private void bumpPosition() {
		++xCur;
		if (xCur == imgW) {
			xCur = 0;
			if (!wantInterlaced)
				++yCur;
			else
				switch (curPass) {
					case 0:
						yCur += 8;
						if (yCur >= imgH) {
							++curPass;
							yCur = 4;
						}
						break;
					case 1:
						yCur += 8;
						if (yCur >= imgH) {
							++curPass;
							yCur = 2;
						}
						break;
					case 2:
						yCur += 4;
						if (yCur >= imgH) {
							++curPass;
							yCur = 1;
						}
						break;
					case 3:
						yCur += 2;
						break;
				}
		}
	}