Quick Guide to Combine Image & Mosaic Layers

The Combine Image & Mosaic tool on the Special Functions main menu of ImagesPlus is used to build a composite image from one or more images. Each image is called a layer and the Combine Image & Mosaic tool maintains an image layer tree. The first image layer is the bottom element in the tree. Each new image layer is added on top of the previous image layer in the layer tree. A mask, blend mode, or opacity can be assigned to each image layer using the Combine Image & Mosaic tool. Image layer tree order is important since the composite image is built by combining each image layer with its mask, blend mode, and opacity from bottom to top tree layer.

Difference Between Process History Image Layers & Combine Image & Mosaic Image Layers
Combine Image & Mosaic Layer Rules

Combine Image & Mosaic Layer Examples

M42 Composite Image. Long 600 second exposure is used for the bottom layer. Short 60 second exposure with smoothed threshold mask used as top layer. First the long exposure is brightened with HDR arcsin or digital development to show the faint outer area. The short exposure is brightened with arcsin or digital development so that its core will fill the overexposed core of the long exposure with detail. After each modification to the image layers or mask the composite is rebuilt by pressing the Apply button on the Combine Image & Mosaic tool.

Apply a Filter With Mask. Initial image is set as the bottom layer. Duplicate of the initial image is set as the top layer. Smoothed threshold luminance mask is assigned to the top layer. Top image layer is sharpened. Composite image at lower center. All stretch, smoothing, sharpening, deconvolution, and color adjustment filters with optional blend mode, opacity, and mask can be applied in this way.

Blend H-alpha to Increase Detail and Preserve Color.First a Canon 20Da color image of the Rosette is aligned with a modified canon 400D H-alpha image of the Rosette using the Image Set Operations | Align TSR on Each option. The aligned 20Da image is assigned to the bottom layer with add blend mode to add its RGB color to the composite. The aligned 400D H-alpha image is assigned to the second image layer with lighten (max) blend mode to blend H-alpha with the red data of the 20Da image layer below. Both the 20Da RGB color image and 400D H-apha image are brightened using digital development and the composite rebuilt and checked. A luminace image is split from the 400D H-alpha image and assigned as the top layer with luminosity blend mode. The opacity of the top luminosity layer is adjusted to further blend the RGB and H-alpha data. A similar setup will blend an H-alpha frame with the red frame and luminace frame of an LRGB image set from a CCD.

Luminance Layering. Luminance layer on top with blend mode set to luminosity. Blue, green, and red layers have blend mode set to add. Composite image shown lower center has red, green, and blue added from the color components then the top layer is used as luminosity.

Building a Mosaic. First a two hour H-alpha exposure of NGC 7000 is aligned with a two hour H-alpha exposure of the Pelican nebula using the Image Set Operations | Align TSR tool with 3 star mosaic option. NGC 7000 is assigned to the bottom image layer and the Pelican Nebula is assigned to the top layer. Each layer is then brightened using digital development. The Pelican Nebula is brightened a little more than NGC 7000 to get it to match. Maximum combination is used on the Combine Image & Mosaic tool to build the composite image.

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