# Images

Exploring images in computers

TAGS: Computers, Design, Free Gratis, Free Libre, Images, Open Source, Software, Standards, TECH

## Intro

Images or graphics are represented in computers as dots (pixels) of colors. Raster graphics deal with images using pixels; Vector graphics deal with images using math equations. Animation are still images over time. Computer modeling in 2D and 3D are essentially more complex vector images (EG: Blender and SketchUp).

Most operating systems come with a simple image viewer, EG: Windows Explorer can view images. Some image viewers also manage pictures with tagging and such, EG: Picasa. Some image viewers also view animated files (GIF89) or even videos, EG: IrfanView.

Most operating systems come with a simple image editor, EG: Windows comes with Paint. The most famous powerful raster graphic editors are Photoshop (not free) and GIMP (free). The most famous powerful vector graphic editor are Illustrator (not free) and Inkscape (free). Some graphic editors (like ACD Canvas) do both raster and vector.

## Key Concepts

Some key concepts in images and image editing in computers.

Pixels. Aka px. A pixel refers to the smallest addressable element in an image, image output device (EG: Display), or image input device (EG: Camera or scanner). An image or display consists of a grid of pixels. EG: A 800 pixel wide by 600 pixel high image has an image resolution of 800x600.

Pixel Resolution. Pixel resolution refers to the pixel count of an image. Here are common representations of resolution:

• Height by Width. HxW is the most common representation of resolution. EG: A phone might be 320x240, a monitor 1024x768, a TV 1920x1080.
• Height. Common in recent TVs. EG: A phone might be 240, a monitor 768, a TV 1080.
• Display resolution name. Especially for computer monitors. EG: A phone might be QVGA, a monitor XGA, a TV HD 1080.
• Pixel count. Common for digital cameras. EG: A 3.1 Mpx camera may have a CCD or CMOS image sensor with 2048 * 1536 sensor elements.

Spatial Resolution. Aka optical resolution or visual resolution. This is a measure of the clarity or fuzziness of an image. EG: An image with high pixel resolution may have poor spatial resolution if the image is out of focus or appears pixelated/blocky because the viewer is too close. Other problems can arise when the viewer is too close (or the display is too large), including the following: The viewer has to turn their head too much, and the viewing surface goes too far from perpendicular to the viewer.

Pixel Density. Pixels per inch (ppi). An image of a specific pixel resolution will have a higher pixel density on a smaller display than a larger display. Assuming the image is in focus, the appropriate pixel density needed to have good spatial resolution will depend on the physical display size, the distance between the display and the viewer, and personal preference. EG: A 1080 workstation display viewed from an arms length should have be 72-96 ppi, i.e. say 18-26" diagonal, but a 1080 TV display viewed from 6' away should be say 50 ppi, i.e. roughly 36-46" diagonal. Note that some files (like GIF) are fixed at 72 ppi.

Print Quality. Dots per inch (dpi) or dots per cm (dpcm). Print quality is similar to pixel density, but frequently more than one dot of ink is required for each pixel in an image. EG: Dot matrix printers are 60-90 dpi, inkjets printers are 300-600 dpi, and laser printers are 600-1800 dpi. Typically a ppi of less than 100 should be reserved for large print that is always viewed from a greater distance. 200 ppi and above is usually good enough to avoid blockiness in most hand held printed material.

Points. A point is a unit of measurement common in printing and font sizes. 12 points = 1 pica. 72 points = 6 pica = 1 inch.

Color. In computers a color is mix of different amounts of three primary colors: red, green, and blue (RGB). Each primary color goes from no color (0) to full saturation (1, 255, xFF, or 100%). While computers use the RGB color model, print typically uses the CMYK color model, and there are other color models, EG: HSV, YUV, and YCbCr.

Foreground Color (aka FG). This is the color of the "pen", "brush", and outline of text.

Background Color (aka BG). This is the color of the "eraser" and shape fills.

Color Profile. A "color" on one device may differ on another device. Color profiles are created for specific devices (by make and model) so that they can sync with a device-independent color space defined by the International Color Consortium (ICC). If in doubt choose the sRGB color profile.

Compositing. Compositing are the various techniques of combining images. There are many older techinques, concepts, and words from painting, photography, and film that predate comptuers. EG: The painter's algorithm is to paint distant objects first.

Layers. Simple images have one layer. Composite images have multiple layers, each like a transparent sheet of paper. The order that the layers are stacked can be changed. A layer may be hidden or shown. Parts of a layer may have varying degrees of transparency via the alpha channel. New images usually start with one layer (the background layer) with no alpha channel. A layer type depends on its channels. The layer types include: RGB, RGBA, Gray, GrayA, Indexed, IndexedA.

Channels. A channel is a single component of a pixel. A channel typically has a value from none (0) to full (usually 8 bits, 255, xFF, 1, or 100%). A channel also refers to the grid of values for a channel of the image, EG: An 800x600 layer typically has 4 channels (RGBA), where each channel is 800x600 so that an RGBA tuple (R, G, B, A) can be assigned to each pixel. Here are the typical channels:

• Bilevel Channel. 1 bit per pixel. Most channels have 8 bits (0-255).
• Red Channel. No red to full red.
• Green Channel. No green to full green.
• Blue Channel. No blue to full blue.
• Gray Channel. No black to full black. For images in grayscale mode.
• Alpha Channel. No masking (transparent layer) to full masking (opaque layer). A checkered backdrop is often used to indicate degree of masking/transparency.

Bit Depth. Bit depth refers to the number of channels an image has. EG: An RGB image has 24 bit depth because its 3 channels each have 8 bits.

Modes. The mode of an image is related to its channels:

• RGB Mode. The typical default mode. RGB is "flat", i.e. without an alpha channel.
• Grascale Mode. For grayscale images.
• Indexed Mode. For images where each pixel has a color from a fixed palette or colormap of up to 256 colors. Used when aiming for a smaller file size. Generally speaking a palette is used to make an image, while a colormap is derived from the colors in an image.
• Bilevel Mode. Old school! Really small size.

Masks. Masking is a compositing technique that selects parts of layers to be combined by covering or revealing the parts.

• Binary masking is when only full or no transparency is used, EG: A physical mask with cutout eyeholes. EG: GIF supports only binary masking.
• Alpha compositing masking is when the transparency has a spectrum of values from full to no transparency, EG: A physical mask with gauze eyeholes.
• Layer Masking. An image or layer can have an Alpha channel for controlling the transparency of each pixel in the image or layer. Values range from no masking (0, transparent, black) to full masking (255, opaque, white). Note that a layer can have an alpha channel and a layer mask!
• Selection Masking. Selection Masking is like a channel for specifying the parts of an image or layer that you will work on. Values range from no selection (0, black) to full selection (255, white). An animated dotted line ("marching ants") indicates the borders of selection. In simple editors like paint, it is binary masking. In editors like GIMP and Photoshop, the border is at 50% selelction.

Metadata. Metadata is data about data. Image metadata includes things like caption, credits, creation date, and location. Some editors by default wipe out image data when saving. As of 2011, the most common image metadata formats include the following:

• Exchangeable image file format (Exif). Common in digital cameras.
• International Press Telecommunications Council (IPTC).

Crop. To crop an image or layer is to select the parts of an image to retain. Hard cropping discards data, while soft cropping hides the extra data.

Brush. A brush is a pixmap (image) or set of pixmaps used in painting. When a paint tool (EG: Pencil, paintbrush, eraser, airbrush) uses a brush, the pixmap is applied to the image.

Gradient. A gradient is a set of colors or opacities or both arranged in order. A gradient can be put in selections or used with a paint tool. Gradients are usually in linear order but may be conical, spiral, selection shaped, etc.

Pattern (aka texture). A pattern is a small image for filling regions by tiling. A pattern is tileable if the tiles are seamless. Patterns are typically used with tools like bucket, paint, or clone. Patterns may also be used when stroking paths.

Paths. In vector graphics paths (aka lines; curves) consist of one or more components, each of which may contain one or more segments. Components may be disconnected from each other. Segments are two connected end points (aka knots; anchors; outer control points) with no points in between. A segment is a Bézier curve. Bézier curves (aka splines; segments) are parametric curves. Each end point of a segment has a vector (aka handle; inner control point) with direction and magnitude describing the curve from the end point. If a segment is a straight line, the its handles have zero length. A component or path with all straight segments is polygonal. If a component connects is first and last points, then it is "closed", other wise it is an "open" component.

Stroke. Stroking a path applies styling to a path. EG: Thickness, cashes, and color.

## Image File Formats

Here are some of the major image file formats. There are, of course, many other image file formats. For the Web, the rule of thumb is JPEG for photos and PNG for files with fewer colors.

### GIF

Graphics Interchange Format (GIF).

• Primary use: Best format for short animations with fewer colors. Good for small images with few color, although PNG does that too but with better compression, true color, and alpha transparency.
• Filename extensions: .gif.
• Format: Raster image.
• Internet media type: image/gif.
• Modes: Indexed mode for palette/colormap of up to 256 colors.
• Compression: LZW lossless data compression.
• Animation: Yes. Aka gif89a. Each frame can have its own palette.
• Progressive display: Yes. Can be interlaced for progressive image display while loading, but the GIF files are usually so small and modern speeds are so fast that interlacing is moot.
• Transparency: Supports binary masking by allowing 1 color to be designated as transparent.
• Magic number: GIF87a or GIF89a. In the first 6 bytes.
• Max size: Not sure. Roughly 500x500 = 250 Kpixels.
• Miscellany: GIF files can internally store a comment composed of 7-bit ASCII characters. Output is fixed at 72 ppi.

### JPEG

Joint Photographic Experts Group (JPEG).

• Primary use: General still images, photos. JPEG/Exif is probably the most prevalent raster image format. For exact data reproduction, use a lossless format instead.
• Filename extensions: .jpg, .jpeg, .jpe, .jif, .jfif, .jfi.
• Format: Raster image.
• Internet media type: image/jpeg.
• Modes: RGB.
• Compression: Lossy compression. Very good, sometimes 10:1 compression without much loss in spatial resolution. JPEG actually refers to the JPEG compression standard. The JPEG standard has a lossless mode that practically no one uses. Beware of generational loss.
• Animation: No.
• Progressive display: Yes. Uses Adam7. Can be interlaced for progressive image display while loading, but many programs don't support it.
• Transparency: N/A.
• Magic number: ff d8 in the first 2 bytes.
• Maximum image size: 65,535 x 65,535 ~ 4.29 Gpx.
• Miscellany: May have Exif metadata. Smoothing may get rid of some lossy artifacts but it generally also blurs the image.

### ORA

OpenRaster (ORA).

• Primary use: For exchanging layered images between raster image editors
• Filename extensions: .ora.
• Format: Raster image, but can also store paths, fonts, multiple pages, undo history, Exif metadata. An .ora file is basically a zip folder with 4-5 sections: mimetype, stack.xml (with layers metadata), data (typically .png referenced by stack.xml), thumbnails (as .png), and an optional mergedimage.png.
• Internet media type: image/openraster.
• Modes: bilevel, RGB, grayscale, indexed.
• Compression: Zip.
• Animation: Yes.
• Progressive display: Sort of as .png.
• Transparency: Supports alpha channel.
• Magic number: ?
• Maximum image size: ?
• Miscellany: Meant to replace the Adobe Photoshop .psd file format since Adobe restricted the .psd license in 2006. As of 2013-02-03 these apps support .ora: MyPaint, GIMP, Kirta, Pinta, XnView.

### PNG

Portable Network Graphics (PNG).

• Primary use: For small images with few colors (like buttons and icons). Use for general still images, photos, especially when size is not as important as good data quality and no artifacts.
• Filename extensions: .png.
• Format: Raster image.
• Internet media type: image/png.
• Modes: RGB, RGBA, grayscale, grayscale + Alpha, indexed.
• Compression: Lossless compression.
• Animation: Sort of. MNG and APNG should do animation but are not well supported. Internet Explorer supports MNG.
• Progressive display: Yes. Can be interlaced for progressive image display while loading. Uses Adam7 interlacing algorithm.
• Transparency: Supports alpha channel.
• Magic number: 89 50 4e 47 0d 0a 1a 0a in the first 8 bytes.
• Maximum image size: The IHDR chunk uses 4 bytes to store image width, height, and bit depth.
• Miscellany: Developed as a reaction the 1995 patent problems by Unisys for GIF that eventually blew over.

### SVG

Scalable Vector Graphics (SVG).

• Primary use: 2D vector images with some raster images and text. Since it's an XML file, it can be scripted for things like animation.
• Filename extensions: .svg, .svgz.
• Format: Vector image. Can contain raster images and text too.
• Internet media type: image/svg+xml.
• Modes: N/A.
• Compression: As much as you can compress an XML file.
• Animation: Not directly. Sequences of SVG images can be made animated. HTML5!
• Progressive display: No.
• Transparency: No
• Magic number: N/A
• Maximum image size: None in theory.
• Miscellany: SVG is an XML file so it can be scripted, searched, indexed, and compressed.

### TIFF

Tagged Image File Format (TIFF).

• Primary use: General still images, photos, especially when size is not as important as good data quality and no artifacts. Not recommended for web use.
• Filename extensions: .tiff, .tif.
• Format: Raster and vector image.
• Internet media type: image/tiff. image/tiff-fx.
• Modes: bilevel, RGB, grayscale, indexed.
• Compression: Lossless LZW compression, but various compression schemes can be used.
• Animation: No.
• Progressive display: No.
• Transparency: Supports alpha channel.
• Magic number: 1 byte for byte order (either "II" for little-endian or "MM" for big endian), followed by 2 bytes for "42". Yes, it's a Hitchhikers Guide to the Galaxy reference.
• Maximum image size: 4 Gbytes.
• Miscellany: Can store multiple/multi-page images or subfiles. May have Exif metadata. TIFFs can do other funky stuff but then that goes beyond the scope of just an image.

### WEBP

WebP (pronounced "weppy").

• Primary use: Created by Google in 2010 as an open standard for images with lossy and lossless compression. A sister project to WebM, both derived from VP8.
• Filename extensions: .webp.
• Format: Raster image.
• Internet media type: image/webp.
• Modes: 8 bit color, color profiles.
• Compression: Lossy or Lossless. Supposedly better than JPG (26%), PNG (30%), or GIF.
• Animation: Yes.
• Progressive display: ?
• Transparency: Supports alpha channel.
• Magic number: WEBP
• Maximum image size: 14 x 14 bits = 16384 x 16384 pixels = 268,435,456 pixels ~ 2.6 Mpixels.
• Miscellany: With the above plus EXIF metadata and backing by Google and most browsers, WEBP is positioned to beat out JPG, PNG, and GIF! Google has all sorts of converters available [https://developers.google.com/speed/webp/].

### Other Image File Format

Bitmap (BMP). Aka Device Independent Bitmap (DIB). BMP is an older and now minor image file format common in Windows and OS/2, that tends to have large file sizes for a given pixel resolution.

PICT is an older and now minor image file format common in older Apple Macintosh computers.

Photoshop Document (PSD). Aka PhotoDeluxe (PDD). The native file format for the Photoshop app.

eXperimental Computing Facility (XCF). The native file format for the GIMP app. Save all the info (layers, transparence, etc. but not undo history). Edit in xcf as needed, then export to a format like JPEG, PNG, GIF, TIFF, etc.

RAW. An image file from a digital camera that has been minimally processed. RAW files tend to be very large. There are many filename extensions including: .3fr, .ari, arw, .srf, .sr2, .bay, .crw, .cr2, .cap, i.iiq, .eip, .dcs, .dcr, .drf, .k25, .kdc, .dng, .erf, .fff, .iiq, .mef, .mos, .mrw, .nef, .nrw, .orf, .pef, .ptx .pxn, .R3D, .raf, .raw, .rw2 .raw, .rwl, .dng .rwz, .srw, .x3f

## Image Viewers and Organizers

All image organizers are also image viewers, but not all image viewers are image organizers. Most image viewers and organizers usually do at least minor raster image editing.

To look at images in a computer, people probably use an image viewer/organizer that comes with their computer, and then further organize/manage their image files with the file manager that comes with their operating system.

For example: As of 2014-04, I use the following:

• Image Viewer: IrfanView [irfanview.com]. This image viewer is free (gratis) and very fast. Views most images as well as animated GIFs, Flash files (.swf), PDFs, video, and audio. It also comes with IrfanView Thumbnails which gives the suite some image organizer capabilitie like view files in directories, make contact sheets, and combine images into panoramas.
• Image Viewer: FastStone Image Viewer [http://faststone.org/FSViewerDetail.htm]. Mainly because you can click on thumbnails and it animates GIFs without opening up a separate window.
• Image Organizer: Windows Live Photo Gallery (WLPG). This image organizer cam with Windows 8 so it effectively free (gratis) for me. I had also considered using Goolge Picasa. Both do Captions, Ratings, Flags, Geo Tagging, People Tagging, and Tag Hierarchies, but neither plays animated GIFs. Picasa has some nice other features (like tie-ins to online stuff) but it's a perpetual resource hog, while WLPG is fast and efficient. WLPG doesn't view or tag GIFs but I can live with that.
• File Manager: Since I have Windows 8, I also do image organizing with Windows Explorer. There are so many different ways to organize images: By time, by media type, by projects, by originals v derivations, by categories. However lately I organize by time (year, month).
• Utility for finding duplicate files: Awesome Duplicate Photo Finder [http://www.duplicate-finder.com/photo.html]. It's free (gratis). Works with .bmp, .jpg, .gif, .png, tif. Can search subdirectories. Get's approximate matches too.
• Utility for renaming lots of files: Bulk Rename Utility [http://www.bulkrenameutility.co.uk/]. Can be used for any kind of file, not just image files. Free (gratis) and proprietary.

As far as image organizers, here are some (roughly ordered by price):

• Photoshop Lightroom by Adobe. Cross platform, commercial and proprietary.
• Aperture by Apple. For Mac OS X, commercial and proprietary.
• Windows Live Photo Gallery (WLPG) by Microsoft. Comes with Windows.
• iPhoto by Apple. Simple image organizing. Comes with the MacOS X.
• Picasa by Google. Cross platform, free (gratis) and proprietary.
• digiKam. Cross platform, free (gratis) and open source (free libre).

See these related links at Wikipedia:

## Image Editors

Image editors come in two major flavors:

• Raster. For editing images by manipulating representations of pixels. EG: Photoshop (proprietary) and GIMP (free). Rasters are 2D, but 2D images can be laid on 3D models.
• Vector. For editing images by manipulating representations of geometric shapes. EG: Illustrator (proprietary) and Inkscape (free).
• 3D computer graphics software are speciallized vector image editors for 3D computer generated imagery (CGI).
• Computer aided design (CAD) editors are speciallized vector image editors for architecture, engineering, construction, and engineering. CAD can be 2D or 3D. Software for 3D printing and rapid prototyping fall in this category.
• Both. There are some image editors that try to cover both raster and vector images. EG: Adobe Fireworks, Adobe Photoshop CS6 Extended, and ACD Canvas.

The list above can be converted to a flat list of five kinds of image editors:

• Raster
• Vector
• Raster/Vector
• CGI

Editors that deal with sequential still images over time are not really image editors any more but editors for video and animation.

I have only used a few image editors, but I want to review some of the major ones to have perspective. I am ordering them roughlyl by price. My personal favorites as of 2013-01-20 are in bold.

• Raster
• Photoshop by Adobe. The nearly undisputed king of raster image editing. Since 1989. Photoshop Elements is the hobbyist version. There are other versions and ways to buy it (like subscription or as part of a suite). As of 2013-01-20: Photoshop CS6 is $699, and Photoshop Elements is$99. Since 1989. Cross platform, commercial and proprietary.
• Painter by Corel. Emulates traditional media technques and free hand drawing. Lighter version exist. As of 2013-01-20: Painter 12 is $249, Painter Lite is$69, Painter Essentials 4 is $60, and Paint It! is$40. Cross platform, commercial, proprietary.
• PaintShop Pro by Corel. Formerly Paint Shop Jasc Software. Since 1990. As of 2013-01-20 PaintShop Pro X5 Ultimate is $80. For Windows, commercial and proprietary. • SmoothDraw [smoothdraw.com]. For easy and natural free hand drawing. Used in the beloved videos by Khan Academy. For Windows, free (gratis) and proprietary. • Paint.NET [getpaint.net]. Intuitive. Does layers. Windows, free (gratis) and proprietary. • Pixelmator [pixelmator.com]. Intuitive. As of 2013-01-21$15. Lots of features. Mac OS X, commercial, proprietary.
• PaintTool SAI [systemax.jp/en/sai/] by Systemax. Like Corel Painter, PaintTool SAI emulates traditional media techniques. Because this software is Japanese, it is popular in the manga/anime community. As of 2013-01-22 PaintTool SAI is 5250 JPY or $59. Windows, commercial, proprietary. • pixlr [pixlr.com]. An online or mobile raster editor. Cross platform, free (gratis) and proprietary. • Paint. Paint or whatever simple raster editor comes with your system. Not a gazillion features but fast and easy. • MyPaint [mypaint.intilinux.com]. Like Corel Painter, MyPaint emulates traditional media techniques. Cross platform, free (gratis), open source (free libre). • GIMP. Very powerful. Cross platform, free (gratis) and open source (free libre). • Vector • Visio by Microsoft. 2D vector specialized for charts, network diagrams and the like. Variations include Standard, Pro, and Premium. As of 2013-01-20: Visio Professional 2010 is$560, Visio Premium 2010 is $999. • Illustrator by Adobe. Powerful. Adobe absorbed Macromedia Freehand. As of 2013-01-20: Illustrator CS6 is$599. Cross platform, commercial and proprietary.
• CorelDRAW by Corel. As of 2013-01-20 only available as part of the the CorelDRAW Graphics Suite X6 which includes other products (see below). Windows, commercial, proprietary.
• Dia. Comparable to Visio. Cross platform, free (gratis) and open source (free libre).
• DrawPlus [serif.com/drawplus] by Serif. Intuitive. Can also make Flash animations. As of 2013-01-21 DrawPlus X5 is $100, DrawPlus Starter Edition is$0. Windows, commercial, proprietary.
• Google Drive by Google. Web based Google Drive can make simple 2D vector drawings. Cross platform, free (gratis), and proprietary.
• Inkscape. Comparable to Illustrator. Cross platform, free (gratis) and open source (free libre).
• Draw in OpenOffice and Libre Office. Basic 2D vector drawings. Cross platform, free (gratis) and open source (free libre).
• Raster/Vector
• Photoshop C6 Extended by Adobe. 2D and 3D. As of 2013-01-20: Photoshop CS6 Extended is $999. Cross platform, commercial and proprietary. • CorelDRAW Graphics Suite X6 includes CorelDRAW (vector), Photo-Paint (raster), and more. 2D. As of 2013-01-20: CorelDRAW Graphics Suite X6 is$499. Windows, commercial, proprietary.
• Fireworks by Adobe. For fast prototyping for 2D mobile, web, and apps. Cross platform, commercial and proprietary.
• Krita [krita.org]. Like Corel Painter, Krita emulates traditional media techniques. Linux (but trying to port to Windows), free (gratis), open source (free libre).
• Fatpaint. A web based app but it has tons of ads and may be a source of malware.
• CGI. There are so many here and it's not my specialty so I'll only mention what pops up.
• Blender [blender.org]. 3D CGI animation and effects. Cross platform, free (gratis) and open source (free libre).
• ZBrush [pixologic.com/zbrush/] by Pixologic. Digitl sculpting, 3D/2.5D modeling, texturing and painting. Pixologic ZBrush has an emphasis on sculpting like Corel Painter has an emphasis on traditional media techniques. Pixologic bought Sculptris which is similar but is like clay modeling. ZBrush is a level above Sculptris in detail and such. As of 2013-01-28: Sculptris is $0, ZBrush 4R5 is$699. Cross platform, commercial (although Sculptris is free), and proprietary.
• KeyShot [keyshot.com]. Software renderer (instead of hardware rendering).
• CAD. There are so many here and it's not my specialty so I'll only mention what pops up.
• AutoCAD by Autodesk. 2D and 3D CAD and drafting. It's the CAD that I've heard of the most. As of 2013-01-20 AutoCAD 2013 is $4195. Cross platform, commercial, proprietary. • Designer by Corel. 2D and 3D technical illustrations. As of 2013-01-20: DESIGNER Technical Suite X5 is$999. Windows, commmercial, proprietary.
• Canvas by ACD. 2D. Does raster too. Formerly owned by Deneba. The emphasis has shifted form general illustrations to technical illustrations. I used this for a long while but haven't used it in ages. As of 2013-01-20 Canvas 14 Standard is $600, Canvas 14 with GIS is$800. Windows, commercial, proprietary.
• CorelCAD by Corel. 2D and 3D. As of 2013-01-20: CorelCAD 2013 is $699. Cross platform, commercial, proprietary. • SketchUp [sketchup.com] by Trimble Navigation. 3D architectural. Google sold this to Trimble in 2012-04. As of 2013-01-20: SketchUp is$0, SketchUp Pro is \$495. Cross platform, commercial and proprietary.

See these related links at Wikipedia:

## GIMP

GNU Image Manipulation Program (GIMP) is a free (gratis and libre) and cross-platform raster graphics editor.

### Selections

To cut and move a selection: CTRL+ALT.

To copy and move a selection: SHIFT+ALT.

To add to a previous selection: Hold SHIFT while making a selection.

To subtract from a previous selection: Hold CTRL while making a selection.

To get the intersection of selections: Hold SHIFT+CTRL while making a selection.

In QuickMask, red indicates not selected. Degree of selection is done by painting from no selection (0, black) to full selecton (255, white). Selections can be saved to one or more selection channels. Selections can be copied and pasted.

When a selection is copied or cut, it is automatically made avialable as a brush.

### GIMP Extensions

.xcf is a native GIMP file. Use it to save all the info (layers, transparence, etc. but not undo history). Edit in .xcf as needed, then export to a format like JPEG, PNG, GIF, TIFF, etc.

The extension of GIMP brushes include .gbr (regular and color/image brushes), .gih (image hose, i.e. animated), and .vbr (parametric brushes). Google "GIMP brushes".

.pat is for GIMP patterns. GIMP can also use PNG, JPEG, BMP, or TIFF files as patterns.

### Miscellany

GIMP can import SVG paths and open SVG files as GIMP images.

If your copy and paste creates a floating selection, i.e. a temporary layer, then it must be anchored to an existing layer or converted to a new layer.

GIMP can be scripted with Script-Fu (a dialect of Scheme/Lisp). Every statement is surrounded by parentheses. The function/method/operator is the first item in the parentheses, and any other items are parameters. Place your scripts in the scripts directory of gimp user install.

; comment
(+ 3 4 5) ; prefix notation
(let* ( (a 1) (b 2) ) (+ a b)) ; local variables
(let* ( (a 3) ) (set! a (+ a a))) ; change value
(define (myFun a b) (+ a b)) ; define functions
(myFun (myFun 3 4) 5) ; call functions
(let* (a '(1 2 3)) a) ; list
(let* (x '("foo" (1 2 3))) x) ; lists can contain lists
(cons 1 '(2 3)) ; concatenate
(let* ((a 1) (b 2)) (list a b 3 4)) ; define list
(car '(1 2 3)) ; returns 1
(cdr '(1 2 3)) ; returns (2 3)


### Inkscape

Inkscape is a free (gratis and libre) and cross-platform vector graphics editor.

### Miscellany

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