if err != nil {
log.Fatalln(err)
}
defer outfile.Close()
png.Encode(outfile,gr)
}
I'm quite new to Go so any suggestions or help would be appreciated.
So as Atomic_alarm pointed out, https://maxhalford.github.io/blog/halftoning-1/ explains how to do this succinctly.
But you're question, if I understand correctly, is about the file opening and creation?
The first step is to use the image package to Decode the opened file into an image.Image struct:
infile, err := os.Open("fullcolor.png")
if err != nil {
return nil, err
}
defer infile.Close()
img, _, err := image.Decode(infile) // img -> image.Image
if err != nil {
return nil, err
}
With this Go image.Image struct, you can convert it to a grayscaled image, image.Gray and then, finally, write or encode the image onto an outgoing file on the disk:
outfile, _ := os.Create("grayscaled.png")
defer outfile.Close()
png.Encode(outfile, grayscaledImage) // grayscaledImage -> image.Gray
Inbetween the infile opening and outfile creating, you have to, of course, convert the image to grayscale. Again, try the link above, and you'll find this function, which takes an image.Image and returns a pointer to a image.Gray:
func rgbaToGray(img image.Image) *image.Gray {
var (
bounds = img.Bounds()
gray = image.NewGray(bounds)
)
for x := 0; x < bounds.Max.X; x++ {
for y := 0; y < bounds.Max.Y; y++ {
var rgba = img.At(x, y)
gray.Set(x, y, rgba)
}
}
return gray
}
Concerning the code you provided (and your comment), you were opening a file with os.Args[1], and creating the file os.Args[2]. os.Args is a slice of arguments passed when running the program, 0 will always be the program itself (main), and whatever follows will with 1, 2, etc. The docs states:
Args hold the command-line arguments, starting with the program name.
var Args []string
so you would run your code above like this:
$ go run main.go infile.png outfile.png
infile.png must to be a file on disk (inside the directory you are running the code from, or the complete path to file).
What I have provide above doesn't use os.Args but rather hard codes the file names into the program.

Golang Converting Image magick object to []byte

I am using the following code which fetch the object from Amazon s3 and after performing resizing and cropping. I want to store it on s3. But the problem is i am not able convert the mw (Image maigck object) to byte array. Which will be used for storing it on s3. Moreover in current method it uses jpeg.Encode. What if the image in .png or .gif format. How will we convert it to []byte?
Could you please also tell me how to evenly crop an image just passing the aspect ratio not cropping coordinates. imgStream.Crop((int)originalWidth, ((int)(originalWidth / masterAspectRatio)), Gravity.Center) like we do it in .net. Reason i am asking is there is no method in library which provides this flexibility.
s3Client := s3.New(session.New(), &aws.Config{Region: aws.String(region)})
params := &s3.GetObjectInput{
Bucket: aws.String(bucketName),
Key: aws.String(keyName),
}
out, err := s3Client.GetObject(params)
if err != nil {
log.Fatal(err)
}
img, err := ioutil.ReadAll(out.Body)
if err != nil {
log.Fatal(err)
}
mw := imagick.NewMagickWand()
err = mw.ReadImageBlob(img)
if err != nil {
log.Fatal(err)
}
//Perform resizing and cropping on mw object
buf := new(bytes.Buffer)
err = jpeg.Encode(buf, mw, nil)
sendmw_s3 := buf.Bytes()
paramsPut := &s3.PutObjectInput{
Bucket: aws.String(masterBucketName),
Key: aws.String(keyName),
Body: bytes.NewReader(sendmw_s3),
}
resp, err := s3Client.PutObject(paramsPut)
if err != nil {
log.Fatal(err)
}
Error :
cannot use mw (type *imagick.MagickWand) as type image.Image in argument to jpeg.Encode:
*imagick.MagickWand does not implement image.Image (missing At method)
You need to use the func (mw *MagickWand) GetImageBlob() []byte function.
It returns a slice of bytes containing a complete encoded image for the current file format (JPEG, gif, PNG...).
The returned data can therefore be saved to disk, or sent to s3 as-is.
See https://gowalker.org/github.com/gographics/imagick/imagick#MagickWand_GetImageBlob for the documentation.
This question is actually two questions, and #SirDarius answered one of them, by suggesting the use of GetImageBlob(). You can also use SetImageFormat() to change the image format before generating the blob.
For the part about the crop, I am sure there are a bunch of ways to do this with ImageMagick. The way I have done it, to achieve a center crop is to first transform the image so that the smaller dimension fits into my desired target resolution. And then to crop away the parts that overflow.
// Create a new image where smallest dimension is fit
// and the rest overflows the dimensions
size := fmt.Sprintf("%dx%d^+0+0", w, h)
tx := wand.TransformImage("", size)
// Center Crop away the extra parts of the image, to perform
tx.SetImageGravity(imagick.GRAVITY_CENTER)
offsetX := -(int(w) - int(tx.GetImageWidth())) / 2
offsetY := -(int(h) - int(tx.GetImageHeight())) / 2
err := tx.ExtentImage(w, h, offsetX, offsetY)
...

How to split gif into images

How can I split gif into images in go?
image/gif's DecodeAll return GIF, which contains an array of palette. But don't know how to convert each palette into an image?
Consider the following:
Frames can contain transparent pixels or areas, a good example is this image on wikipedia which (I guess) has one of these full-color blocks per frame and the rest of the frame transparent.
This introduces a problem for you: Especially with animated GIFs, that do not use multiple frames to create a true-colored static image, the frames that DecodeAll returns are not what you actually see if you, for example, open the image in your browser.
You'll have to process the image in the same way your browser would, i.e. leave the old frames on a kind of canvas and overpaint with the new frame. BUT this is not always true. GIF frames can, AFAIK, contain a disposal method, specifying how (or if?) you should dispose of the frame.
Anyways, to get to your point, the most simple approach that will also work in most cases is something like
import (
"errors"
"fmt"
"image"
"image/draw"
"image/gif"
"image/png"
"io"
"os"
)
// Decode reads and analyzes the given reader as a GIF image
func SplitAnimatedGIF(reader io.Reader) (err error) {
defer func() {
if r := recover(); r != nil {
err = fmt.Errorf("Error while decoding: %s", r)
}
}()
gif, err := gif.DecodeAll(reader)
if err != nil {
return err
}
imgWidth, imgHeight := getGifDimensions(gif)
overpaintImage := image.NewRGBA(image.Rect(0, 0, imgWidth, imgHeight))
draw.Draw(overpaintImage, overpaintImage.Bounds(), gif.Image[0], image.ZP, draw.Src)
for i, srcImg := range gif.Image {
draw.Draw(overpaintImage, overpaintImage.Bounds(), srcImg, image.ZP, draw.Over)
// save current frame "stack". This will overwrite an existing file with that name
file, err := os.Create(fmt.Sprintf("%s%d%s", "<some path>", i, ".png"))
if err != nil {
return err
}
err = png.Encode(file, overpaintImage)
if err != nil {
return err
}
file.Close()
}
return nil
}
func getGifDimensions(gif *gif.GIF) (x, y int) {
var lowestX int
var lowestY int
var highestX int
var highestY int
for _, img := range gif.Image {
if img.Rect.Min.X < lowestX {
lowestX = img.Rect.Min.X
}
if img.Rect.Min.Y < lowestY {
lowestY = img.Rect.Min.Y
}
if img.Rect.Max.X > highestX {
highestX = img.Rect.Max.X
}
if img.Rect.Max.Y > highestY {
highestY = img.Rect.Max.Y
}
}
return highestX - lowestX, highestY - lowestY
}
(untested, but should work)
Note that gif.DecodeAll can and will panic frequently, because a lot of the GIF images on the internet are somewhat broken. Your browser tries to decode them and will, for example, replace missing colors with black. image/gif will not do that, but panic instead. That's why we defer the recover.
Also, I used the getGifDimensions for a similar reason as stated above: single frames need not be what you see in your browser. In this case, the frames are just smaller than the complete image, that's why we have to iterate over all frames and get the "true" dimensions of the image.
If you really really want to do it right, you should probably read the GIF spec GIF87a, GIF89a and something like this article which is a lot easier to understand. From that, you should decide how to dispose of the frames and what to do with transparency while overpainting.
EDIT: Some of the effects mentioned earlier can be observed easily if you split some GIFs online, for example this or this - play around with "Ignore optimizations" and "Redraw every frame with details from previous frames" to see what I mean.
image.Image is an interface, and *image.Paletted implements the interface, so for example if you want to save every frame of a GIF into a PNG file, you can just encode every image:
for i, frame := range img.Image {
frameFile, err := os.OpenFile(fmt.Sprintf("%d.png", i+1), os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0666)
if err != nil {
log.Fatal(err)
}
err = png.Encode(frameFile, frame)
if err != nil {
log.Fatal(err)
}
// Not using defer here because we're in a loop, not a function.
frameFile.Close()
}

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