Checks

The checks help you find what's hard to see in a busy picture: weak contrast, single pixels left by a slip of the hand, uneven steps in a line. They mark what they find over the picture; some can fix it too. You can paint as usual with any of them on.

All of them are in View ▸ Checks:

Edit ▸ Clean up strays fixes the stray pixels, in the selection or the whole picture.

The checks belong to the view, not the picture: they aren't saved with a project, and turning one on or off isn't a step in the history. The tracing's opacity and its Over or Under choice, the Specks option and whether the card is folded are remembered for next time.

#The Checks card

While a check is on, a card in the canvas's top left corner shows it, in the Result and Compare views. It has a row for each check that's on (all but Mark hand edits, which needs none), with what it found and its few settings. Each row's × turns that check off.

• ▴ folds the card to a pill that still shows the counts; click the pill to open it again.
• In a small window, where the card would cover more than a third of the picture, it opens folded.
• With the format guides on, the card moves clear of their rulers.

#Brightness only

View ▸ Checks ▸ Brightness only (Y) shows the picture in grays: how C64 artists check contrast and readability. A picture that reads well in gray reads well in color. Painting works as usual, in the real colors.

The Brightness row on the card switches between two kinds of gray:

• Lightness: each color as the gray of its own lightness (CIELAB L*) in the palette you're using. Y turns this on, and off again.
• 9 levels: the VIC-II's 9 luma levels. The C64's video chip gives its 16 colors only 9 brightnesses (the very first VIC-IIs only 5), and the colors that share one show as one gray. Shift+Y turns this on, and off again.

The 9 levels, darkest first:

Why it matters: two colors of the same level mix without a brightness pattern, so a dither or a checkerboard between them looks smooth on a real C64, especially on a TV. Two colors you meant to contrast that turn out to share a level won't stand apart.

The tracing, when it's on, is grayed too.

#Stray pixels

View ▸ Checks ▸ Mark stray pixels rings every stray pixel in cyan. A stray is a pixel with no neighbor of its own color among the 8 around it, where a slip of the hand leaves one.

The finder leaves alone what is lone on purpose:

• pixels in a regular pattern: a checkerboard, an ordered dither;
• grain that comes in crowds, as error diffusion makes;
• pixels whose lightness is between their neighbors': anti-aliasing on an edge, a step of a shading ramp.

It still marks a lone pixel lighter or darker than everything around it, so a highlight or a star is marked too. Whether it's a mistake is your call.

The strays row on the card counts them and has its options:

• Specks: also mark specks, two touching pixels of a color with no other of it around, ringed in orange (and clean them up too). Off at first; remembered.
• Fix by click: when on, a plain click on a stray (or speck) fixes it alone, with any tool in hand but the Eyedropper, as one step in the history. A click beside it paints as usual. Off: the tools paint as usual, rings or not. When you're zoomed out, the area that takes the click is widened to about 3 screen pixels, so you can still hit a stray.
• Clean up (or Clean up selection with a selection): fixes them all, as below.

#Cleaning up

Edit ▸ Clean up strays, or the card's Clean up button, gives each stray the color most of its neighbors have:

• With a selection, only in the selection. Without one, all over the picture; if that would fix more than 10, it asks first, since some may be on purpose.
• Specks too, when the marks are on and Specks is ticked.
• The cell limits are kept the way Edit ▸ Cell limits says, as for any painting.
• A pixel that goes back to the conversion's own color stops being a hand edit.
• It's one step in the history. A message says how many were fixed, with a Show button that flashes them.

It's disabled while a floating piece is out: place it first.

#Jaggies

View ▸ Checks ▸ Mark jaggies boxes each step of a staircase that's out of line with the steps beside it, in yellow over a light wash, and the card counts them. A staircase is a 1-pixel line, or the edge between two areas. A jaggy is a step like the 1 in 3-3-1-3-3, or in 1-2-1-3: the kind of unevenness that makes a line look broken.

It's a heuristic, and careful about what it judges:

• Only clean lines and edges: two colors, or three where the third runs along the edge as an outline or a shading band. Never dithers or noisy areas.
• Steady curves (steps like 1-1-2-3-5) and straight lines made of two step lengths (2-2-3-2-2-3) pass.

There's no automatic fix: a jaggy is fixed by moving a pixel or two by hand.

#Trace the source

View ▸ Checks ▸ Trace the source (Shift+O) lays the source picture over your painting, faint, exactly where the framing puts it. It's for painting from the source by hand, or redrawing a part the conversion lost. It's drawn in the Result view only, and needs a source picture: with a blank picture it's disabled.

The Trace row on the card has:

• Over: the source over the whole picture.
• Under: the source over the conversion only, with your hand edits on top of it. What you've painted stays clear, and the rest shows the source to paint from.
• A slider for the source's opacity: 5% to 100% (40% at first). Double-click it to go back to 40%.

The tracing follows the framing exactly, including the FLI bug's columns, so it lines up with the pixels at any zoom.

#Related

• Overlays: the grids, guides and hand edits.
• The views: the Compare view shows the source beside the result instead.
• Cell limits and clashes: the other thing outlined over the picture.