Dividing a photograph into four pieces sounds like a matter of halving its width and height. That works neatly when both dimensions are even. A 401 by 301-pixel image is less cooperative: half a pixel is not a useful boundary for an exported raster tile. If every piece is rounded down independently, an edge can disappear.

The reliable approach is to calculate shared boundaries first and derive each tile from the space between them. It turns an awkward remainder into an ordinary part of the grid. You can then check the exported pieces mathematically before worrying about their display order or print arrangement.

Boundaries, rather than repeated tile sizes

For an image width W divided into C columns, define boundary i as floor(i × W ÷ C), where i runs from zero through C. Each tile starts at one boundary and ends at the next. The first boundary is zero and the last is exactly W. Because adjacent tiles share a boundary, there is neither a gap nor an overlap in source coordinates.

Take W equal to 401 and C equal to two. The boundaries are zero, 200 and 401. The two widths are therefore 200 and 201 pixels. For a height of 301 divided into two rows, the boundaries are zero, 150 and 301, producing heights of 150 and 151. Four tiles together account for the complete source rectangle.

This is a calculation about existing pixels, not an instruction to stretch the image. The Canvas drawImage documentation describes drawing a selected source rectangle into a destination. Handyfold uses source rectangles with matching destination sizes for its grid tiles, so the cut does not need to invent a fractional edge pixel.

Run a case where rounding matters

Open Split image into tiles and select Load example. Its image is 401 by 301 pixels specifically so a two-by-two split has remainders. Leave Rows and Columns at two, then run the tool. Download the four PNG files and inspect their dimensions.

The first row contains a 200 by 150 tile and a 201 by 150 tile. The second row contains a 200 by 151 tile and a 201 by 151 tile. The filenames identify row and column. Read tile-1-2 as row one, column two, rather than as a chronological version or a single flattened index.

For another check, add the widths across either row and the heights down either column. They should reproduce the original dimensions. You can also compare the total pixel count: the sum of the four rectangular areas should be 120,701, which equals 401 multiplied by 301. That accounting catches an omitted edge even if the missing strip is difficult to notice visually.

Reconstruction is a different layout task

To reconstruct the original image, place the tiles at their original boundaries without adding spacing, borders or independent resizing. A layout that gives every tile the same displayed width may rescale the 201-pixel column differently from the 200-pixel column. The exported source partition can be correct while the reconstructed display develops a seam.

Inspect a recognizable feature that crosses a boundary, such as a diagonal line or an object’s outline. Confirm that it continues without a jump. Then inspect the outside edges, where a missing final strip would appear. A photograph with a plain background can hide a layout error, so the dimensional check remains useful even when the preview looks plausible.

The Adobe explanation of pixel dimensions and resampling helps distinguish changing a layout from changing its raster data. If a publishing system resizes each upload, check its actual behavior after placement. The grid splitter cannot control transformations performed later by another application.

Decide whether unequal edges are acceptable

Some destinations require every tile to have identical dimensions. In that case, choose an original canvas whose dimensions divide evenly by the requested grid, or deliberately prepare a new canvas. Cropping removes material; padding adds a border area; resizing changes the image’s pixel representation. Select one knowingly rather than calling every approach a lossless split.

A print assembly introduces further constraints. The Handyfold splitter does not add overlap, trim marks or allowances for a printer’s unprintable margins. If you need adjacent sheets to overlap for mounting, use an appropriate print-tiling workflow. Cutting a photograph into source rectangles and preparing physical poster sheets are related ideas with different output requirements.

Keep the tile set together

Check the file count too. A grid with three rows and four columns needs twelve files, even when several pieces contain nearly identical background colors. Similar-looking thumbnails should not be mistaken for redundant exports.

Store all tiles in one clearly named folder and preserve their row-column filenames. Before handing them off, state the source dimensions, grid size and intended placement order. Do not rely on a recipient guessing whether the sequence runs across rows or down columns.

Finally, keep the unsplit original. A collection of correctly sized pieces can reconstruct its pixels, but it is less convenient for future edits and may not retain the original file’s metadata. The shared-boundary method gives you a precise partition; the dimensional checks and placement instructions make that precision survive the next step in the workflow.