Digital Light & Color

If the Line and Arrow output image preview is set to side-by-side, scrolling the mouse on the Output half zooms it, scrolling the mouse on the Input half doesn't zoom it. Alt+scroll works on both.

Also the Line and Arrow Tool: is there a way to undo the last move (e.g. deleting a control point)?

With the Curved Line style, each control point determines the location, but also the curvature of the spline at this point. I don't seem to have much luck in drawing simple curves - i.e. Shift-click on the first control point, then keep clicking along the curve you want to draw - the default curvatures (tangents with two adjustable ends) seem weird and don't follow my intentions - have to keep 'uncurving' the tangents to make the curve running smoothly.

Last thing I'd like to report about this tool: it is possible to draw control points outside the input image boundaries. This may be ok, but somehow, I created a control point (unwillingly) that seems to be miles away from the image and I don't know how to remove it (as I can't find it) without deleting everything else that I've done in for the last half hour...

>> If the Line and Arrow output image preview is set to side-by-side, scrolling the mouse on the Output half zooms it, scrolling the mouse on the Input half doesn't zoom it. Alt+scroll works on both.

This is because the tool appropriates mouse events in the input image but not in the output image. Since it does not interfere with the output image, you can zoom and scroll without using Alt, while Alt is required to get control of the input image for scrolling and zooming.

>> Also the Line and Arrow Tool: is there a way to undo the last move (e.g. deleting a control point)?

You can delete a control point by Ctrl-Clicking near it.

>> With the Curved Line style, each control point determines the location, but also the curvature of the spline at this point. I don't seem to have much luck in drawing simple curves - i.e. Shift-click on the first control point, then keep clicking along the curve you want to draw - the default curvatures (tangents with two adjustable ends) seem weird and don't follow my intentions - have to keep 'uncurving' the tangents to make the curve running smoothly.

Unlike with some of the other tools where you constrain the curve by placing a large number of points, the intention in Line and Arrow is to use fewer control points and to control the shape of the curve between control points by adjusting the direction and lengths of the tangents.

>> Last thing I'd like to report about this tool: it is possible to draw control points outside the input image boundaries. This may be ok, but somehow, I created a control point (unwillingly) that seems to be miles away from the image and I don't know how to remove it (as I can't find it) without deleting everything else that I've done in for the last half hour...

I will look at limiting how far outside the image you can place a control point. Otherwise just try zooming way out until you can see the errant control point.

I'm getting those points 'far outside the image limits' almost regularly. I'm not sure what is causing it, but it looks like clicking too close to the existing point to add a point to a Curved Line may create those miles-away points...

Here is a little project with the intention to illustrate that one form of a knot can be easily transformed into another, and back (green and yellow arrows). I was thinking that it would be even more intuitive if the big 'transformation' arrows were not one green, one yellow, but have the yellow to green gradient (or vice versa). I can probably try to do it with a mask shaped as an arrow and the Composite with the appropriate gradient, but it sounds like a lot of work...

I was able to quickly make a mask for each arrow using the Flood Fill tool. Once you have the mask, the Linear Gradient transformation can create the gradient where the arrow was.
Here is the workspace script using the image from your post:

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workspace_script 1.0

PWP_Version ″Picture Window Pro 8.0.303″

original_script_pathname ″D:\Temp\Gradient.workspace″
associated_image_pathname ″″
associated_original_pathname ″″ -1
top_level_index 1

color_management enabled 1 on_mismatch 1 on_batch_mismatch 1 acs_profile ″sRGB Color Space Profile.icm″ gray_acs_profile ″Gamma 2.2.icm″ ar_profile ″AdobeRGB1998.icc″ gray_ar_profile ″Gamma 2.2.icm″ wcs_profile ″AdobeRGB1998.icc″ gray_wcs_profile ″Gamma 2.2.icm″ monitor_curves_file ″″ monitor_curves_enabled 0

image index 1 caption ″File Open - input.tif″ comment ″″ saved_as_pathname ″″ saved_on_date ″″ parent -1 bypass -1 same_size 0 size_specific 0 breakpoint 0 n_inputs 0 n_masks 0 command ‴file_open 0 n_files 1 current 0 from_default 0 multiple 0 prompt ″″ file1 ″D:\Temp\input.tif″ time1 ″20220715 002010″ selected1 1‴
end_image

image index 2 caption ″Linear Gradient″ comment ″″ saved_as_pathname ″″ saved_on_date ″″ parent 1 bypass 0 same_size 1 size_specific 0 breakpoint 0 n_inputs 0 n_masks 1 command ‴linear_gradient 0 style 2 operation 0 lx0 0.5073 ly0 0.6102 lx1 0.3630 ly1 0.5939 cycle 1 oversample 1 iscurve 0 isgray 0 is16bit 0 colorline 2 0.000000 5 4 3cfefe 1.000000 0 0 3cfc8e startcolor 0 endcolor ffffff exposure 4096 floatcurve 2 2 0.000000 0.000000 1.000000 1.000000 display 2 sync_scroll 1 auto_preview 1 amount 0 1 0 1 ″Amount: ″ ″Mask″‴
mask base_image 2 mask_number 0 base_input_index -1 initial_image -1 initial_mask_index -1 initial_level 0 caption ″Mask″ command ‴mask 0 nx 500 ny 337 mask_color 0 mask_transparency 2 mask_mode 0 mask16 0 mask_operation 0 initial_level 0 n_op 2 brush_settings 0 0 10 0 100 25 30 1 0 feather_settings 0 2 0 0 floodfill_settings 0 32 texture_settings 0 0 0 0 255 gradient_settings 0 2 0.000000 5 3 ffffff 1.000000 0 0 0 0 pinhole_settings 0 1 32 2 median_settings 0 1 1 blur_settings 0 50 curve_settings 0 2 2 0 0 255 255 0 shape_settings 0 2 2 0 0 255 255 separate_settings 0 0 0 1 0 1 0 1 0 0 ffffff 1 ffffff 1 ffffff 1 ffffff color_range_settings 0 0 ff 0 1024 0 1024 0 1024 0 1024 0 1024 0 1024 command1 operation 10 mask_mode 0 mask_operation 10 floodfill_x 0.4609 floodfill_y 0.6012 floodfill_threshold 32 command2 operation 5 mask_mode 0 mask_operation 5 feather_radius 2 feather_style 0 feather_corners 0 ‴
end_image

image index 3 caption ″Linear Gradient″ comment ″″ saved_as_pathname ″″ saved_on_date ″″ parent 2 bypass 0 same_size 1 size_specific 0 breakpoint 0 n_inputs 0 n_masks 1 command ‴linear_gradient 0 style 2 operation 0 lx0 0.5175 ly0 0.4744 lx1 0.3748 ly1 0.4663 cycle 1 oversample 1 iscurve 0 isgray 0 is16bit 0 colorline 2 0.000000 5 4 3cfefe 1.000000 0 0 3cfc8e startcolor 0 endcolor ffffff exposure 4096 floatcurve 2 2 0.000000 0.000000 1.000000 1.000000 display 2 sync_scroll 1 auto_preview 1 amount 0 1 0 1 ″Amount: ″ ″Mask″‴
mask base_image 3 mask_number 0 base_input_index -1 initial_image -1 initial_mask_index -1 initial_level 0 caption ″Mask″ command ‴mask 0 nx 500 ny 337 mask_color 0 mask_transparency 2 mask_mode 0 mask16 0 mask_operation 0 initial_level 0 n_op 2 brush_settings 0 0 10 0 100 25 30 1 0 feather_settings 0 1 0 0 floodfill_settings 0 95.5036 texture_settings 0 0 0 0 255 gradient_settings 0 2 0.000000 5 3 ffffff 1.000000 0 0 0 0 pinhole_settings 0 1 32 2 median_settings 0 1 1 blur_settings 0 50 curve_settings 0 2 2 0 0 255 255 0 shape_settings 0 2 2 0 0 255 255 separate_settings 0 0 0 1 0 1 0 1 0 0 ffffff 1 ffffff 1 ffffff 1 ffffff color_range_settings 0 0 ff 0 1024 0 1024 0 1024 0 1024 0 1024 0 1024 command1 operation 10 mask_mode 0 mask_operation 10 floodfill_x 0.4382 floodfill_y 0.4725 floodfill_threshold 95.5036 command2 operation 5 mask_mode 0 mask_operation 5 feather_radius 1 feather_style 0 feather_corners 0 ‴
end_image
current_image 1
end