change live preview format to jpeg to prevent unreasonably slow previews for...

change live preview format to jpeg to prevent unreasonably slow previews for large images, and add an option to let user select the format

modules/progress.py

@@ -95,9 +95,9 @@ def progressapi(req: ProgressRequest):
         image = shared.state.current_image
         if image is not None:
             buffered = io.BytesIO()
-            image.save(buffered, format="png")
+            image.save(buffered, format=opts.live_previews_format)
             base64_image = base64.b64encode(buffered.getvalue()).decode('ascii')
-            live_preview = f"data:image/png;base64,{base64_image}"
+            live_preview = f"data:image/{opts.live_previews_format};base64,{base64_image}"
             id_live_preview = shared.state.id_live_preview
         else:
             live_preview = None

modules/shared.py

@@ -420,6 +420,7 @@ options_templates.update(options_section(('infotext', "Infotext"), {
 options_templates.update(options_section(('ui', "Live previews"), {
     "show_progressbar": OptionInfo(True, "Show progressbar"),
     "live_previews_enable": OptionInfo(True, "Show live previews of the created image"),
+    "live_previews_format": OptionInfo("jpeg", "Live preview file format", gr.Radio, {"choices": ["jpeg", "png", "webp"]}),
     "show_progress_grid": OptionInfo(True, "Show previews of all images generated in a batch as a grid"),
     "show_progress_every_n_steps": OptionInfo(10, "Show new live preview image every N sampling steps. Set to -1 to show after completion of batch.", gr.Slider, {"minimum": -1, "maximum": 32, "step": 1}),
     "show_progress_type": OptionInfo("Approx NN", "Image creation progress preview mode", gr.Radio, {"choices": ["Full", "Approx NN", "Approx cheap"]}),