Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 169)

JPEG/HEIF Quality
1.
Select [ : quality].
2.
Select the desired image size.
Select the image size, then press < >.
3.
Set the desired quality (compression).
Select the number, then press < >.
Higher numbers offer higher quality (lower compression).
Quality of 6–10 is indicated by < >, and 1–5, by < >.
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