Where does the extra pixel go in a center crop?

A 9 × 6 input with two 6 × 6 outputs

We made a tiny RGB test image whose colors encode its source coordinates. Its columns are numbered 0 through 8 and rows 0 through 5. For the first output we kept columns 1 through 6. For the second we kept columns 2 through 7. Both kept every row. Each output therefore contains exactly 36 pixels, with no pixel blending.

Download the exact PNG files: 9 × 6 source, 6 × 6 starting at column 1, and 6 × 6 starting at column 2. They are deliberately tiny diagnostic images, not photographs. View them with a nearest-neighbor pixel zoom if you want to inspect the cells.

We decoded both saved outputs and compared each pixel with its specified source coordinate. All 36 pixels in each output matched the intended source region. Comparing the two outputs at the same output coordinates, all 36 pixels differed because the source pattern changes at every column. That result establishes the placement difference in this test; it does not mean every photograph would have 36 visibly different pixels.

The rule we used, written explicitly

Let W be the source width and C the smaller crop width. The number of discarded columns is D = W − C. Our first choice removes L = floor(D ÷ 2) columns on the left and R = D − L on the right. If D is odd, the right side loses one more column. The alternative starts one column later, reversing that imbalance. Neither rule is asserted to be the rule of every image editor.

For the 9-to-6 example, D = 3 and L = 1. The crop occupies the boundary interval [1, 7), whose center is 4. The source occupies [0, 9), whose center is 4.5. The crop frame is therefore half a source pixel to the left. The alternative [2, 8) has center 5, half a pixel to the right. The two frame centers are one full source pixel apart, although each is only half a pixel from the ideal center.

Six worked horizontal cases

The table applies the same floor-left rule to every row. Center shift is the crop-frame center minus the source-frame center, measured in source pixels. Negative means left. These are calculated placements, not measurements of any online cropper.

The 1,201-to-800 case removes 401 columns: 200 left and 201 right. Its frame shift is −0.5. The 1,200-to-800 case removes 400: 200 on each side, so its shift is zero. It is the parity of the discarded amount that decides this tie, not whether the output width alone is odd or even.

Check your own pair of widths

Enter the source width and the crop width. This calculator reports our integer floor-left placement and its center shift. It does not process a photo or predict another tool’s default.