Crop module aspect ratios cleanup + lighttable aspect ratio unification

Is your feature request related to a problem? Please describe.

I noticed that the aspect ratios seem to be a bit confusing to use (of course I can only speak for myself). These could be mulitple Github issues, but I think they have common problems, so I think as a discussion point, a single issue is better.

Crop module presets:

Many of the built-in aspect ratios have too many descriptions or are not so consistent between each other.

• 5:4, 4x5, 8x10. Yes, I understand that they are all valid formats and commonly used paper sizes, but basically they are all the same aspect ratio: 4x5. I think that everybody who knows about 4x5 paper size, will also know about 8x10 paper size and understand, that it is the same aspect ratio.
• What is 10:8 in print? The naming is confusing, especially because the 1.2 ratio here is not 10:8.
• The whole ISO 216 description is imho misleading. I can only speak for myself, but the first time I even learned that there is a ISO 216 standard is... well because I read it in Darktable's crop module. I would argue the common terminology is just "A4". Everybody should know about it (Maybe it's not so common in the US, but then on the other hand: Who knows about letter size outside of the US?).
• 4:3 lists VGA and TV... But who is still using VGA? Even TVs are nowadays all 16:9. On the other hand, Micro Four Thirds is missing, which I guess is more relevant for photographers?
• 3:2, 4x6, 35mm. Here also, 4x6 is basically the same thing as 3:2, just other way around. 35mm okay, but isn't Full Frame or APS-C more relevant for digital photographers? 35mm shooters will know that it's the same aspect ratio as full frame.
• Some other aspect ratios are missing, for example Japanese postcard size (148:100mm).

Manual aspect ratio specification missing

One additional issue is that I cannot manually define an aspect ratio. I can only select freehand, but then I have to deal with percentage sliders from the borders. I cannot just specify 7:10 or 1:14 and then get a fixed ratio crop window to move around.

Lighttable

Furthermore, the Aspect Ratio filter in the Lighttable does not use the same aspect ratios and just displays them as fractions. It also does not clearly show whether an image is landscape or portrait orientation.

For example, on an collection with full frame camera images, the filter is showing 1.5 and 0.7. I can still understand 1.5, but 0.7 is imho a bit confusing. (Btw, the filter uses point as a decimal separater, the crop module uses comma. At least on my German system.)

Describe the solution you'd like

I think it would be nice if the list shows for every entry just one description, maybe with a single additional information in exceptional cases.

Furthermore, I think not every aspect ratio which is currently there needs to be in the list. Instead, I would add an entry to "manually enter aspect ratio". This would reduce the size of the list and probably be easier to use than the current freehand.

Well, here's a personal list as a starting point which I think is more understandable and without cluttering the UI. I would be open for discussions :)

• Freehand
• Define ratio
• Original image (maybe display the aspect ratio of the current image?)
• Square
• 4:5
• Letter
• Micro Four Thirds (4:3)
• 5x7
• A4
• Full Frame (3:2)
• 16:10
• Widescreen (16:9)
• Movie Widescreen
• 2:1 Panorama
• Cinemascope
• 3:1 Panorama

My reasons for removing the following from the list:

• 10:8 in print: The name is misleading, because it is not 10:8. I couldn't find any reference about this online.
• 11x14 - Also I think it's not really often use, at least I have not seen it.
• 45x35, portrait: This is apparently the size of a portrait image for biometric photos in many EU countries. But first, it's the same size as Letter, and second I think that the naming is weird. I think it should be better then named 45x35mm. Portrait is imho not really helpful, because isn't portrait orientation anyway everything in portrait orientation? Why is 1.25 not a portrait?
• Golden Cut: I think maybe golden ratio is better, but not sure if it's necessary as a separate entry in here.
• 21:9, Anamorphic, XPan are either close to the other entries or so special, that I think it's better to being able to add them manually.

For the lighttable, I think then the aspect ratios should show the same names as the crop module, to keep it consistent. It can still display the correct ratio in brackets, just like the crop module does.

Furthermore, instead of showing aspect ratios smaller than 1, it should rather use the landscape orientation number and instead display "(portrait)" in bracket.

Alternatives

• Group the list by target medium, for example common aspect ratios for display (4:3, 16:9, 16:10, 3:2 etc) and paper sizes (4x5, 5x7, A4 etc).
• Add a dedicated filter only for portrait mode. Display 1.5 and 0.7 both as 3:2 and offer a filter for portrait and landscape mode.

Additional context

Start with the crop module presets and Lighttable Aspect Ratio filter described in the issue; no source files or tests are named. Compare their current labels, orientation display, and ratio-entry behavior against the proposed list. Done would require an agreed, consistent design covering both interfaces.