work flow of image processing

8/10/2019 work flow of Image Processing

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Image processing is a method to convert an image into digital form and perform someoperations on it, in order to get an enhanced image or to extract some useful information from it.It is a type of signal dispensation in which input is image, like video frame or photograph andoutput may be image or characteristics associated with that image. Usually Image Processing system includes treating images as two dimensional signals while applying already set signal

processing methods to them.

It is among rapidly growing technologies today, with its applications in various aspects of a business. Image Processing forms core research area within engineering and computer sciencedisciplines too.I mage processin g basically inclu des the foll owin g thr ee steps .

Importing the image with optical scanner or by digital photography. Analyzing and manipulating the image which includes data compression and image

enhancement and spotting patterns that are not to human eyes like satellite photographs. Output is the last stage in which result can be altered image or report that is based on image

analysis.

Purpose of Image processing:

The purpose of image processing is divided into 5 groups. They are:1. Visualization - Observe the objects that are not visible.2. Image sharpening and restoration - To create a better image.3. Image retrieval - Seek for the image of intetrest.4. Measurement of pattern Measures various objects in an image.5. Image Recognition Distinguish the objects in an image.TypesThe two types of methods used for Image Processing are Analog and Digital ImageProcessing. Analog or visual techniques of image processing can be used for the hard copies like

printouts and photographs. Image analysts use various fundamentals of interpretation while usingthese visual techniques. The image processing is not just confined to area that has to be studied

but on knowledge of analyst. Association is another important tool in image processing throughvisual techniques. So analysts apply a combination of personal knowledge and collateral data toimage processing.

Digital Processing techniques help in manipulation of the digital images by using computers. Asraw data from imaging sensors from satellite platform contains deficiencies. To get over such

flaws and to get originality of information, it has to undergo various phases of processing. Thethree general phases that all types of data have to undergo while using digital technique are Pre-

processing, enhancement and display, information extraction.


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Image acquisition:


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digital camera: for fine art prints save your images in RAW mode through the software with thecamera or a third party program such as Breeze Browser (for Canon) or Bibble (Nikon) andconvert to 16-bit TIFF. Use JPEG (which is a lossey compression) only for the web or e-mail.

Scanner: scan at the highest resolution (e.g. 4000 pp/i; 48-bit) and at the highest filmdensity the scanner can capture; do not alter image with scanner unless you have superiorsoftware (e.g., Silverfast , Vuescan); use Digital ICE (if available) when working with a

particularly dirty print. Save as a TIFF file to your "Image Capture" directory. Open the image in Photoshop and convert to your working space (e.g. Adobe RGB

1998). Rotate image to vertical if needed (Image>Rotate Canvas). Adjust minor rotational error of horizon or verticals: choose measurement tool (under the

eyedropper fly-out menu or Shift + I until the ruler appears); draw desired vertical orhorizontal line on image; open Image>Rotate>Arbitrary>OK.

Histogram: review histogram (Image>Histogram) to see if it is reflective of the imagewithout excessive highlight or shadow clipping; if graph is excessively bunched right orleft, rescan unless this is a high-key (light tone) or low-key image.

Run curser over histogram and note ranges of excessive concentration of pixels for eachchannel.

This hi stogram clearly shows work to be done

Crop & Clean:


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Double click on same icon in Threshold layer; move slider right; OK; click colorsample eyedropper on black point Sample #2; delete Threshold layer (click/drag toashcan).

Click Color Sample tool on a true gray of any tone for Sample#3; click on thedominant color for sample #4.

Note: You are now able to monitor these points throughout the remaining corrections.

6. Set Print Map Target Preference

Note: if the destination is print, change the white and black points to match mediacharacteristics so that you hold some information in white and black. The following arevalues for sheet-fed press on coated paper or Lightjet 5000, and most Epson printers.

6.1. If Levels is not open, Image>Adjust>Levels. 6.2. Double click Set White Point highlight eyedropper (right); set the B (in

HSB) to 95% (RGB values for 242,242,242); click OK: (if working in CMYK use5,3,3,0).

6.3. Double click shadow eyedropper (left); set B to 5% (RGB to 12,12,12);OK: (CMYK, 65,53,51,95).

Set White Point

Note: Our next step in color correction is to adjust the histogram with Levels. Some photographers use iCorrect for steps 6-11. For more precise control follow theWorkflow. Well use the eyedropper to remap the white and black tones.

While still in Levels check for true white : open Blue channel; move highlight

slider left to end of histogram; if input level stops short of 244, there may be no truewhite so eyedropper may not be used (skip step); if values are over 244 or to createtrue white, click Set White Point eyedropper (right most).

Run eyedropper over area of neutral white identified (do not use specular highlight,reflection, glare, etc., which have no detail or image will be flat); zoom in ifnecessary (Ctrl-plus) reading Info palette to find brightest point where you want sometexture (hold down space bar to move image).

7.3. Hold down shift to move Sample #1 if necessary; set pointer over sample targetand click to set white point.

7.4. Toggle Preview for results; hold down Alt to toggle Cancel toReset to undo

Set Black Point Check for true black ; open blue channel; move shadow slider right to beginning of graph; if histogram stops short of 8, there is no true black so eyedroppercannot be used (skip step); if values under 8, click Set Black Point eyedropper (leftmost).

8.2. Run eyedropper over area of neutral black (with some detail) to find optimum point; zoom in if necessary (Ctrl-plus) (hold down space bar to move image).


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8.3. Hold down shift to move Sample #2 if necessary; set pointer over sample targetand click to set black point.

No True White or Black If no true white, open each channel (red, green, blue) separately and move each

highlight slider until its just within the graph (to create some white); do not movecenter slider. If no true black, open each channel (red, green, blue) separately and move each

shadow slider until its just within the graph (to create some black); do not movecenter slider.

EXPAND DYNAMIC RANGE

Note: If after the previous steps your histogram still does not extend to the left and rightends, you may want to remap it to use the full dynamic range. Be careful, however, withhigh key or low-key images.

Expand Histogram Range If Levels is not open, then (Image>Adjust>Levels) (or Levels>Adjustment Layer>Levels

in 8-bit); move the left then the right sliders to where they just meet the histogram.

COLOR BALANCE

Note: Colorcasts will occur when the ambient light is a different temperature than the film. Filters can help, but often an imbalance remains. The new (PS7) Auto Color can betried, but it seems to create as many color casts as it cures.

11. Remove Colorcasts in Shadows and Highlights

If monitor samples are not already established, set as above. If white point pixel values are the same in sample #1, there is no color cast;

otherwise, choose lowest value channel (e.g. Green). Move Set White Point slider to left until value in Color Sampler Info matches highest

value (e.g. Red); do the same for remaining (e.g. Blue) channel. Check sample #2; drag Set Black Point slider right to match lowest value in sample

#2 in Info palette. Click OK; open Layers palette; click on eye in Levels layer to check result.

12. Remove Colorcasts in Gray Midtones with Curves

Note: If a colorcast is clearly visible in neutral midtones, this technique is preferred tousing the gray eyedropper (which sets the R, G and B of the point to the same values) since you can see results of the adjustments.

If you have not yet done so, add a third Color Sample #3 by shift-clicking in a truegray area of any tone; note the channel with middle value.


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Open Curves (Image>Adjust>Curves), then open, e.g., Blue in channel popup, click onmidpoint and move up or down (use up/down arrows) until value in the Info palettematches middle value, e.g. Red.

Do the same with e.g. Green channel so all three channels are equal.

13. Precise Color Adjustment Note: In the event the above does not work, to selectively enhance a specific colochannel or range of colors, Curves provides a more flexible control than Levels.

While still in Curves dialog Alt-click within graph to change to 10x10 grid. Go to channel of color to modify, Red (cyan), Green (magenta), or Blue (yellow). Click on each of nine intersections of graph to anchor curve. Run eyedropper over position in image of target color with the mouse button down; Ctrl +

click to add a handle. Remove the lock down points adjacent to handle by dragging them off graph.

Drag point up and left (carefully) to add red, green, or blue, and down right to add cyan,magenta or yellow; (hold down Alt and click Reset to clear). Save if in an adjustment layer (to reapply if necessary later), then OK.

Individual colors can be tweaked with Curves.

ADJUST CONTRAST AND SATURATION


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14. Contrast Adjustment

With Curves still open, Alt-click within graph to change to 4x4 grid. Ctrl + click on area to be lightened; Ctrl + click on an area which should be darkened

setting two handles.

Move upper handle up and left and lower down and right to produce s-curve. Ctrl + click on brightest area; reduce contrast if Output is over 244; Ctrl + click black;reduce contrast if Output is under 12.

o Alternatively: Click on three intersections to lock down curve. Click on lower anchor and move down with down arrow; click on upper anchor and

move up with up arrow to create smooth s-curve (reverse to reduce contrast); monitorresults in Info palette to avoid pure black or white as above; OK.

Cur ves gives greater control than Br ightness/Contrast.

15. Increase Saturation

Note: Since faster films and most scanners reduce saturation, you usually have torestore some color depth. However, be careful not to overdo this since over saturationmay look flashy at first, but does not wear well.

Open Image>Adjust>Hue/Saturation.

Select Master to change overall saturation (+10 to +20 usually enough); (inkjet printers require more saturation than Lightjets).


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To correct saturation in a specific color range, go to channel to modify (R, G, or B),select a color with the eyedropper, adjust the default with + or eyedropper, ormove color sliders.

Use Lightness not at all or only for minor adjustments. Toggle Preview to assure saturation is not overdone; click OK.

EDGE SHARPEN AND CLEANUP

Note: If your edges look sharp and clean or you have pre-sharpened in the scanner (with perhaps Nikon software set at 20,10,3), skip this step. This is the first of a two-pass sharpening; at this time moderately sharpen edges only. If you are in 16-bit, sharpeningis less destructive in Lab mode L channel since it creates no color shifts. Dontconvert to Lab if in 8-bit.

16. Edge Sharpen in Lab L Channel

Check setting: Edit>Color Settings>Advanced Mode checked>ConversionOptions>Dither Off.

Change Master to Lab mode (Image>Mode>Lab Color), the sharpening space of choice. Make second duplicate of original (Image>Duplicate), name Edge Mask; change

Duplicate to 8 bit (Image>Mode>8 Bits).o Note: Pick up from here in 8-bit.

Make color channel with highest contrast active, e.g. Red; isolate edges withFilters>Stylize>Find Edges.

Invert image with Image>Adjust>Invert (or Ctrl+I).

Delineate edges with Filter>Noise>Median with radius value of 2. Thicken edges (Filter>Other>Maximum) with 4 as radius. Smooth edges with Filter>Blur>Gaussian Blur, radius 4. Increase contrast to point below which artifacts are picked up

(Image>Adjust>Brightness/Contrast). 16.10. Create selection (marching ants) outline by Ctrl + click the red channel in the

Channels palette. Choose Select>Save Selection and name Edge Mask . Make the 16-bit Master active by clicking on it; open Lightness channel in Channels

palette by clicking on it; open View>New View; zoom in on detail with zoom tool oneither view so you can see detail as well as overall effect.

Load edge mask (Selection>Load Selection>Edge Mask). Eliminate marching ants outline with Ctrl+H. Choose Filter>Sharpen>Unsharp Mask; set amount to 100-150, radius at 1.0-1.5,

threshold at 0-1; adjust as necessary for moderate edge sharpening, with amount as finalchoice.

Ctrl + H to return selection outline; Select>Deselect to clear edge mask (make sure maskis cleared or it could affect subsequent steps).


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SAVE AND CONVERT

17. Save and Convert to 8-bit

When done with overall corrections, save file to Hi Res Images directory inPSD format.

Note: image should be very close to optimum at this point. Gamma and brightnesshave been corrected, white and black points established; color casts eliminated withwhite, black and gray points set to neutral, saturation level adjusted, and edges sharpened. Area corrections, resampling, and final sharpening remain.

Convert to 8-bit (Image>Mode>8 Bits). Save 8- bit version using a different name, e.g. save as Master in Master

Images directory.

Note: image is now in 8-bit mode, so all selection tools can be used (Magnetic Lasso Paintbrush, Eraser, Color Range, etc. are not available in 16-bit). Adjustments of thiskind are best done in layers (not available in 16-bit mode) so they can be edited at alater time.

SELECTIVE CONTRAST AND EXPOSURE CORRECTION

18. Blending Modes for Tone and Contrast

Note: In the event further minor adjustment is needed, Blending is a method of correctingtone or contrast of images without the problems of selection techniques. However, formore precise control use the selection techniques below. The key Blending modes are:

Multiply-increase density of entire image if underexposed (better than Darken mode).

Screen-lightens image

Soft Light, Overlay, Hard Light- increase contrast progressively

Luminosity-selects light areas only

Make duplicate to monitor effect; return to original. Add Layer>New Adjustment Layer>Levels; click OK without adjustment.. In Layers palette, move Opacity to 0%; open Blending mode in drop-down menu and

raise Opacity slowly. Open a new layer (Layer>Duplicate Layer); switch to Luminosity mode (preserves hue

and saturation of base) in Layers palette (or Ctrl + Alt + ~)..


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Click on Red, Green, and Blue channels to see which shows best detail in area to beadjusted (red for skies, green for faces); return to RGB.

Name Layer, e.g. Red Only ; leave new layer active. Choose Image>Apply Image; set Layer=Merged; Channel=Red; Blending=Darken for

skies, Normal for faces, Soft Light to increase contrast; set opacity at 100%

(experiment with this); toggle Preview. Choose Layer>Merge Down.

19. Selecting a Specific Area for Correction

Note: Some images require selective adjustment. Identify an area that needs furthertweaking, e.g. sky, foreground, and determine optimum method of creating a selection Precision is not necessary since selection will become an editable mask. Note: it is sometimes easier to select solid color areas and then Select>Invert.

To select a solid or almost solid color skip to Color Range (best way) or use

convenient Magic Wand (options bar set to tolerance of 8-16 depending on colorvariation, anti-aliased on, contiguous off); Shift + click to add to selection, Alt + clickto remove).

For areas with well-defined edges use the Magnetic Lasso tool (feather off, width 10,contrast 10%, frequency 50); hold down Alt to convert to freeform Lasso where edgesare ill-defined; double click to close loop; Alt-Z to undo.

For entirely freeform selection use Lasso tool. (Marquee and Pen tools are notgenerally useful for photographs).

Choose Select>Feather and enter 1 or 2, or up to 6 radius for edge blend of hi-resimages.

20. Color Range Selection Note: Color Range is more precise than Magic Wand and generates a preview of themask. You may want to use Color Range after making a selection to limit area of mask.

Double click on Quick Mask; click on color box and set for contrasting color; opacity50%; click on standard mask (Q).

Choose Select>Color Range; select option from dropdown list, e.g. Sampled Colors;fuzziness 0.

Switch between image and mask by clicking Selection or Image radio buttons or byholding down Ctrl key.

Use eyedropper to specify color to be adjusted; + eyedropper (or Shift-click)to add (or drag); "-" eyedropper to delete; Ctrl-Z to undo.

Click on Invert to mask color. Hold down Ctrl key to toggle preview. To enlarge selection, use Select>Grow, or Select>Modify>Smooth Set. Select>Inverse to reverse selection if required.


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Using ColorRange to select background is often easier than selecting the object. The backgroundcan now be lightened for separation, and with Select>Inverse, only the duck sharpened.

21. Creating and Editing Mask

Note: Generally selections must be edited regardless of the selection technique. Quickmask is the most efficient editing tool of standard selections.

Click Quickmask mode in Tools palette (or hit Q); press D to set foreground color toBlack.

Double click Quick Mask channel and set to 50% luminosity and radio click maskedor selected area. Select a paintbrush (press B); paint with black in foreground to add to rubylith overlay,

paint with white (press X) to erase color. Use the Gradient tool (press G) to draw a gradual transition. Switch back to normal mode (marching ants) (Q again to toggle); Select>Feather 2-3

or 4-6 for hi-res. Select>Save Selection; goes into alpha channel and may be saved for reload (select

Load>Selection>Alpha).

22. Adjusting Selected Area

Note: Now that you have your selection, you may work on it with a variety of tools.

For the most control, Layer>New Adjustment Layer>Levels/Curves/Saturation tocorrect selection.

23. High-bit Mode Selection


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Note: most selection tools are not available in 16-bit mode; selective corrections areusually done in 8-bit adjustment layers, but the following will guide you in 16-bit selection for those who want to continue in hi-res for whatever reason.

Open duplicate (Image>Duplicate); name 8 - bit mask ; choose Image>Mode>8

Bit. Follow steps above for creating a mask. Save selection (Select>Save Selection) and name, e.g. trees ; click OK. Click on the 16- bit original and Select>Load Selection trees ; delete the 8-

bit image. Use Image>Adjust>Levels/Curves/Saturation to correct selection.

24. Rescuing Shadow Detail

Note: if shadow details remain repressed after all of the above, the following may behelpful.

Open Color Sampler Tool; move sample #4 (click-drag) to shadow area near detail tomonitor shadow.

Open Image>Adjust>Levels; move middle slider left until details appear in shadows but color sampler does not show degradation of shadow (ignore rest of image).

Make a copy for reference (Image>Duplicate); make original active. Window>Show History; click on left box in History channel to set history brush (icon

will appear); activate previous state; use history brush (press Y) choose soft brush, seton Lighten, 50-100%, to paint in shadow details using duplicate for reference; closeduplicate.

25. Graduated Neutral Density Filter Note: If you wish you had used a GND filter when you took the picture, this step mighhelp.

Make duplicate (Image>Duplicate); name GND ; make duplicate layer(Layer>Duplicate Layer), name, e.g. Sky .

Use Levels or Curves to adjust exposure (brightness/contrast) of sky without regardfor the rest of the image.

Click Quick Mask icon at bottom of Layers palette; click on mask layer to make itactive.

Open Linear Gradient tool (with black foreground/white background); click and dragline from foreground area to bottom of well-exposed sky to define gradient zone(adjust opacity slider if necessary to control intensity).

Click eye in Sky level to compare results; merge down layers (Layers>Merge Down). Retouch using history brush.


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Mouse grab the upper corner handle arrow and move inward to align crop edge withconverging verticals; use middle handle to move horizontally to check alignment;return crop to frame edge.

For symmetrical crop turn on rulers (View>Show Rulers or Ctrl + R); align right crop. Hit Enter.

RECOMPOSITION

28. Distracting Elements

Note: Examine the image for distracting elements, e.g. branches, hot spots, clutter, etc.

With PS7, click on Background Layer to make it active Use the patch tool (J) set to Source to remove a small element where blending is

desirable; circle the element (shift-drag to add to selection; alt-drag to subtract) (or usethe Magnetic Lasso, freeform Lasso, etc.) and drag selection to an area from whichyou want to sample.

Use healing brush to clean up. With PS6 or where blending is undesirable, click on Background Layer to make it

active Select the item to be removed using one of the tools above, e.g. Magnetic Lasso,

Lasso, etc. Press Q to create a Quick Mask; feather edges with gaussian blur

(Filter>Blur>Gaussian Blur) with radius 5-10 or higher depending on resolution; pressQ to activate selection.

Use the selection tool to move the selection to an area to be copied remembering thelocation.

Choose Layer>New>Layer via Copy (or Ctrl + J); move the selection back over thecluttered area; dress up edges with clone tool.


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Sometimes addin g elements works. By maskin g the eagle, a patr iotic background l ayer wascombin ed, set at Soft l ight with L umi nosity 15%.

CROP AND RESAMPLE

29. Final Crop

Set snap to (View>Snap checked)(View>Snap to>Document Bounds checked). Create duplicate layer (Layer>Duplicate Layer). Open crop tool (or press C), clock on Front Image. Adjust width and height to target dimensions; select Shield cropped area. Drag rectangular marquee to select image to retain; drag handles to adjust (hold down

CTRL to turn off snap). Place cursor just outside bounding box (and inside image) to rotate. If perspective has not been corrected above, check Perspective box on options bar;

move each corner of the cropping rectangle independently; hold down Space bar tomove image within outline.

Click Hide radio button (only revealed in layered file); click on check, double clickimage or press Enter to crop (Esc to cancel).

To view hidden pixels, Image>Reveal All. Save file in PFD format to preserve hidden pixels as Master or in new directory, Final

Images.

Note: When up-sampling substantially, increase image size in increments (stairinterpolation) for better results.

30. Resampling

Note: resampling effects both size and resolution as compared to resizing whichmaintains the same pixel dimensions.

Flatten Image (Layer>Flatten Image). Save file in Genuine Fractals (STN) if this is available ( some believe fractal

resampling is better than Adobe bicubic) and reopen using GF settings.

Otherwise, choose Image >Duplicate (Merged Layers Only). Open Image>Image Size; click on Width then Height arrows and choose inches; setsize and resolution. ( Note: for inkjet printers use 300ppi, for Lightjet, 304.8; otherwise the resolution of the printer); OK.


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SHARPENING AND CLEANUP

31. Final Sharpening / Examination

Note: Images acquired from a scanner or digital camera will almost always benefit from

judicious sharpening. Sharpening should be done after all retouching and resizing, and isthe last operation before Color Management takes over. Final sharpening should be donewith size, viewing and printing parameters in mind. If available, use nik Sharpener to sharpen to image size and resolution (set on Anna). Otherwise, for Lightjet 5000 (andcontinuous tone printers) sharpen so image looks well on screen, slightly over-sharpen for inkjets (dithered). Note: It is usually advantageous to mask out continuous tone areas to avoid sharpening grain, or to sharpen highlights and shadows separately through selections as above.

Open new view (View>New View); zoom in on critical area. Open unsharp filter (Filter>Sharpen>Unsharp Mask)(do not use Sharpen, Sharpen Edges,

or Sharpen More). Place preview box in critical area and set zoom (+/-) to monitor effects (you now have

three views). Set Amount (volume control; interacts with Radius to set degree of sharpening)

temporarily to 500%; set Radius (width of edges) to final resolution divided by 150(75ppi = 1.0; 300ppi = 2.0); fine detail needs less.

If using a 35mm scan, move sample box to smooth, continuous tone; if indicated, raiseThreshold (delta of tonal values) carefully to point where grain and noise are notsharpened; detailed landscapes 0 inanimate objects 0-1, average 2-3, faces may need upto 5 Threshold; to restart use Ctrl-Z.

Return to Radius and set at point where detail is emphasized. 31.7. Finally, decrease Amount to between 120-400 (faces 70-100, fine detail higher) and

monitor results.

Note: Lightjet sharpening for 16x20 print would be about amt. 300, radius 0.5, andthreshold 0-2. Web sharpening should be about 200%, .5, 0.

Now choose cancel and reopen Unsharp Mask, which will contain your same settings. Open color channels (Windows>Show Channels); click on Red and shift-click on Green

(Blue channel produces more noise) or choose lightest channel with least detail. . Divide the Amount determined above by four, and apply the filter four times monitoring

each step. Look for and repair any unwanted artifacts with clone tool. If the effect is too sharp, either backup one sharpening (Edit>Undo) or use Edit>Fade

Unsharp Mask set for Luminosity in drop-down menu at e.g., 50% (experiment withsetting).


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work flow of image processing

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