Add CLI image variations

[monstruosoft]

Add CLI image variations mode by setting the img2img argument without writing a prompt.

This commit also defines two new CLI arguments:
strength, used to define the image variation denoising strength.
batch_count, used to define the number of times that image generation will be run; on low end PCs with low RAM, it might be better to generate, for example, 4 batches of 1 image than 1 batch of 4 images. Total number of generated images should be batch_count * number_of_images.

[monstruosoft]

I have now added to the CLI branch a basic tiled upscale option that upscales the input image using the image variations mode. Please note that it's currently hardcoded to perform a 2x upscale using 512x512 output tiles. Also note that, since there's no guarantee for image variations tiles to be consistent, it's recommended to use a low denoising strength, the default value of 0.3 might be a good start.

[rupeshs]

@monstruosoft Nice work, I will review it later

[rupeshs]

@monstruosoft could you please share some inputs/outputs of tiled upscale?

[monstruosoft]

Sure, here's a couple of, somewhat cherrypicked, examples:

Original:

Upscaled:

Original:

Upscaled:

The upscaled versions were done using SD Turbo 1 step inference for each tile. Note that this is just a basic attempt at doing tiled SD upscale using FastSD CPU and it can be improved; for example, the black bars in the images are caused by the transparency used to try and make the tile seams less noticeable but those black bars can be removed relatively easy. Also, I didn't want to mess with the actual image generation code so currently the individual tiles are saved as well as the final images. Also, output path is currently hardcoded as results.

[rupeshs]

@monstruosoft Yes, there is room for improvement. We can keep this as experimental.