B4J Question How to resize and save a captured bitmap without losing quality?

jroriz · May 22, 2025

I'm capturing a small portion of the screen using the following code:

B4X:

Dim Bitmap1 As B4XBitmap = Capture(100, 100, 100, 100)
Bitmap1 = Bitmap1.Resize(Bitmap1.Width*4, Bitmap1.Height*4, True)

Dim Out As OutputStream
Out = File.OpenOutput("C:\MEAPAGUE", "Test.png", False)
Bitmap1.WriteToStream(Out, 100, "PNG")
Out.Close

I need to save the image in a larger size, but without losing quality. When I resize the bitmap, the image becomes pixelated or blurry. Is there a way to upscale the image with better quality or apply some kind of smoothing or interpolation?

Thanks in advance.

TILogistic · May 22, 2025

you can use this library

[Source code] ImageScaler

Introduction: I don't know if there is any library exist to resize image in B4J non-UI app. I thought such library will be useful to process images for web server in building REST API for e-commerce or e-learning web apps. I found an example on web and chose the third method, from an old project...

www.b4x.com

or in b4j javaobject

B4X:

Sub ResizeImage(original As Image, newWidth As Int, newHeight As Int) As Image
    Dim jo As JavaObject
    jo.InitializeStatic("java.awt.image.BufferedImage")
    Dim bufferedImage As JavaObject = jo.CreateNew(newWidth, newHeight, 2) ' 2 = BufferedImage.TYPE_INT_ARGB

    Dim g2d As JavaObject = bufferedImage.RunMethod("createGraphics", Null)
    g2d.RunMethod("setRenderingHint", Array(jo.GetField("KEY_INTERPOLATION"), jo.GetField("VALUE_INTERPOLATION_BICUBIC")))
    g2d.RunMethod("setRenderingHint", Array(jo.GetField("KEY_ANTIALIASING"), jo.GetField("VALUE_ANTIALIAS_ON")))
    g2d.RunMethod("drawImage", Array(original, 0, 0, newWidth, newHeight, Null))
    g2d.RunMethod("dispose", Null)

    Dim resizedImage As Image = bufferedImage
    Return resizedImage
End Sub

jroriz · May 22, 2025

TILogistic said:
you can use this library

[Source code] ImageScaler

Introduction: I don't know if there is any library exist to resize image in B4J non-UI app. I thought such library will be useful to process images for web server in building REST API for e-commerce or e-learning web apps. I found an example on web and chose the third method, from an old project...

www.b4x.com

or in b4j javaobject

B4X:

Sub ResizeImage(original As Image, newWidth As Int, newHeight As Int) As Image Dim jo As JavaObject jo.InitializeStatic("java.awt.image.BufferedImage") Dim bufferedImage As JavaObject = jo.CreateNew(newWidth, newHeight, 2) ' 2 = BufferedImage.TYPE_INT_ARGB Dim g2d As JavaObject = bufferedImage.RunMethod("createGraphics", Null) g2d.RunMethod("setRenderingHint", Array(jo.GetField("KEY_INTERPOLATION"), jo.GetField("VALUE_INTERPOLATION_BICUBIC"))) g2d.RunMethod("setRenderingHint", Array(jo.GetField("KEY_ANTIALIASING"), jo.GetField("VALUE_ANTIALIAS_ON"))) g2d.RunMethod("drawImage", Array(original, 0, 0, newWidth, newHeight, Null)) g2d.RunMethod("dispose", Null) Dim resizedImage As Image = bufferedImage Return resizedImage End Sub

Thanks for the attention.
There are a few errors in the code...

For instace:
Dim bufferedImage As JavaObject = jo.CreateNew(newWidth, newHeight, 2) ' 2 = BufferedImage.TYPE_INT_ARGB
(unknown member: createnew)

I tried a few thinks, but still with errors:

B4X:

Sub ResizeImage(original As Image, newWidth As Int, newHeight As Int) As Image
'    Dim jo As JavaObject
    Dim bufferedImage As JavaObject
    bufferedImage.InitializeNewInstance("java.awt.image.BufferedImage", Array(newWidth, newHeight, 2)) ' 2 = BufferedImage.TYPE_INT_ARGB

    Dim g2d As JavaObject = bufferedImage.RunMethod("createGraphics", Null)

    Dim renderingHints As JavaObject
    renderingHints.InitializeStatic("java.awt.RenderingHints")
    g2d.RunMethod("setRenderingHint", Array(renderingHints.GetField("KEY_INTERPOLATION"), renderingHints.GetField("VALUE_INTERPOLATION_BICUBIC")))
    g2d.RunMethod("setRenderingHint", Array(renderingHints.GetField("KEY_ANTIALIASING"), renderingHints.GetField("VALUE_ANTIALIAS_ON")))

    ' Converter javafx.scene.image.Image para java.awt.Image
    Dim swingFXUtils As JavaObject
    swingFXUtils.InitializeStatic("javafx.embed.swing.SwingFXUtils")
    Dim awtImage As JavaObject = swingFXUtils.RunMethod("fromFXImage", Array(original, Null))

    g2d.RunMethod("drawImage", Array(awtImage, 0, 0, newWidth, newHeight, Null))
    g2d.RunMethod("dispose", Null)

    ' Converter de volta para javafx.scene.image.Image
    Dim resizedImage As Image = swingFXUtils.RunMethod("toFXImage", Array(bufferedImage, Null))
    Return resizedImage
End Sub

B4J Question How to resize and save a captured bitmap without losing quality?

jroriz

Active Member

TILogistic

Expert

[Source code] ImageScaler

jroriz

Active Member

[Source code] ImageScaler

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B4J Question How to resize and save a captured bitmap without losing quality?

jroriz

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TILogistic

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[Source code] ImageScaler

jroriz

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[Source code] ImageScaler

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