The scale node use a multiplier, 0.5 to reduce the image size by half and 2 to increase by 2. What should i use if i want to convert any image source at the desired resolution, for example i want to input a 4096*4096 or 512*512 and always get a 1024*1024 output and get the entire image not cropped.
You can set the Resolution Size (in pixels) to the desired output size in the Scene Dimensions section of the properties window..
Using a Scale Node, will rescale an image connected to it to the predetermined output resolution.
If you want to double the number of pixels just render at 200% (in this example rendering a 512 x 512 pixel image will result in an image of 1024 x 1024 pixels). To cut the number of pixels in half, render at 50%.
Note that if the images are a different aspect ratio than the output, you have three choices:
stretch: deform the image to match within the aspect ratio of the container)
Fit: keep the images proportions but fill the remaining either with a transparent background or with black (if the "Use Alpha" option is unchecked)
or Crop Not stretching the image, resizing to fit vertically center cropping horizontally.