Seashore is fine once you’ve got used to its quirks (I stuck to the latest version: 0.5.1):
You don’t draw straight lines in it by holding the left button down and dragging the other end; instead, having selected the pencil tool, you hold down alt shift, left click once, then while still holding shift alt, move and left click elsewhere. For vertical, horizontal and 45º, it’s alt ctrl instead.
When you’ve cut or copied a piece of image from somewhere, and you paste into a Seashore image, it will appear in a gold-lined grid which you can drag, but you must click the Anchor button near the top right to fix it in place; just clicking away from that bit, as migrants from Microsoft’s Paint will want to do, won’t be enough.
The simple rectangular area selection tool can be made to select only squares by holding down the shift key as you press and drag. Without shift it’s supposed to default to ‘any rectangle’ but sometimes it defaults to squares even without holding the shift key down. If this happens, hold the alt key down instead and it will go back to non-square, and will default properly to non-square for a while.
If you’ve selected the entire image by clicking Command-a, then after you’ve done your copying and pasting into another window or whatever, you have to drag the box containing the gold-lined grid off slightly to one side, then left click on the area that’s left behind, otherwise you can’t get rid of the universal selection.
Similarly, when you’ve selected an area using the square lasso, and hit Command-c or Command-x, you should immediately click on the square selection tool on the extreme left and then click away from your selection area. Only then, do whatever pasting from the buffer you need to do.
And if you’re using that square lasso selection tool, when completing the boundary and clicking on the tiny circle that marks the completion, try to click on the bottom right of that tiny circle, since aiming for the dead centre doesn’t work so well. It might not respond quickly because it needs time to complete the completion. Or maybe you just missed the tiny circle 😦 .
That magic wand icon selects for similar colours in a connected lump. I found the Tolerance slider on the left useful, but got away without exploring the Intervals and Modifiers selectors to its right. Using the magic wand then selecting the inverse from the edit tab can be very useful.
When writing for Kindle, it’s useful to check that the areas in a colour diagram will still be distinct in “black and white” before you’ve finished the whole thing! Click the “selection” tab, then “color effect”, then “convert to grayscale”. Reverse of course with Command-z.
To create a new layer, not surprisingly, click New Layer from the Layer tab. Layers can be dragged above and below each other in the left-hand margin. Often, if edits don’t seem to be happening, it’s because you’re trying to operate in an unselected layer. It’s easy to get confused between “showing” and “selecting” a layer. (Click a layer to select, click the box to its left to show.)
When you create a new image in Seashore, its initial “background” layer is white, and selecting and deleting an area of this white background won’t do anything. New layers though are created transparent, and once coloured, cuts/deletions will cut transparent holes in them, shown by the grey chequer-board pattern. If you create a brand new and therefore transparent layer, and you want to write text into it, the pixels around the edges of the letters will be partly in the colour you’ve selected to write in, but partly in the colour of whatever can be seen below the transparent layer. Thus, if you want lettering eventually to appear in black on a red background, and you hope to do this by writing into a transparent layer followed by cutting and pasting elsewhere, make sure the original writing is done with red showing through, even if it’s from many layers below. If you do it with say white showing through, the edges of the letters will include shades of grey which will then look untidy when you later paste them into or over the red background somewhere else. A similar effect applies when drawing any antialiased edges of course.
If you want to close a multi-layered image file and preserve its final layers, the last format you save it in must be GIMP, otherwise the final version will be saved as a single combined layer (in the format of the last saved non-GIMP image). You might not be aware of this since while the window remains open, the layers can still be used even if you’re saving in a non-GIMP format. But the layers won’t be preserved in the non-GIMP files, even if you’ve been assiduously saving as you went along 😦 .
If you’ve produced a jpg in Seashore and want to reduce its quality to reduce its file size, save it quite big in Seashore first, close it, then open it again in Preview. Preview allows you to select the jpg file size on saving much more flexibly.
If you have a large very detailed jpg picture and you want to reduce it drastically, make sure to blur it in Preview first. (Select “adjust color” from the Preview Tools tab; other things can be adjusted there too. Slide the sharpness slider at the bottom to the left to blur.) Otherwise grey tone drawings on white come out like pepper sprinkled on white paper, and coloured photos look sparkly.
Seashore doesn’t like opening gif files, but it will save in gif format. If you have a gif file you want to edit, open it in Paintbrush and then save in for example tiff, which Seashore will open.
In Paintbrush, selecting areas and cutting and pasting them doesn’t work too well in zooms other than the one it opened in.