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yllan / JXLook

JPEG-XL viewer on macOS
MIT License
69 stars 7 forks source link

DPI? Does JXL have scale factor information? #6

Open yllan opened 3 years ago

yllan commented 3 years ago

PNG

image

JPEG-XL Info JxlBasicInfo(have_container: 0, xsize: 244, ysize: 76, bits_per_sample: 8, exponent_bits_per_sample: 0, intensity_target: 255.0, min_nits: 0.0, relative_to_max_display: 0, linear_below: 0.0, uses_original_profile: 1, have_preview: 0, have_animation: 0, orientation: __C.JxlOrientation(rawValue: 1), num_extra_channels: 1, alpha_bits: 8, alpha_exponent_bits: 0, alpha_premultiplied: 0, preview: __C.JxlPreviewHeader(xsize: 0, ysize: 0), animation: __C.JxlAnimationHeader(tps_numerator: 0, tps_denominator: 0, num_loops: 0, have_timecodes: 0))

Evertt commented 3 years ago

I was wondering this too, because when I tried to compare a jxl image using your app to its source jpg image in Preview, I clicked the menu item View -> Actual Size in both apps and I got different zoom levels in both apps, which seemed weird to me.

yllan commented 3 years ago

cjxl and djxl currently didn't preserve the DPI information. I compress a 144 DPI png to jxl and then use djxl to decompress, it becomes a 72 DPI png.

Now I hardcoded the DPI to be 144 (@2x). Will change back to 72 DPI in the next release.

Evertt commented 3 years ago

cjxl and djxl currently didn't preserve the DPI information.

Did you already open a ticket for that on the official jxl repo? Or do you think they already have that on their todo list, but that they just haven't gotten to it yet?

yllan commented 3 years ago

I opened an issue for this: https://gitlab.com/wg1/jpeg-xl/-/issues/123

jonsneyers commented 3 years ago

Currently cjxl silently strips exif/xmp from a PNG, and only encodes the pixel data and the ICC profile.

I didn't know Preview actually looks at DPI information to do "Actual size". I would expect "Actual size" to just show me pixels in native resolution (1:1). It would make sense to use DPI for that and have actual physical dimensions on the screen that match the intended physical dimensions, if it weren't for the fact that most DPI values are bogus default values that are ignored by most software, and have little to do with intended physical dimensions (which is a weird concept anyway, one that is relevant for print but not really for screen display imo).