Use an opaque layer mask to show selected colour details against a grayscale background

Simple steps to using Layer Masks
Beginner level tutorial using Gimp 2.6

Do you have a coloured image that you would like to edit so that important objects will stand out from a distracting colourful background? If you have a picture that would have more impact if selected features were in full colour but the background was desaturated to black-and-white, this tutorial will show you one way to do that.


Open the image in the Gimp. 'Save as' and give it a new name; now the original image will remain unchanged, leaving you free to play without fear of destroying the original.

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Steps:
Create a duplicate layer. Layer > Duplicate layer
Desaturate the duplicate layer. Colours > Desaturate, click OK. Now the duplicate layer looks black, white and grey.
Create a layer mask between the two layers of the image. Layer > Mask > Add layer mask. A dialogue box appears. You want an opaque mask so select "White (full opacity)". Click Add.

The workspace will now look something like this:















Look at the Layers, Channels & Paths dialogue. The coloured bar that indicates which layer is presently active (the upper layer in this case) now includes a white square on the right-hand side of the thumbnail image. The presence of the square tells you that there is a layer mask, and the white colour indicates that it is an opaque mask.

In the Toolbox, check to make sure the foreground colour is black. Select the Paintbrush tool and choose a plain round brush. Make it fairly large. Set opacity to 100%.

Now brush over an area of the picture where you want colour to appear. Amazing - you are painting with black but because you are painting on the layer mask all the original colours appear where the brush has passed.

You can think of it like this - the opaque layer mask is like a sheet of white paper between two photographs (the layers of the image). Black paint has the magical ability to dissolve paper, not only the white paper of the mask, but also the paper directly above where black is applied. Black paint makes holes in the upper photograph and the white paper, allowing you to see through to the lower photograph.


Go ahead and paint over all the parts of the picture where you want colour to show through.

















If you accidentally 'colour outside the lines' you can easily fix things. Change the paint colour to white. Use the x key on the keyboard to toggle black/white as the foreground colour. Painting white over the mistake appears to remove the colour because you are painting on the mask and making the painted area white (opaque) again. To help you remember, think 'Black paint dissolves paper and White-out magically repairs it'.
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Further exploration:
If you want parts of the picture to show a little bit of colour, then you can paint on the layer mask with grey to allow a small amount of colour to show through. Darker shades of grey allow more colour, paler shades of grey are more opaque and allow less colour.

If you want a hint of background colour over the whole picture, adjust the opacity in the Layers dialogue. Opacity set at about 75% in the example gives a bit of colour in the background, looking less stark than the B&W version while still providing enough contrast to show the subject vividly.

Tip:
There is a keyboard shortcut so you can quickly increase or decrease the size of the paintbrush. Press and hold the ] key to scale up the size of the brush, and use the [ key to make it smaller.

Garden theme - Outer Space

My daughter said that she would sometime like to have a topiary tree clipped to look like a rocket on a launchpad. I think there is a skinny juniper called 'Skyrocket' but probably it wouldn't have enough foliage around the base to make proper fins, so if she wants a realistic looking rocket topiary she might have to make a wire frame.

We thought there would need to be some other space-theme elements in the garden so the rocket wouldn't look out of place, and we amused ourselves furnishing an imaginary Space Garden.

It needs a flying saucer - this could be a metallic birdbath or fountain on a slender pedestal, with a ring of LED lights around the rim.

The flying saucer needs surroundings that suggest alien worlds. What about a ground cover of black mondo grass with Allium cristophii (ornamental onion) floating star-studded globes above the black plain? Or a gravel garden planted with 'Living stones' (lithops)?
And cactuses - they often look like aliens. Elephant's Foot also looks suitably intergalactic.



(Photo shows an alien family slightly bemused by the Earth garden they are visiting.)
















Ornaments are practically mandatory. Anything is possible, from an orrery to a garden gnome in a space suit. An Aeolian harp to play the music of the spheres... A fountain with a ringed planet made of glass spinning on a swirl of water...

What plants could we include? Sunflowers, of course... maybe decorated with stick-on eyes, ears and antennae so they look like extra-solar tourists. Moonflower vine. Star jasmine. Lunaria, for its moon-shaped pods. Cosmos. Aster. Rocket. Jupiter's beard. We would love to include Venus's fly trap, not only because of its name but also because it looks so spacy, but it wouldn't survive in the open garden. Maybe the garden can feature a special habitat, an interplanetary Wardian case, to accommodate Venusian visitors.

It was fun to play with a few ideas for a space-themed garden. If anyone has actually made one, or would like to add to the lists of plants or ornaments, the Impatient Beginner would like to hear from you.

Daffodils and Gazania ground cover

Well, we didn't win Tattslotto so it looks as if we will have to do without our two-storey garage/greenhouse.

In any case, there will be changes in the garden. The big windstorm reminded me of the danger of the gum tree near the house. The tree will have to be removed - with regret, because the birds and possums will miss it.

In the space vacated by the gum tree I intend to plant two or three wattles of a sort that do not grow tall ... Acacia podalyrifolia if I can get it in Tasmania. I love its round silvery leaves.

While digging an extension to the bulb garden I discovered an old concrete footpath buried under a layer of three inches of topsoil. No wonder the grass never grew well there! I'm not up to the job of removing the concrete (as the previous owners weren't) and more topsoil is not an option, so I am thinking of other choices. I would prefer a ground cover plant so I want to try Gazania rigens var. leucolaena over the buried concrete.

This gazania is tough and drought tolerant. I hope it will be able to cover that difficult spot where grass can't grow. If it is successful, then I will extend the area that it covers into the bulb garden. In time it can form a silvery carpet out of which the naturalised daffodils, narcissus, freesia, white nerine and zephyranthes appear in their season.

I bought a bag of twenty daffodil bulbs to start the new extension to the bulb garden. They are simply described as "yellow" so I expect they are the typical golden-trumpeted daffodil. Today I will finish digging the ground, plant the daffs and add some cuttings of the silver leafed gazania. I'm looking forward to spring.

Wish list - Greenhouse on top of Garage

We have an old fibro-cement garage. The walls are cracked, the roof is a rusted ruin, the floor is uneven. It needs to be replaced and my husband has been looking at prepack steel sheds to see whether one of them be a suitable replacement.

I would love to have a greenhouse, especially one with electricity and water connected. If I had a greenhouse you would always know where to find me! Alas, our suburban block is too small to have both a greenhouse and a garage. Dear Husband is correct in saying we need a garage, and it makes sense to build a slightly bigger garage than the existing one so he will have space for his woodworking tools. It makes sense, all right... but I wish...

I had a flash of inspiration. Could we put a greenhouse on top of the garage? Have a two-storey combined garage/workshop/greenhouse? I loved the idea immediately. Imagine it - a possum-proof vegetable garden - a warm sheltered spot for the hydroponic tomatoes and cannas - electricity for the hydroponic pumps - a safe pond space for Katherine's fish. In my imagination I have already begun to design it. The staircase annexe can incorporate a water tank to store rain runoff from the roof. There can be solar panels along the north-facing knee wall.

Obviously such a building would cost considerably more than a simple steel shed. There's the rub. Our pension income is limited (particularly worrying now that financial institutions seem a bit tottery) so we won't be able to afford it unless we win Lotto. I am on my way to buy a ticket now!

Tropicanna in black urn

Part of my hydroculture experiments, the canna is growing in scoria medium. It is growing well, though it seems to be smaller than similar types that I have seen growing in soil. However, they may simply be older plants.

Next year I think I will add some of those mahogany coloured nasturtiums. They should do well in the same conditions as the canna and the colours will complement each other.

Originally I had intended to paint the urn with very fine marbled veins in olive, charcoal and light coral - similar colours to those in the canna leaves. Now I think it looks better simply in black.





Here is a close up of the canna's beautiful leaves.

Rough plan for small pot-in-pot planter made from plastic milk bottle

Use post-consumer plastic bottles for this project! We get milk in 3 litre bottles with handles as in the attached sketch and I think 3 litres will be a suitable size for a basic stacking unit of the "strawberry tower".

Cut an access hole near the top of the milk bottle. This hole must be big enough for a small plant pot to be put inside the milk bottle. Cut a drainage hole near the bottom of the bottle, about 2 cm above the bottom.

The water reservoir will hold about 500 ml. A tube made of synthetic fabric (spunbonded polypropelene or polyester - think geotextile, agricultural fleece, or nonfusible nonwoven interfacing) will connect the water reservoir to the plant pot. Right now I am thinking I will make a tube of synthetic fabric about 5 to 7 cm high and 2 cm in diameter and fill it with sand to act as a capillary tube to wick water up to the plant but I have not tested this yet.

A "floor" is needed to separate the water reservoir from the upper chamber of the bottle. Cut a margarine container down to about 2.5 cm in height, cut several drainage holes (about 1 to 2 cm in diameter) in its bottom and invert it --bottoms up!-- in the base of the milk bottle. The margarine container will not fit perfectly but it should be large enough to hold the actual "floor". Cut the "floor" to fit the milk bottle cross section. Use a disposable plastic plate or similar material to make the "floor". Remember drainage holes. We are trying to make a "floor" sufficiently strong and stable to support the sand/coir and the plant in its pot. Do not insert the "floor" in its final position just yet.

The capillary tube will have to pass through the "floor". Cut a 2 cm hole near the centre of the "floor" and thread the tube through the hole so the "floor" is at the approximate mid-point of the tube's length. Now the "floor" can be put in position on the margarine tub. The capillary tube should reach to the bottom of the water reservoir.

Now put about a 2 or 2.5 cm layer of the sand / coir mix on top of the "floor". The capillary tube should not be buried. Make sure that the end of the tube extends out of the sand mix distinctly. The plant pot will have to be centred on the tube, and good contact will have to be made between the tube and the potting soil in the plant pot.

Now take the plant pot that will be put inside the milk bottle chamber. Cut several 1 cm drainage holes in its base, and in the centre of the base cut one 2 cm diameter hole (or whatever diameter the capillary tube ended up as). Insert the plant pot into the milk bottle and make sure that the capillary tube reaches through into the plant pot. Fill the pot with potting mix and plant the seedling and water in.


Use the overflow hole to fill the water reservoir. Occasionally it may be necessary to add water from the top - because constant bottom-watering may cause salts to build up on the surface of the potting mix - but generally watering will be done via the water reservoir. Evaporative loss should be fairly small. It would be interesting to see whether the relative humidity inside the shell formed by the milk bottle is very different from the humidity outside, but I don't have a good way to quantify it. The test of this growing system will simply be whether the plants thrive, and I hope they will.

Now for something completely different. I expect my new flush cutters to arrive tomorrow so I am likely to get obsessed with wire work for a while. This is probably the last post on Gardening for at least two or three weeks.

Musing on the under-pot zone

Have you noticed how potted plants try hard to get their roots out of the container? Potted pelargoniums, marguerite daisies and cordylines dawdle along until they get their roots into the soil underneath the pot and then they put on a spectacular flourish.

What causes this? It can't simply be that their blueprints tell them to grow their roots to a certain defined extent, because roots try to escape from very large pots as well as small ones. They must be looking for greener pastures. Perhaps the soil under the pot is cooler and moister than that inside the pot, or perhaps there are better combinations of water and air in the under-pot zone.

I am thinking about this in designing the strawberry towers mentioned in an earlier post. I would like the plants to be as happy as possible in their hanging containers while at the same time I would like them to be low maintenance and only require watering and turning every two or three days.

So I am thinking about ways to simulate the under-pot conditions that plants seem to like and ways to create these conditions in the hanging containers. My earlier designs for the hanging containers included a water reservoir (like the pop bottle planters or a self-watering pot) but now I am inclined to try a base that is filled with coarse sand (like a miniature capillary watering tray) with a top unit containing potting mix set on top of the sand. Plant roots should be encouraged to spread from the top unit into the sand-filled base.

Experiments are needed to establish whether plant growth would be better in this type of system than in the simple water well pots, and to establish whether plants would prefer the top unit to be set into the sand or suspended slightly above it, and whether sub-irrigation or top watering would be best, and whether fertiliser pellets would be better placed in the top unit or in the sand... There are lots of possibilities to try. I looked on the internet to see if anyone has done any of these experiments already. Pot-in-pot growing looked similar but I didn't find enough published information to answer my questions. I will have to find out the slow way.

Summer will officially be finished in two weeks so I had better get busy.