resize an image before writing to png

[will]

Hi,

It is possible to resize this image to 500 wide x 400 pixels? See code below 

package main

import (

    "image"

    "image/color"

    "image/draw"

    "image/png"

    "os"

)

var (

    white color.Color = color.RGBA{255, 255, 255, 255}

    black color.Color = color.RGBA{0, 0, 0, 255}

    blue  color.Color = color.RGBA{0, 0, 255, 255}

    grey  color.Color = color.RGBA{150, 150, 150, 255}

)

// reference => http://golang.org/doc/articles/image_draw.html

func main() {

    m := image.NewRGBA(image.Rect(0, 0, 640, 480)) 

    // fill m in grey

    draw.Draw(m, m.Bounds(), &image.Uniform{grey}, image.ZP, draw.Src)

    // draw a line

    for i := m.Bounds().Min.X; i < m.Bounds().Max.X; i++ {

        m.Set(i, m.Bounds().Max.Y/2, white)

        m.Set(i, m.Bounds().Max.Y/3, black)

        m.Set(i/2, m.Bounds().Max.Y/4, blue)

    }

    w, _ := os.Create("new.png")

    defer w.Close()

    png.Encode(w, m) 

}

[Nigel Tao]

Import "golang.org/x/image/draw" instead of "image/draw" and you can
use the new Scale methods.

----

package main

import (
"image"
"image/color"

"image/png"
"log"
"os"

"golang.org/x/image/draw"

)

var (
white color.Color = color.RGBA{255, 255, 255, 255}
black color.Color = color.RGBA{0, 0, 0, 255}
blue color.Color = color.RGBA{0, 0, 255, 255}
grey color.Color = color.RGBA{150, 150, 150, 255}
)

// reference => http://golang.org/doc/articles/image_draw.html
func main() {

old := image.NewRGBA(image.Rect(0, 0, 640, 480))
b := old.Bounds()

// fill old in grey
draw.Draw(old, b, &image.Uniform{grey}, image.ZP, draw.Src)

// draw a line
for i := b.Min.X; i < b.Max.X; i++ {
old.Set(i, b.Max.Y/2, white)
old.Set(i, b.Max.Y/3, black)
old.Set(i/2, b.Max.Y/4, blue)
}

new := image.NewRGBA(image.Rect(0, 0, 500, 400))
draw.BiLinear.Scale(new, new.Bounds(), old, old.Bounds(), nil)

w, err := os.Create("new.png")
if err != nil {
log.Fatal(err)
}
defer w.Close()
err = png.Encode(w, new)
if err != nil {
log.Fatal(err)
}
}
----

[will]

I get the following:

cannot find package "golang.org/x/image/draw" in any of:

/usr/local/go/src/golang.org/x/image/draw (from $GOROOT)

[Nigel Tao]

Run:
go get golang.org/x/image/draw
to get that package. (It's not part of the standard library).

[will]

Thanks nigel. it worked. Just wondering, why is it not part of the standard library?  

Several observations:

• I once tried to use "code.google.com/p/draw2d/draw2d", it took a while to go get, which meant the package was big with a lot of dependancies.
• I tried to draw text using functions(as there is no way of drawing text using the standard libraries) . i really wished it was easy to draw text from golang standard libraries.
• I tried drawing wave functions using the standard library, somehow, it just doesnt work, there is no smoothen curve option (wished there was one), so as part of the solution i had to cast to float, divide by 1000 then cast back to int and even then the graph  was messy(with gaps in between). I wished the standard library used float instead of int for m.Set 
• i noticed the y axis increases vertically down in m.Set, is it not possible to increase it vertically up?  mathlab and all graphs increase y vertically up

var x2 int =0

var y2 int =0

        for xn <= int(float64(xz)-float64(length)*0.6) {

            fx = math.Pow(xf, 1)

            xn = x2 + int(fx)

            //fy = math.Cos(math.Pi / (10 - float64(x)))

            fy = math.Pow(float64(fx), 0.3)

            //fy = 5 * math.Pow(float64(fx), 0.5)

            yn = y2 - int(fy)

            x = x + 1

            xf = xf + float64(x)/1000

            m.Set(xn, yn, Green)

        }

I am giving all these observations as i love go and i think the drawing library needs a lot of reworking.

[Dan Kortschak]

Have you had a look at github.com/gonum/plot for these things?

--
You received this message because you are subscribed to the Google Groups "golang-nuts" group.
To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[will]

Thanks kortschak, i will look at the package

[Nigel Tao]

On Wed, Mar 18, 2015 at 5:29 PM, will <wma...@gmail.com> wrote:
> Thanks nigel. it worked. Just wondering, why is it not part of the standard
> library?

It's not part of the standard library because its API might still
change, with more experience, and the standard library's API is
frozen.

> I tried to draw text using functions(as there is no way of drawing text
> using the standard libraries) . i really wished it was easy to draw text
> from golang standard libraries.

The code.google.com/p/freetype-go/freetype library might help you
here. Again, "go get code.google.com/p/freetype-go/freetype".

> I tried drawing wave functions using the standard library, somehow, it just
> doesnt work, there is no smoothen curve option (wished there was one), so as
> part of the solution i had to cast to float, divide by 1000 then cast back
> to int and even then the graph was messy(with gaps in between). I wished
> the standard library used float instead of int for m.Set
> i noticed the y axis increases vertically down in m.Set, is it not possible
> to increase it vertically up? mathlab and all graphs increase y vertically
> up

The Y axis traditionally points up in math, but traditionally points
down in computer graphics. The pixel grid is quantized to integers;
you can't set a fractional pixel. Computer graphics is influenced by
math but isn't math.

As Dan suggested, a plotting package might be more appropriate for your work.