Add option to img2imgalt.py to use sigma adjustment instead of original method for #736

    return x / x.std()

Cached = namedtuple("Cached", ["noise", "cfg_scale", "steps", "latent", "original_prompt", "original_negative_prompt"])

Cached = namedtuple("Cached", ["noise", "cfg_scale", "steps", "latent", "original_prompt", "original_negative_prompt", "sigma_adjustment"])

# Based on changes suggested by briansemrau in https://github.com/AUTOMATIC1111/stable-diffusion-webui/issues/736

def find_noise_for_image_sigma_adjustment(p, cond, uncond, cfg_scale, steps):

    x = p.init_latent

    s_in = x.new_ones([x.shape[0]])

    dnw = K.external.CompVisDenoiser(shared.sd_model)

    sigmas = dnw.get_sigmas(steps).flip(0)

    shared.state.sampling_steps = steps

    for i in trange(1, len(sigmas)):

        shared.state.sampling_step += 1

        x_in = torch.cat([x] * 2)

        sigma_in = torch.cat([sigmas[i - 1] * s_in] * 2)

        cond_in = torch.cat([uncond, cond])

        c_out, c_in = [K.utils.append_dims(k, x_in.ndim) for k in dnw.get_scalings(sigma_in)]

        if i == 1:

            t = dnw.sigma_to_t(torch.cat([sigmas[i] * s_in] * 2))

        else:

            t = dnw.sigma_to_t(sigma_in)

        eps = shared.sd_model.apply_model(x_in * c_in, t, cond=cond_in)

        denoised_uncond, denoised_cond = (x_in + eps * c_out).chunk(2)

        denoised = denoised_uncond + (denoised_cond - denoised_uncond) * cfg_scale

        if i == 1:

            d = (x - denoised) / (2 * sigmas[i])

        else:

            d = (x - denoised) / sigmas[i - 1]

        dt = sigmas[i] - sigmas[i - 1]

        x = x + d * dt

        sd_samplers.store_latent(x)

        # This shouldn't be necessary, but solved some VRAM issues

        del x_in, sigma_in, cond_in, c_out, c_in, t,

        del eps, denoised_uncond, denoised_cond, denoised, d, dt

    shared.state.nextjob()

    return x / sigmas[-1]

class Script(scripts.Script):

        cfg = gr.Slider(label="Decode CFG scale", minimum=0.0, maximum=15.0, step=0.1, value=1.0)

        st = gr.Slider(label="Decode steps", minimum=1, maximum=150, step=1, value=50)

        randomness = gr.Slider(label="Randomness", minimum=0.0, maximum=1.0, step=0.01, value=0.0)

        return [original_prompt, original_negative_prompt, cfg, st, randomness]

        sigma_adjustment = gr.Checkbox(label="Sigma adjustment for finding noise for image", value=False)

        return [original_prompt, original_negative_prompt, cfg, st, randomness, sigma_adjustment]

    def run(self, p, original_prompt, original_negative_prompt, cfg, st, randomness):

    def run(self, p, original_prompt, original_negative_prompt, cfg, st, randomness, sigma_adjustment):

        p.batch_size = 1

        p.batch_count = 1

        def sample_extra(conditioning, unconditional_conditioning, seeds, subseeds, subseed_strength):

            lat = (p.init_latent.cpu().numpy() * 10).astype(int)

            same_params = self.cache is not None and self.cache.cfg_scale == cfg and self.cache.steps == st and self.cache.original_prompt == original_prompt and self.cache.original_negative_prompt == original_negative_prompt

            same_params = self.cache is not None and self.cache.cfg_scale == cfg and self.cache.steps == st \

                                and self.cache.original_prompt == original_prompt \

                                and self.cache.original_negative_prompt == original_negative_prompt \

                                and self.cache.sigma_adjustment == sigma_adjustment

            same_everything = same_params and self.cache.latent.shape == lat.shape and np.abs(self.cache.latent-lat).sum() < 100

            if same_everything:

                shared.state.job_count += 1

                cond = p.sd_model.get_learned_conditioning(p.batch_size * [original_prompt])

                uncond = p.sd_model.get_learned_conditioning(p.batch_size * [original_negative_prompt])

                if sigma_adjustment:

                    rec_noise = find_noise_for_image_sigma_adjustment(p, cond, uncond, cfg, st)

                else:

                    rec_noise = find_noise_for_image(p, cond, uncond, cfg, st)

                self.cache = Cached(rec_noise, cfg, st, lat, original_prompt, original_negative_prompt)

                self.cache = Cached(rec_noise, cfg, st, lat, original_prompt, original_negative_prompt, sigma_adjustment)

            rand_noise = processing.create_random_tensors(p.init_latent.shape[1:], [p.seed + x + 1 for x in range(p.init_latent.shape[0])])

        p.extra_generation_params["Decode CFG scale"] = cfg

        p.extra_generation_params["Decode steps"] = st

        p.extra_generation_params["Randomness"] = randomness

        p.extra_generation_params["Sigma Adjustment"] = sigma_adjustment

        processed = processing.process_images(p)