Create a TImage from scratch

ROOT
1

Hi,

I am trying to create a PNG image from scratch using the TImage class.

I can import easily a PNG image into TImage, using

TImage *img = TImage::Open(“file.png”);

I can then modify the image directly using i.e. PutPixel( x, y, color )

And I can Draw it without problems.

However, if I do

TImage *img = new TImage( 60, 60 );

I define the pixels color using

for( int n = 0; n < 60; n++ ) for( int m = 0; m < 60; m++ ) img->PutPixel( n, m, "#0000FF");

but then when I try to draw img->Draw(); it shows nothing on the canvas.

There is something else missing?

Thanks!

2

Do you have a small running script showing the problem ?

3

NewPNG.C (275 Bytes)
LoadPNG.C (228 Bytes)

Here I send two macros. LoadPNG works as I expect. But NewPNG does not.

4

Your macro is wrong. In the 2nd loop at line 12 “m” is not defined.

5

Just replace the “m” by a number between 0 and 59. The problem is still not solved.

6

I tried to mimic what is done in TImageDump. But until now I have no success with your macro.
The only way I found working was to load and white image from a png file.

7

Ok, it seems my problem is solved by using TImage::Create and SetImage.

I attach the macro that finally did it.

NewPNG2.C (321 Bytes)

8

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