01What you’re making
This is a picture rather than a pattern, and that changes how it is built. The wallpaper and the floor are each an ordinary repeating quilt design, pieced flat in blocks exactly as you would piece any quilt. What makes it a room is what happens next: both panels are cut along the lines of the walls and the floor, joined with white strips, and then a bed and three empty pictures are laid over the top.
How hard is it, really
The piecing is no harder than a first quilt: every one of the 2,812 pieces is a plain square, a square made of two triangles, or a square made of four. There are no curves, no set-in seams and no templates in the piecing.
Two things are new. The panels get cut on the diagonal, which leaves stretchy bias edges that need a little care — section 12 is entirely about that. And the bed and pictures are appliqued, which is hand or machine work of a different kind, and forgiving: they are plain shapes in one fabric, with nothing to match.
Progress
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02How the painting is put together
The first thing worth knowing is something the painting does quietly, and it is the reason this quilt is possible at all. The room is drawn in perspective. The patterns are not.
The ceiling line, the skirting board and the corner all behave like a real room seen from one side: they converge, and if you extend them they meet at two vanishing points sitting on a single horizon. But the wallpaper laid over that room never changes size. Its squares measure the same across the whole painting, from the corner to the right-hand edge. Had Erin drawn the wallpaper receding with the room, its squares would have grown by a factor of 3.06 across the right-hand wall, and no flat panel of piecing could reproduce it.
This is what makes the quilt buildable. The wallpaper is a flat repeating pattern. The floor is a flat repeating pattern. The room is the shape they are cut into.
The wallpaper
A 6 × 6 repeat. Four blocks of four plain squares — pink and navy, checkerboarded — separated by lines of hourglass units, with a single plain square where those lines cross. The pink and navy swap over from one four-patch to the next, which is why the repeat is six squares and not three.
The floor
A single tile, 4 × 4 squares, and every tile in the painting is identical. A mitred frame one square deep — green along the top and the right, teal along the bottom and the left — around a two-square hourglass with navy top and bottom and pink either side.
Wallpaper block — 6 × 6 units, 9″ finished. Make 51.
Floor tile — 4 × 4 units, 6″ finished. Make 61.
Four wallpaper blocks together. Half the shapes only appear once the blocks meet.
Four floor tiles together. The green and teal frames run into diagonal ribbons.
Only three kinds of piece
That is the whole vocabulary. A plain square. A triangle unit — two triangles joined on the diagonal, what quilters call a half-square triangle. And an hourglass unit — four triangles, a quarter-square triangle, which is just two triangle units cut apart again the other way.
03Size, and the one formula
One decision sets every other measurement: how big each small square finishes. The whole quilt is 54 squares across and 43 down, so everything follows from that number.
| Each square finishes | Wallpaper block | Floor tile | Whole quilt | Feels like |
|---|---|---|---|---|
| 1″ | 6″ | 4″ | 54″ × 43″ | Small wall hanging |
| 1¼″ | 7½″ | 5″ | 67½″ × 53¾″ | Wall hanging |
| 1½″ | 9″ | 6″ | 81″ × 64½″ | Big picture, or a throw — recommended |
| 2″ | 12″ | 8″ | 108″ × 86″ | Bed-sized |
The rest of this pattern uses 1½″, which gives 81″ × 64½″ — big enough to read as a picture across a room, small enough that the piecing stays sane. It also puts the cut sizes exactly where they are on Pattern, so if you have made that one, none of the cutting will be new.
Three cut sizes, and that is all
Every piece is cut larger than it finishes, because a ¼″ seam eats ¼″ off each side. Three rules cover the entire quilt:
- Plain square finished + ½″ → 1½″ finished means cut 2″
- Triangle unit finished + ⅞″ → cut 2⅜″, then make triangles
- Hourglass unit finished + 1¼″ → cut 2¾″, then make triangles twice
The white strips and the applique shapes are not on this grid — they are cut to fit, and are covered in sections 12 and 13.
04Fabric and shopping list
Use quilting-weight cotton. Four colours do all of the pattern; a fifth — plain white or a soft cream — does the room’s lines, the bed and the pictures. These were read straight off the painting; match them by eye at the shop and don’t agonise over exact shades.
| Fabric | Reads as | Where it goes | Buy |
|---|---|---|---|
| Teal | dusty blue-green | Half of every wallpaper hourglass, and the frame down the left and along the bottom of each floor tile | 4 yd |
| Green | soft grass green | The other half of every wallpaper hourglass, the frame along the top and right of each floor tile, and the ceiling | 4¼ yd |
| Pink | mid rose pink | Half the plain squares in the wallpaper, and the sides of every floor hourglass | 2½ yd |
| Navy | strong royal blue | The other half of the wallpaper, and the top and bottom of every floor hourglass | 2½ yd |
| White | unpainted paper — plain white or cream | The room’s lines, the ceiling and skirting strips, the bed and the three pictures | 2 yd |
| Total | 15¼ yd |
Yardages assume 40″ of usable width once selvedges are trimmed, and include about 15% margin. Teal and green take the most because hourglass units are hungry: a 2¾″ square of each makes only two finished 1½″ units.
Also on the list
| Backing | 2½ yd of extra-wide (89″-plus) backing fabric — much the easier route. Or 6¼ yd of normal-width fabric, pieced from 3 panels. |
|---|---|
| Batting | At least 89″ × 72½″. |
| Binding | ¾ yd — navy looks right, and stops the picture leaking off its own edge. 8 strips cut 2½″ wide. |
| Thread | Fine cotton piecing thread, 50 weight, in a mid grey, plus a reel matching the white for the applique. |
| Also | Fusible web or freezer paper for the applique, spray starch, a rotary blade (a fresh one), a long ruler or a chalk line for marking the room, and a few colour-catcher sheets for the first wash. |
Wash first?
Yes. There is a lot of navy sitting against a lot of white here, and a bed is the largest unbroken piece of white in the quilt — exactly where a bleed would show. Wash and dry each fabric before cutting, and press it flat afterwards.
05Tools and setting up
What you need
- Sewing machine with a ¼″ foot
- Rotary cutter, self-healing mat, and a 6″ × 24″ ruler
- A small square ruler with a 45° line — a 4½″ or 6½″ square — for trimming units
- Something to mark a long straight line with: a chalk line, a hera marker, or a long ruler and a fabric pencil
- Iron, fine pins, a seam ripper, small scissors
Test your seam before anything else
The whole quilt rests on a scant ¼″ seam — a hair under a true quarter inch, to allow for the thickness the fabric takes when the seam is pressed over.
- Cut three scraps 2″ × 2″.
- Sew them into a row and press.
- The row should measure exactly 5″ raw, and the middle square exactly 1½″.
Five minutes here saves a hundred blocks of trouble.
06Cutting
Cut in strips across the width of the fabric, then cut the strips into squares. Keep the three sizes firmly apart — 2″, 2⅜″ and 2¾″ are close enough to confuse and different enough to ruin a block.
| Fabric | 2″plain squares | 2½″for triangle units | 2¾″for hourglass units | Strips to cut |
|---|---|---|---|---|
| Teal | 305 | 61 | 408 | 16 × 2″ 4 × 2½″ 30 × 2¾″ |
| Green | 305 | 61 | 408 | 16 × 2″ 4 × 2½″ 30 × 2¾″ |
| Pink | 510 | 122 | — | 26 × 2″ 8 × 2½″ |
| Navy | 510 | 122 | — | 26 × 2″ 8 × 2½″ |
| Total | 1,630 | 366 | 816 | 2,812 squares |
These are the squares you cut. The triangle and hourglass squares get sewn and cut apart into finished units in section 8 — one pair of 2⅜″ squares makes two triangle units, one pair of 2¾″ squares makes two hourglass units.
Or, one block at a time
If you would rather cut as you go:
| Block | What to cut | Per block | For all of them |
|---|---|---|---|
| Wallpaper× 51 | Pink squares, cut 2″ | 10 | 510 |
| Navy squares, cut 2″ | 10 | 510 | |
| Teal + green squares, cut 2¾″ 8 of each make 16 hourglass units | 8 + 8 | 816 | |
| Floor tile× 61 | Green squares, cut 2″ | 5 | 305 |
| Teal squares, cut 2″ | 5 | 305 | |
| Green + teal squares, cut 2½″ 1 of each makes the 2 corner units | 1 + 1 | 122 | |
| Navy + pink squares, cut 2½″ 2 of each make the 4 middle units | 2 + 2 | 244 |
07Make one of each before you cut everything
Do this first. Cut enough for one wallpaper block and one floor tile, make them, and measure. The wallpaper block should come out at 9½″ square before it is sewn to anything (9″ once it’s in the quilt); the floor tile at 6½″ square (6″ finished).
- Bang on? Cut the rest with confidence.
- Coming up small? Your seam is a touch wide. Nudge the needle.
- Coming up large? Your seam is narrow, or the pieces aren’t pressed fully flat.
The two block sizes have to agree with each other — a 9″ wallpaper block and a 6″ floor tile are both built on the same 1½″ square, and they meet along the skirting board. If one drifts and the other doesn’t, the room stops fitting together.
08Triangle units and hourglass units
Triangle units, two at a time
- Stack a pair right sides together, edges matched — one square of each fabric, cut 2⅜″.
- Draw the diagonal corner to corner on the back of the lighter square.
- Stitch a scant ¼″ away from the line, on both sides. Not on the line — either side of it.
- Cut along the drawn line. Two units.
- Press the seam open, then trim each unit to exactly 2″ square, keeping the 45° line of your ruler on the seam.
Hourglass units, two at a time
An hourglass unit is a triangle unit that has been cut apart a second time, the other way. All 816 of them in this quilt are the same pairing — teal and green — so this is one long batch.
- Pair a teal and a green square, both cut 2¾″.
- Make two triangle units from them exactly as above — but do not trim them.
- Stack the two units right sides together with teal facing green, so the two diagonal seams sit directly on top of one another and nest.
- Draw the other diagonal across the top, stitch a scant ¼″ either side of it, and cut on the line.
- Press open and trim to 2″ square, keeping the centre of the ruler exactly on the point where the four triangles meet.
Don’t skip the trimming
It is the single thing that most determines whether the hourglasses come out sharp. Cutting them a whisker oversized and trimming down is deliberate: it absorbs all the small errors before they reach the block.
Press these seams open rather than to one side. With four seams meeting at the middle of every hourglass, open seams keep the block flat and stop a little pyramid building where the points meet.
| Make | Pairs of squares | Units you get | For |
|---|---|---|---|
| Green + Teal hourglass | 408 of each, cut 2¾″ | 816 | The wallpaper |
| Green + Teal triangle | 61 of each, cut 2½″ | 122 | The mitred corners of each floor tile |
| Navy + Pink triangle | 122 of each, cut 2½″ | 244 | The hourglass in the middle of each floor tile |
| Total | 1,182 units |
09Piecing the wallpaper blocks
51 identical blocks, 6 × 6 units each. Work in rows, like reading a page, and lay all 36 units out before a single seam goes in.
What goes where
Each swatch below is drawn at the orientation the unit is actually sewn. For the hourglass units the picture is the instruction — turn the unit until it matches.
| Row | 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|
| Row 1 | Pink | Navy | Teal ↕ Green ↔ | Navy | Pink | Teal ↕ Green ↔ |
| Row 2 | Navy | Pink | Teal ↕ Green ↔ | Pink | Navy | Teal ↕ Green ↔ |
| Row 3 | Green ↕ Teal ↔ | Green ↕ Teal ↔ | Pink | Green ↕ Teal ↔ | Green ↕ Teal ↔ | Navy |
| Row 4 | Navy | Pink | Teal ↕ Green ↔ | Pink | Navy | Teal ↕ Green ↔ |
| Row 5 | Pink | Navy | Teal ↕ Green ↔ | Navy | Pink | Teal ↕ Green ↔ |
| Row 6 | Green ↕ Teal ↔ | Green ↕ Teal ↔ | Navy | Green ↕ Teal ↔ | Green ↕ Teal ↔ | Pink |
- Sew each row of 6 units, left to right, chain-piecing rather than fetching pieces one at a time.
- Press the row seams. Odd rows to the right, even rows to the left, so that when two rows meet their seams fall opposite ways and lock against each other.
- Join the rows top to bottom, pinning at each nested seam. Press these long seams open.
- Measure. 9½″ square. Set it aside and start the next.
The block reads the same forwards and backwards along every row. If one doesn’t, a unit is turned the wrong way.
10Piecing the floor tiles
61 identical tiles, 4 × 4 units each. Simpler than the wallpaper: ten plain squares, two teal-and-green triangle units at opposite corners, and four navy-and-pink triangle units that make the hourglass in the middle.
| Row | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
| Row 1 | Green / Teal | Green | Green | Green |
| Row 2 | Teal | Navy / Pink | Navy / Pink | Green |
| Row 3 | Teal | Pink / Navy | Pink / Navy | Green |
| Row 4 | Teal | Teal | Teal | Green / Teal |
- Make the middle first. Four navy-and-pink triangle units, arranged with all four navy points meeting at the centre, make the two-square hourglass. Sew them into a four-patch and check the point.
- Sew rows 1 and 4 — the plain edges with a triangle unit at one end.
- Add the side squares to the middle four-patch, then sew the top and bottom rows on.
- Measure. 6½″ square.
The two teal-and-green triangle units sit at the top left and the bottom right, both with the green on the upper right of the diagonal. Get one of them the wrong way round and the diagonal ribbons across the floor break.
11Joining the blocks into two panels
Now build the two panels. Neither is a plain rectangle — you only make the blocks that show — so this is where the map earns its keep.
The wallpaper panel
51 blocks. Sew them edge to edge — there is no sashing, and the design is meant to run straight across the block seams, which is why half the shapes only appear once the blocks are joined.
Piece it in rows of blocks, press the row seams in alternate directions, then join the rows. Where the panel has a stepped edge, sew the short rows on last.
The floor panel
61 tiles, joined the same way. Because the skirting board runs diagonally, the top of this panel is a staircase rather than a straight line; that is fine, it all gets cut off.
Press well and measure as you go. A panel this size that is out of square will not sit flat against a straight cut line.
2,812 units get pieced for a quilt that finishes at 2,322 squares — 21.1% over. That is the cost of cutting a picture out of a pattern: every block along a diagonal is made whole and then trimmed. The offcuts are large, clean, and already pieced; a pair of them makes a cushion front, and the biggest would back a small quilt.
12Cutting the room
Read this section twice before you pick up the rotary cutter. Everything up to here can be unpicked. This cannot.
The room is four straight lines: the ceiling on each side of the corner, and the skirting board on each side of it. Each is marked, cut, and then a white strip is sewn in along it.
Marking
Work on a big flat surface with the panel pressed and square. Measure from the top left corner of the quilt in every case — errors that accumulate along an edge will throw the corner out.
| Line | Fromacross, down | Toacross, down | Length |
|---|---|---|---|
| Ceiling, left of the corner | 4″, 0″ | 23¾″, 3¾″ | 20⅛″ |
| Ceiling, right of the corner | 23¾″, 3¾″ | 39¾″, 0″ | 16½″ |
| Skirting, left of the corner | 0″, 39⅛″ | 23¾″, 34⅛″ | 24¼″ |
| Skirting, right of the corner | 23¾″, 34⅛″ | 81″, 49″ | 59⅛″ |
| The corner of the room | 23¾″ across, from 3¾″ to 34⅛″ down | 30⅜″ | |
Mark the finished line. You will cut ¼″ outside it, on the side that keeps the fabric, so the seam allowance is there when the white strip goes on.
Cutting
- Starch the panel along the line, generously, and press it dry. Starch is what stops a bias edge behaving like elastic. Do not skip it.
- Stay-stitch a line of ordinary machine stitching about ⅛″ outside your cutting line, through the pieced panel. This holds every little seam the cut is about to cross.
- Cut with a long ruler and a fresh blade, in one pass, ¼″ outside the marked finished line.
- Handle the cut edge as little as possible from now on. Carry the panel flat; don’t let it hang.
Putting the room together
The white strips are cut 2″ wide — 1½″ finished — and long enough to run past both ends of each line, which is easier than trying to cut them to length. You need about 138″ of strip in total.
- Ceiling first. Sew a white strip to the top edge of the wall panel along each of the two ceiling lines, mitring where they meet at the corner. Press towards the strip.
- Add the ceiling. One green triangle, 35¾″ along the top edge of the quilt and 3¾″ deep at the corner, cut with a ¼″ seam allowance all round. Sew it to the other side of the white strips.
- Skirting board. Sew a white strip along the bottom edge of the wall panel, again mitring at the corner, and press towards the strip.
- Join the floor. Pin the floor panel to the free edge of that strip, matching the corner first and then easing along each side. Sew, press, and check the whole thing lies flat.
- Square the quilt to 81″ × 64½″, trimming the outer edges.
Why mitre rather than butt. The two ceiling lines meet at the corner at an angle, and so do the two skirting lines. A mitred join puts a single clean point there. Butting one strip against the other leaves a step, and the corner of the room is the first place the eye goes.
13The bed and the pictures
Four shapes in white, laid on top of the finished room. In the painting they are simply unpainted paper — no shading, no detail — and the quilt should be the same: flat white, with the folds suggested by quilting later rather than by piecing now.
| Shape | Finished size | Corners, measured from the top left of the quilt |
|---|---|---|
| Picture 1 left wall | 11½″ × 19⅛″ | 2″, 9⅜″ · 13⅜″, 10⅝″ · 13½″, 27⅜″ · 2⅜″, 28½″ |
| Picture 2 right wall, near the corner | 10⅝″ × 20½″ | 35⅜″, 9¾″ · 45¾″, 8⅜″ · 45⅜″, 28⅞″ · 35¼″, 27½″ |
| Picture 3 right wall, far side | 15⅞″ × 29⅝″ | 64⅝″, 5⅞″ · 80¼″, 3¾″ · 79¾″, 33⅜″ · 64⅜″, 30⅝″ |
| Bed | 37⅛″ × 25⅛″ | Top left of its box at 23⅞″, 34″. Copy the outline from the drawing below. |
The three pictures
None of them is a rectangle — they hang on walls drawn in perspective, so each is a quadrilateral with four different corners. Cut them from the table above, adding ½″ all round if you are turning the edges under.
- Cut the shape to the four corners given, plus your turning allowance.
- Position it using the measurements from the top left corner of the quilt, and pin or press it into place.
- Applique it down — by hand with a blind stitch, or by machine with a narrow zigzag or a blanket stitch in matching thread.
- Mark the inner line. The painting draws a thin pencil rectangle inside each picture, about ¼″ in from the edge. Quilt it in later rather than piecing or drawing it.
The bed
The easiest way to get this shape full size is to draw it on the quilt itself. Chalk the grid lines — they are the block seams you have already sewn, so most of them are there — and copy the outline square by square from the diagram. It does not need to be exact; it is a rumpled bedspread, and a slightly different rumple is still a bedspread.
- Cut the bed from white, adding ½″ all round.
- Place it with its top left corner 23⅞″ from the left edge of the quilt and 34″ from the top.
- Applique it down. Take particular care along the top edge, where it crosses the skirting board — that seam is already bulky and the bed needs to lie flat over it.
- Trim away the back. Once it is stitched, cut the pieced panel out from behind the bed, leaving ¼″ inside the stitching line. It is the largest applique in the quilt and it will be much easier to quilt without four layers under it.
14Backing, batting and basting
The backing
You need a backing about 89″ × 72½″ — 4″ bigger than the quilt on every side.
- Extra-wide backing fabric (2½ yd) needs no piecing at all.
- Normal-width fabric (6¼ yd) means joining 3 panels. Trim the selvedges off first, join with ½″ seams, and press those seams open.
Basting
- Backing down first, wrong side up. Smooth it flat and tape the edges down — taut, but not stretched.
- Batting on top, smoothed from the centre outwards.
- Quilt top on last, right side up, centred, smoothed from the middle.
- Baste with safety pins every 3–4″, or with basting spray. Work from the centre out.
Pin generously along the two diagonal seams. They are the only bias seams in the quilt and they are the most likely to shift while you work.
15Quilting
This top has two busy patterns and four big blank shapes, and that split is worth using rather than ignoring. The usual advice — quilt it all the same — makes the bed look like a hole.
- On the wallpaper and the floor, keep it structural and quiet. Straight lines in the ditch along the block seams, or diagonals through the hourglasses, both disappear into the piecing and hold the layers.
- On the bed, do the opposite: this is where the quilting draws. Long curved lines following the folds of the bedspread, close together, will make it read as cloth rather than as a white gap. The painting’s own pencil lines show where the folds fall.
- On the pictures, quilt the inner rectangle about ¼″ in from the edge, and leave the middle empty. That is exactly what the painting does.
- On the ceiling, whatever you like — it is a small triangle.
Start in the middle and work outwards, so any excess is pushed to the edges rather than trapped in the centre. Don’t leave any area larger than about 4–6″ unquilted, or check what your batting’s packet specifies.
16Binding
You need about 291″ of binding, so cut 8 strips 2½″ wide.
- Trim the quilt square, cutting the batting and backing flush with the top.
- Join the strips end to end with diagonal seams; press those open. Press the whole length in half lengthwise, wrong sides together.
- Sew it to the front with a ¼″ seam, raw edges together, starting partway along one side and leaving a tail of about 10″ loose.
- Mitre the corners: stop ¼″ from each corner, backstitch, fold the binding straight up away from the quilt to make a 45° fold, then fold it back down level with the next edge.
- Join the two ends where they meet — overlap by exactly the width of your binding, trim, and seam them diagonally.
- Turn the binding to the back and stitch it down, covering the line of machine stitching.
17Label, and looking after it
Put a label on it. A scrap of the backing fabric, hemmed and stitched to a back corner, with the maker’s name, the date, and a line about where the design came from — the painting, its title, and Erin’s name. In fifty years that label will be the most valuable part of the quilt.
Hanging it. This one is a picture, and pictures want a wall. A hanging sleeve — a 4″ tube of backing fabric, hemmed at both ends and slip-stitched along the top edge on the back — takes a batten and keeps the weight off the binding. Sew it on before the binding is turned and it hides completely.
Washing. Cold water, gentle cycle, mild detergent. Colour-catcher sheets for the first few washes — there is a lot of navy against a lot of white. Dry flat or on a line.
18When something goes wrong
- My hourglass units have blunt points in the middle.
- Either they weren’t trimmed with the ruler’s centre exactly on the crossing point, or the second cut wandered off the drawn line. There should be a full ¼″ of fabric beyond the centre point on every side before it meets the next seam.
- The cut edge has stretched and now waves.
- Bias. Starch it hard, press it dry without sliding the iron, and ease the extra length in as you pin the white strip on — pin at both ends and the middle first, then halve the gaps. If it is badly out, a line of stay-stitching pulled up very slightly will draw it back.
- The corner of the room doesn’t meet in a point.
- The two white strips need mitring, not butting. Unpick back a few inches either side, fold each strip at 45°, press the fold, and stitch along it.
- The floor panel is longer than the wall panel along the skirting board.
- One of them has stretched on the diagonal, or the room lines were marked from different edges. Measure both cut edges: the true length is the one that matches the table in section 12. Ease the longer one in rather than trimming — trimming moves the line.
- The bed puckers where it crosses the skirting board.
- That seam has three or four layers under it. Press it as flat as it will go before appliqueing, and consider trimming the seam allowances down within the bed’s outline before you stitch it over them.
- I’ve run out of one fabric.
- Teal and green go furthest — they are in every hourglass. If you are short, substitute in the floor tiles rather than the wallpaper: the floor has fewer, larger pieces and a slight shift there reads as light on a floor rather than as a mistake.
19Glossary
- Finished vs unfinished
- Finished is the size a piece ends up once it’s sewn in on all sides; unfinished is its size while it’s still loose. A 1½″ finished square is a 2″ unfinished one.
- Scant ¼″
- A seam a thread or two under a quarter inch, allowing for the fabric taken up when the seam is pressed over.
- Half-square triangle (HST)
- A square made of two triangles joined on the diagonal. Called a “triangle unit” throughout this pattern.
- Quarter-square triangle (QST)
- A square made of four triangles meeting at the centre. Called an “hourglass unit” here.
- Bias
- Any line at 45° to the weave. Bias edges stretch; straight-grain edges don’t. Every cut in section 12 crosses the grain at an angle, which is why they all get starched.
- Stay-stitching
- A line of ordinary stitching sewn just outside a cutting line to stop the seams it crosses from opening up.
- Applique
- A shape laid on top of a finished background and stitched down, rather than pieced into it.
- Mitre
- A join made at 45°, so two strips meeting at a corner form a clean diagonal seam.
- Nesting
- Pressing two seams that will meet in opposite directions, so they lock together and the join lines up.
- WOF
- Width of fabric — a cut running selvedge to selvedge, about 40″ usable.
20How these numbers were worked out
Nothing here was estimated by eye. The painting was measured directly, and the design was drawn back out and compared against it.
- The room was found by fitting all four white lines at once from six numbers — a horizon, two vanishing points, the corner, and the height of the wall at the corner — so that they are forced to describe a real room rather than four independent lines. 336 points on those lines fit to 1.55 pixels rms, and the two vanishing points land on the same horizon to within 2 pixels.
- The patterns were tested for perspective by measuring their repeat in a sliding window across the whole painting. The wallpaper measures 33–37 pixels everywhere. If it followed the room it would grow 3.06× across the right-hand wall. It does not, so both patterns are flat.
- The wallpaper’s repeat was confirmed by shift-matching the map of cells against itself: cells agree 0.77 of the time six cells apart, against 0.2–0.4 at every other shift — and the agreement holds across the room’s corner, which is how we know the wall is one continuous flat panel and not two.
- Each block is a majority vote, pixel by pixel, across every repeat of it in the painting — 785 wallpaper cells and 25 floor tiles. That averaging is what recovers the intended design from a hand-painted one.
- The design was drawn back out at the painting’s own size and compared to it. 98% of the painting agrees on where the white is — the room’s lines, the pictures and the bed — and 68% of pixels get the same fabric, against a hand-painted original with a pencil line around every piece.
What was changed on purpose
Three regularisations, and they are the only places where the quilt departs from the painting:
| 1 | The grid is 54 x 43 cells. The painting measures 54.3 x 43.5, so the outer edge is trimmed by about a third of a cell. |
|---|---|
| 2 | The floor tile is set at exactly 4 cells square. Measured, it is 3.89 cells wide and 3.99 deep — the two grids were ruled independently and do not quite agree. |
| 3 | The wallpaper grid is treated as starting square with the top left corner. Measured, it starts a quarter of a cell in. |
Two further choices are judgement rather than measurement: the 1½″ finished square, and the decision to applique the bed and the pictures rather than piece them in. Both are easy to change.