If your downsample is 1, that is the “best” pixel size you can get. You are exporting it at the true resolution of the original image.
If the image is at 0.5um resolution, that is what a downsample of 1 will give you. If your image has 0.29um per pixel resolution, a downsample of 1 will give you that instead. I don’t think the accuracy of a model will be improved much by subdividing pixels. Usually the limitation will be the JPEG encoding, or whatever compression was used to make the whole slide image.
" With each iteration of the file save, the JPEG artifacts compound one another, further degrading the image. On careful examination, lower quality factor JPEG images typically have an artifact of 8 × 8 pixel squares (96
), also known as a macroblock (see Fig. 7c
). In many cases, a more suitable alternative to JPEG is the loss-less PNG file format, although PNG does not support conversion to CYMK for printing (102
). PNG is greatly preferred over JPEG when compressing figures that have small text or fine lines, since it does not blur the edges of these small items."
Even if your final format is TIFF or PNG, if it passed through a JPG stage at some point, you will see those 8x8 blocks, which will limit the accuracy of the classifier on fine objects.
Note that JPEG compression of some sort is very common in whole slide images, despite the problems it causes, due to the file sizes.
Pixel size: If your tiles are 10um and 40 pixels on a side, that give syou a resolution of 0.25um per pixel.
This is higher than the resolution of the 299 pixels at 0.5um; those tiles are also about 150um on a side, so much larger.