Object Orientated Processing

Astronomical Imaging Conference November 10-12, 2006

By Adam Block

What Does Object Oriented Processing Mean?

• Salient features of objects (Stars, Nebulae, Galaxies… etc) can be identified early in processing data.

• Based on available processing tools, choices concerning how to emphasize (or de-emphasize) these features can be made.

• These choices affect the progression of processing steps for a given object.

A Tool Checklist• Deblooming (Acquisition)• Image Resampling• Deconvolution• Non-linear brightness mapping

(Curves, DDP)• Noise Reduction (smoothing)• Luminance Blending• Creation of Luminance from

RGB data• Using Filtered data as

Luminance (RRGB, Ha(L)RGB• Image Registration• Shadow/Highlights• Lighten Mode Blending

• Sigma Rejection• Gradient Removal• Multiplicative Contrast

Enhancement• Image Cleaning (clone/healing

brushes)• Minimum Filter• Layer Masking (Selective

Processing)• Color Replacement• Unsharp Masking• Image Scaling• Median (Pixel) Filtering• Star Shaping

General Goals

• Strive to achieve the largest range of brightness, color and detail for a given object.

• Processing choices should be incremental improvements that do not “reveal” themselves in the final image.

• Seek to minimize artifacts and biases in the data with each applied process.

Example Object Considerations

• Galaxy– Image Scaling, Deconvolution, DDP, Shadow/Highlights,

(Multiplicative Contrast Enhancement, High Pass Filtering)• Planetary Nebula

– Image Resample, Deconvolution, DDP, Star Shaping, Lighten Mode Blend

• Diffuse Nebula– Non-linear brightness adjustments (DDP, Gamma, Curves,

Shadow/Highlights), De-emphasis of stars (minimum/erosion filter), Multiplicative Contrast Enhancement, Noise Reduction (smoothing), Layer Masking

• Star Clusters– Color Control (Gamma, Curves), Deconvolution, (DDP),

Multiplicative Contrast Enhancement, Star Shaping

Star Shaping: Smudge Tool

�When pushing pixels, use less than half the inside of the brush (aperture) for best control�Push pixels from inside the star radially outward. “Over push” and bring back with a partial brush (as above) for smooth results. �Smudge linear features of a star (e.g. blooming artifacts) along the direction of the feature (first). Employ the above steps subsequently if necessary.�If darker values remain due to smudging sky values, use the dodge tool to correct. (Shadows and very small opacity settings)

Cleaning: The Healing Brush�This tool calculates replacement pixels based on values at the “from”and copy “to” locations. The blend attempts to produce a seamless result. �The latest version of Photoshop simplifies the application of this tool by not requiring a “from” location.�In all other earlier versions, choosing a “from” location, that is reasonably similar to the replacement location, gives the best results.�The healing brush is the perfect tool for cosmic ray and hot pixel removal. �Due to the behavior of the healing brush, use the regular clone tool near bright stars/objects. Also use the regular clone tool for crowded star fields where the separation of stars is equal to or less than the brush size.�Use the healing brush in combination with the smudge tool for difficult star shaping operations. The healing brush is especially useful in reconstructing gradients of brightness and color under the brush. (e.g. star halos)

Standard Calibration and Combine Sequence

1. Subtract Darks (Biases)2. Apply Flats3. Hot/Cold Pixel Removal4. Deblooming (if necessary)5. Save files in nested directory6. Register Luminance data7. Register Chrominance data8. Combine Luminance data using a rejection algorithm.

• Scale data if necessary• Resample data if necessary

9. Apply (Start) Deconvolution of Luminance data (optional)10. Combine Chrominance Channels (R,G,B) individually.

• Use rejection algorithm if there are enough files. • Resample to match Luminance data if necessary

11. Register Chrominance images to Luminance image. 12. Apply DDP to Luminance (Optional)13. Create Luminance TIF image for Photoshop.14. Create RGB TIF image for Photoshop

Star Clusters

• Resolution (in terms of small details like in galaxies or nebulae) is usually not a high priority.

• However, the “look” of resolution through non-linear brightness compression (showing the most stars possible at the same time) is generally main goal.

• Deconvolution and DDP can assist in both of the above. However, all sharpening processes make maintaining vivid star color more difficult (see next slide) – Only use Deconvolution on largely oversampled data.– Only use DDP on very crowded clusters with many overlapping profiles

• Brighten data in steps (using curves, gamma stretches, etc) to help keep the “feet” of stellar profiles. This will help provide a foundation to color stars.

Star Cluster Example Steps1. Standard Calibration2. Luminance

– Deconvolve if oversampled– DDP if overlapping stellar profiles

In Photoshop:1. Brighten Chrominance with Levels- do not let many stars become white clipped. 2. Brighten further with Shadow/Highlights and Curves.

• Adjust saturation a little if necessary.3. Brighten Luminance with Levels – do not let many stars become white clipped. 4. Brighten further with Curves.

• Add a point and make the top-end linear if necessary. (in order to brighten enough to see all the dim stars without clipping the core)

5. Blend Luminance and Chrominance data (using Luminosity blending mode)• If color is still diluted, change the opacity of the luminance layer by around 5-10% and

raise saturation a little. 6. If further brightening is needed, use Multiplicative contrast enhancement

process.7. Aggressively smooth (noise reduction) and de-saturate background.

Star Cluster ToolsMultiplicative Contrast Enhancement

1. Create Duplicate Layer of Image2. Brighten Bottom Layer Using Curves3. Select Top Layer and Use Multiply Blending Mode4. Adjust Opacity of Top Layer as Desired

Circular Gradient Mask1. Create Duplicate Layer of Image2. Add Layer Mask (Choose between Reveal All (White) and Hide All (Black).3. Create Circular Gradient (Gradient Tool). Size of circle is determined by the length of

the line drawn (with the beginning spot being the origin).4. Invert the Mask to apply effects to the central portion or outer portions of the cluster.

Star Shaping• Blur Central Portions of Bright Stars and Use Dodge Tool.• Use Minimum Filter on Stars to Shrink them (a little) and gain a greater foothold on

more color saturation. – Be very careful, Minimum Filter is not good on crowded star fields! (consider the combination of

the circular gradient mask above to control this and protect the core)

Multiplicative ContrastEnhancement

• This “trick” has an LLRGB behavior without the difficulty.• An image is duplicated as a second (bottom) layer. This

bottom layer is brightened through curves and multiplied by the top layer. Then the top layer is made slightly transparent to let the bottom (bright) layer come through.

• The multiplication forces anything zero-like to remain nearly zero while anything with a slight value is increased in brightness. (basically a contrast adjustment)

• The multiplication also enriches colors in a saturation-like behavior.

• Only use on images that have been thoroughly cleaned, noise-reduced and high S/N.

• Especially useful on galaxies with very dim out structures or nebulosity that fills the entire field.

Planetary Nebulae• White dwarf often plays “central

role” in the outcome of image. (Bluish color and star shaping)

• Choose to display image with G2V color balance or compensate for position of OIII line in filter set. (depends on particular nebula as to how important this is)

• For small high surface brightness objects, deconvolution through image brightness scaling and resampling is important.

Planetary Nebula Example Steps

• Acquisition Note– For small/high surface brightness PN with bright central star,

choose to acquire data unbinned through RGB filters.• Create luminance image from RGB data

• Standard Calibration• If Deconvolution and/or DDP is desired and there is a

small range of brightness levels in nebulosity- choose to scale ADUs to better fill available bit space. – Applied after the combine of the luminance image.

• If PN is very small, resample (perhaps double) image size before applying deconvolution to luminance image.– Apply after the combine of the luminance image.– Remember to resample the RGB data in exactly the same way.

• Do everything in your power not to white clip the central star so that its bluish color is retained.

Planetary Nebulae Tools

• Aggressive deconvolution can be applied to bright PN. – Using the Lighten mode blend this overly sharpened

image with the un-sharpened version to attain a PN with smoother nebulosity and detailed highlights. Use the Opacity setting to control the amount (or instead of Lighten, just use the Opacity of the layers to blend).

– Star Shaping• Smaller central stars give the appearance of a “professional”

high-resolution image.

– Apply contrasting Dodge and Burn to illuminated clouds for contrast effects.

Diffuse Nebulae (and Ha)

• If nebula is very diffuse and fills the field, do not deconvolve image.– It is difficult to isolate the background for noise

reduction/smoothing. Thus the sharpen is too great a cost in image quality.

• Seek to display the greatest range of colors and brightness available in the data. – Non-linear stretching through Curves and Shadow/Highlights is

the key.• Brighten in Levels to a point just before clipping. • Do not choose a black level until the end of the process. • Blend Ha into the Red channel AND the luminance

channel to roughly the same degree. This will ensure that all Ha in the luminance is colored red accordingly.

Diffuse Nebula Example Steps (Ha)• Standard Calibration• Blend Ha into R channel

– Scale Ha to equal R brightness.– Use Lighten (and Curves on Ha channel)

• Make Ha channel bottom layer– Flatten and call RBlend– Create RGB from RBlend,G,B

• Blend Ha in Luminance channel– Use Lighten and brighten overall image (especially Ha) to the

same degree shown in Rblend image. • Make Ha channel bottom layer

– Flatten and call LBlend• Create LBlend, RBlend, G, B image• Color Correct image

– Blend RGB (stars) into LRGB using Lighten• Make RGB bottom layer

– And/or Blend RGB image (top layer) using “Color Blend”• Layer Mask if necessary

Diffuse Nebulae Tools

• Selective color noise reduction– Color range tool

• Total combine of unfiltered and filtered data to create luminance image.– Also blending of Ha data if available.

• Shadow/Highlights on color layer for optimum range of represented colors.– Make certain correction factor is appropriate- typically

30-40%• Use original RGB data to maintain star color and

correct any color shifts

Galaxies• Detail is generally concentrated in small area(s)• Deconvolve only if S/N very high.

– Acquisition: No total integration time is too long. • Aggressive noise reduction/smoothing away from the galaxy. • Gradients tend to show up and be distracting.

– Make certain flatted images are valid.– Luckily large scale gradients do not generally impinge galaxies as

they usually take up a small part of the field.• Seek to display the greatest range of brightness, color, and

detail.– Avoid a “flat” galaxy. Make certain that after non-linear stretches that

brighter regions still appear more luminous than dim features. – Avoid over brightening chrominance layer. This will result in colorful

dim regions- but a loss of color in the brightest parts (nucleus).• Enhance prominent details through contrast processing.

– Only apply after image is completely “clean” and smooth.

Galaxy Example Steps• Standard Calibration

– Deconvolution and/or DDP of luminance layer tends to be the priority.

• Bring L and RGB into Photoshop– Brighten L with Levels and Curves (Levels before Curves)– Brighten RGB image with Levels, Shadow/Highlights, and then

Curves.

• Clean image and reduce noise/smooth.– Use Color Range tool to select everything that is real and invert the

selection. – Use a mask to help with noisy areas within the galaxy.

• Use High Pass Filtering with Overlay blend for dust lanes. • Use Multiplicative Contrast Enhancement for very dim

galactic halos.

Galaxy Example Tools

• DDP• Use High Pass Filtering with Overlay

blend for dust lanes. • Use Multiplicative Contrast Enhancement

for very dim galactic halos.