Image averaging to reduce colour noise in low light.
Much of the noise in a digital shot is random or nearly so. That means that in two images taken at the same time, the random noise will be different. So if a series of images are made, then added together and averaged, a great deal of the noise cancels out. The result is a shot which appears to have used a far lower ISO setting than was actually used.
If the shots are taken using the camera’s “native ISO” setting (usually 100 or 200 depending on model), so there is no amplificatation of the original signal before the conversion to digital, noise may be reduced to near zero.
Some mirrorless cameras can do this in camera, but the same thing can be done in post processing using any camera able to take multiple images. It’s a common technique in astro photography, where a lot of faint images are stacked and averaged to give one bright, but low noise image. Note- this only works for static subjects, though it can give interesting results with moving water.
Using Photoshop:- File, Scripts, Load files into stack. The file browser appears. Select the files you need, then tick both boxes for Attempt to auto align and Create smart object. Click OK. This part may take a few minutes, depending how many images and the speed of the computer.
Once the smartobject is created, you will see a single layer in the layers window. Go to Layer, Smart objects, Stack mode, and select Mean. This will produce an “averaged blend” image with reduced noise.
This method can also generate some fun composite images when significantly different files are used.
by Gordon Andrews
For all techniques open the file on your computer.
Select the Crop tool, make a selection over the image, then expand that selection beyond the borders of the image. When you click ok the background colour will be added as a border.
Go to Image, then Canvas size, add the amount of border you wish, then choose the colour, the dropper will select from the image as well as the palate.
To create a border around the entire picture, open the Select menu and choose Select All. To create a border around a certain section, use the Selection tool in the toolbar and select the area you want. Remember if you want to move your selection press the spacebar while holding down the left button of your mouse. From the Select menu, choose Modify and then Border. In the dialog box, choose the pixel size of your border. Locate the colour palette on the left-hand side of the screen. Click on the top square and select a border colour from the palette. (You can also alter this by using the refine edge in the Select menu.) Click OK, and then select Fill from the Edit menu. In the dialog box, choose the options to apply to the border. Finally deselect the selection (Ctrl +D) to leave the border.
To add a line, again select the position you want the line with the selection tool. Then go to the Edit menu, and select Stroke. Choose the width, the default colour will be the foreground colour, but if you click on it you can select another. Click ok, and then deselect to leave your line.
To add a textured border, first duplicate the background layer (Ctrl +J). Next make a selection, and create a background mask by clicking on the mask icon (rectangle with circle in it) at the bottom of the layers palate. Next select the background layer, and duplicate it again. Select this new layer and go to the Filters menu. Here, select an appropriate filter for your “Frame” e.g. texture then stained glass. Ok this and you should have your frame.
To add the border with the textured edge, see “Adding a sloppy border” in the photoshop tutorials of “The digital photography connection”- find it in the club website’s links.
To boost the colour depth in images, add a black and white layer to an image, and then simply change the blend mode of the B&W layer from normal, to soft light.
THRESHOLD LAYERS TO INCREASE CONTRAST IN PHOTOSHOP
by Andy Bennetts
Check that the cursor is set up properly. Edit>Preferences>Cursors – Other Cursors must be set to “Precise”
Make sure you can see the Info tab in the palette and also the Layers tab. We will use these later.
Open the image – it can be any type of file.
Select the Color Sampler Tool from the toolbar
Layer>New Adjustment Layer>Threshold. We are going to use the threshold layer to establish where the lightest and darkest parts of the image are.
There is no need to name the threshold layer – just accept the defaults. The color should be “None” and the Mode should be “Normal”. Click on OK.
The threshold histogram appears – the white triangle below the histogram can be slid right and left.
Slide the histogram triangle to the left until there is only a tiny amount of black visible. Click on OK.
Position the Color Sampler tool cursor over the black area and click – you are taking a sample of the darkest part of the image. This should leave a “target” on the black area, which will stay there.
Go to the layers palette and double click on the screen shape immediately to the right of the “eye” – this will bring up the histogram again.
This time, slide the histogram triangle to the right until there is only a tiny amount of white visible. Click on OK.
Position the Color Sampler tool cursor over the white area and click – you are taking a sample of the lightest part of the image.
With the two targets established, we don’t need the adjustment layer any more, so you can drag it to the bin to discard it. The original image will reappear, and this time the darkest & lightest parts of the image will be indicated.
Layer>New Adjustment Layer>Curves. We are going to use the curves layer to correct the colours for the two target areas. Accept the defaults & click on OK. The Curves histogram will appear.
Look at the Info panel. Towards the bottom, you will see two entries #1 and #2. These are the two samples, and beside the samples are the readings of Red, Green and Blue (RGB) we will deal with each colour separately.
In the curves histogram, click on the Channel drop down and select Red. For #1 and #2 we are going to set Red values of 10 and 245. You can do this on the histogram, by clicking and dragging the top and bottom of the straight line lying at 45 degrees on the graph.
Do exactly the same for the Green and Blue channel. When finished click on OK.
In the Layers palette switch off the “eye” in the curves layer to see the effect.
To get rid of the targets, click and drag off the image.
Save the file – flatten if you wish.
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