Author: Joshua Akin – Digital Imaging Officer, Royal Museums Greenwich
An insight into our workflow for cutting out images of complex, rigged ship models. This involves using masking techniques so that we can ensure that the models appear on a pure white background.
In 2006, we undertook a ship model photography project, which took over 6 years to complete. We photographed over 2500 ship models, ranging from small craft, fishing and hunting vessels to powered warships just to name a few.
The project served the following criteria:
- To refine and update the catalogue of the collection.
- Provide access to collections via collection’s online.
- Most of the collection was moving to Chatham for storage.
The ship models had to be photographed at Kidbrooke outstation store, as they could not be moved to the photographic studio. The equipment we used off-site at Kidbrooke were:
- Hasselblad H3D II-39
- 105mm (macro) lens
- 80mm lens
- 50mm lens
- Tilt-shift adapter
- Xrite colour checker
- Broncolor flash heads and soft boxes
- Mac Computer and Eizo monitor workstation.
Ship models sizes ranged from 2 centimetres to 4 metres.
Photography was broken down to shoot the models in order of size: small, medium and large.
Some of the bigger models could not be shot in the allocated area, so a purpose built container was used to carry the ship models out of the building and into the large foyer.
All ship models were shot on a white or black background. Three photographic views were captured of each ship model:
- Bow ¾
- Stern ¼
In some cases the curator requested up to 10 views of a ship model, as it was deemed necessary due to historical importance.
Due to the quality of the Hasselblad H3 cameras, curators were able to see the detail inside the models that was not easily seen with the naked eye.
- Cut out ship model to a clean white background.
- Remove shadows.
- Keep every detail of the ship model.
Most of the masks that we create with channels end up needing that extra nudge and fine tuning.
The ship model is dark grey, not pure black, and they have little white holes in them. The white areas have a fine haze of light gray sprinkled here and there.
The mask’s edge can be too tight, too loose, too sharp or too soft.
The diagram represents the relationship between grayscale values in alpha channels, mask opacity, and selections.
Using the image editing capabilities in Photoshop, we worked on the alpha channel directly to perfect the mask.
The alpha channel is then inverted, so white reveals and the black area hides.
The alpha channel is loaded as a selection to isolate the ship model.
Workflow to make a black and white mask using:
- Dodge and Burn
- Curve Tool
- Pen Tool
Duplicate layer and change blending mode to multiply to darken ship model image.
Choose the best channel from the colour image that has the best near black and white contrast. Make a copy of the blue channel.
Change multiply blending mode to normal.
Open up the Levels tool and slide in the black to make your object black, without clamping the white areas.
Duplication the blue channel twice and name the first one HIGHLIGHT. With the second blue channel name it SHADOWS and invert it, so it is a negative.
Go to Image / calculations and select HIGHLIGHT alpha channel as your first source and SHADOWS as your second source and check mark invert. Then change blending mode to multiply or Linear Burn and adjust opacity, to get an almost black object. Save it as a new Channel.
Use the burn tool to target shadows and set exposure to a reasonable exposure between 2-10%.
Start burn in the light rigging areas by gradual strokes until it is black.
Open the Curve Tool and sample the gray background colour with the eye dropper tool, notice the ball along the curve line. Select the pencil tool to draw a line horizontal line across the upper right, changing all the tones of the gray to pure white, the press the smooth button twice, to smooth out the light and dark values. If it is not 255, kept apply the same technique until it is using the info dialog box.
Use the Dodge burn to dodge the darken gray areas around the object caused by the burn tool. Use Highlights and 5-10% exposure.
Use the Pen tool for straight edges, such as the base of the ship and also removing unwanted elements in the background.
Load the path selection and fill the alpha channel with white.
Making the RGB channel visible, enables you to view the edge of the mask in Quick Mask mode. Once you are happy refining the mask, turn of the RGB visible channel.
Load the selection from Mask channel and make a duplicate layer of the background. Make an adjustment layer mask of that selection.
Make as solid colour layer adjustment just before the duplicate layer and choose 255 white.
Use the blur tool to simulate the depth of field effect in the areas that should be blurred.