Preview

The preview area is where you judge whether a conversion looks right before you spend time exporting it. It has two views, a zoom control, and a flip that is the most useful single tool in the app for spotting dither problems.

Split view and single view

By default the preview is split: the source pane on the left, the result pane on the right, sharing one zoom level and one pan position so a feature lands at the same screen position in both. Press V to collapse to a single canvas showing the result, and press it again to go back to split. V works every time you press it, including several presses in a row with no click in between.

The toolbar names whichever mode you are in: "Split view - V collapses to one canvas" in split view, and "Showing RESULT - hold Space for the source, V for split view" in single view.

V is used rather than the more obvious TAB because egui's own focus navigation consumes the first TAB press as a move between widgets rather than delivering it as a plain key press - so TAB stops doing anything useful after you have clicked into a control once. V has no competing meaning in the app, so it is used instead.

Holding Space to flip

In single view, hold Space to see the source in place of the result - the toolbar changes to "Showing SOURCE - release Space for the result", and releasing the key brings the result straight back. The image does not move, resize or shift by even a pixel between the two; both are drawn at the exact same size and position, because the source pane already shows the framed and adjusted image rather than the raw file (see Getting started).

This is deliberate, and it is the reliable way to judge what dithering did to a picture: flipping two registered images in the same screen position reveals dithering artefacts - noise, banding, worming - far more clearly than looking at the two panes side by side, where your eye has to jump between two different positions to compare them. Pick one small, high-contrast feature - a corner, an eye, an edge - and watch only that while you flip, rather than trying to take in the whole frame at once.

Zoom

Five zoom presets are available, 1x through 5x, with 2x as the default when an image is opened. Click a preset in the toolbar, or scroll the mouse wheel while the pointer is over a preview canvas - scrolling anywhere else, including over the control rail, does not zoom. Zooming stops at 1x and 5x rather than wrapping.

Every zoomed pixel is drawn as a hard-edged block with nearest-neighbour scaling, never smoothed, so you are looking at the actual pixels the Next will display rather than an interpolated approximation of them.

4:3 display aspect

The Next's 320-pixel-wide Layer 2 mode uses non-square pixels: a 320x256 picture fills a 4:3 screen, so each pixel is drawn slightly wider than it is tall on real hardware. Tick 4:3 display aspect to see the picture stretched to that same ratio in the preview; the canvas gets wider without getting taller. Leave it unticked to see the picture at one screen pixel per image pixel instead. A 256x192 picture is already 4:3, so the toggle makes no visible difference to it.

Panning

Drag inside a canvas to pan. In split view both panes pan together, so they stay registered with each other exactly the way they stay registered under zoom.

Known limitations

Zoom keeps the top-left corner of the canvas anchored rather than zooming in on whatever is under the pointer, so the region you are looking at can drift away from the pointer as you zoom in. There is also no reset-view or fit-to-window control, so at higher zoom levels - a 320x256 picture is 1600x1280 physical pixels at 5x - it is easy to pan the image entirely out of view and have to drag it back by eye.