Learn about the default image filters provided by Core Graphics for quick special effects and how to save image files in Preview for macOS with effects.
Apple’s Core Graphics (Quartz) 2D imaging subsystem offers a powerful API for creating, saving, and manipulating graphics, as well as handling text rendering through Core Text.
Quartz enables precise text rendering with subpixel precision and anti-aliasing, even on displays with limited resolution capabilities.
Quartz plays a crucial role in 2D imaging on Apple platforms like iOS and macOS, covering various aspects of graphics manipulation. Initially introduced with Mac OS X, Quartz remains one of Apple’s oldest frameworks.
The imaging model in Quartz revolves around compositing, allowing multiple graphics layers to be combined using transparency (alpha), manipulated, transformed, saved, printed, or displayed.
The Quartz Compositor manages image assembly and manipulation, including combining, rotating, transforming, and shaping images. The final assembled image is then rendered by the display engine onto a display or printer.
On macOS, the Window Server oversees image culling and obscuring to ensure that display images are confined to their respective windows.
The Window Server, in conjunction with the Quartz Compositor, handles the content assembly of windows on macOS.
By clipping images based on window boundaries, the Window Server optimizes rendering performance by only rendering visible portions of a window. This improves efficiency, especially when switching between windows on macOS.
Upon its release in 2000, Mac OS X boasted cutting-edge graphics technology and frameworks in the computer industry.
iOS devices leverage Quartz similarly to Macs, utilizing the same Quartz framework and APIs, although they lack a dedicated window server. Quartz powers most visual elements on both Mac and iOS platforms, including images, text, and interface components.
Apple introduced Quartz 2D Extreme in Mac OS X Tiger 10.4, allowing Quartz graphics processing to leverage a dedicated GPU. Subsequently, in 10.5, Quartz Extreme was rebranded as QuartzGL.
The Quartz Compositor utilizes QuartzGL to accelerate rendering if a dedicated GPU is available.
Apple previously offered the Quartz Composer app, which has been discontinued in recent times.
Based on geometry
Quartz calculates graphics based on mathematical models, offering close approximations of the visual output. Whether rendering bitmaps or vector graphics, Quartz leverages geometry for precise representation, enabling scalable design elements.
Vector graphics, characterized by geometry-driven calculations, ensure scalability to any size. Transformations such as rotations, warping, and scaling modify images or objects based on geometric properties.
Bezier curves define intricate shapes in vector graphics, facilitating precise control over curves and shapes. Fonts, using Bezier curve geometry, outline characters to enable size adjustments and maintain visual consistency.
Fonts are based on Bezier curve outlines, allowing individual character customization. Each font file contains instructions on rendering character outlines for a specific typeface.
Quartz Display Services
Quartz Display Services (QDS), a Quartz subsystem, primarily focuses on hardware display management. Initially a minimal API, QDS now encompasses various APIs for tasks like display identification, property configuration, and content streaming.
- Locating and identifying displays
- Adjusting display properties
- Configuring all displays collectively
- Screen capture
- Display content streaming
- Implementing fade effects
- Enabling display mirroring
- Applying gamma correction for color calibration
- Receiving display change notifications
Applications on macOS should incorporate mechanisms to respond to display changes and adjust window configurations accordingly. Each display in macOS is assigned a DisplayID (CGDirectDisplayID) for identification.
Data types
Quartz defines a range of primitive types for graphic calculations, including integers, floats, geometric entities (points, sizes, rectangles), paths, vectors, and transforms. These data types serve as fundamental building blocks for graphics manipulation in Quartz.
Display contexts, images, layers, colors, and fonts form essential data types within Quartz. A display context represents a graphics environment for rendering content, with each display usually associated with a unique context. Additional offscreen and composite contexts may also be created as needed.
Simple individual types compose most Quartz data types, like CGPoint representing coordinates with precision, and CGRect defining a starting point and dimensions. Originating from the two-point model, CGRect determines the fundamental geometry in 2D graphics systems.
Layers play a crucial role in Quartz, allowing independent graphical entities to be combined, manipulated, and animated. Core Animation, another Apple framework, utilizes layers (CALayer) for simultaneous graphics animation.
Adobe PDF portable document file.
PDFs
Although separate from Quartz in Apple platforms, PDF handling is integral for rendering and printing purposes. PDFs, initially an Adobe standard leveraging PostScript, align with Quartz for visualization and printing.
Quartz introduces the CGPDFDocument data type for managing PDF documents, sourced through the CGDataProvider type. These data types facilitate creating visual representations of PDFs for display and print operations.
CGPSConverter, a Quartz type, enables direct conversion between PDFs and legacy PostScript content. Legacy printers with embedded PostScript can process and print documents in both PostScript and PDF formats.
Apple offers additional frameworks like ImageKit, PDFKit, Quartz Composer (now deprecated), and Quick Look for image and file processing tasks.
Quartz and Preview
Preview, macOS’s default image and PDF viewer, extensively relies on Quartz for rendering and displaying content. Preview leverages Quartz’s capabilities for file compositing, transformation, and rendering on par with other Quartz-powered applications.
Quartz Filters (CIFilter) in Quartz facilitate the application of special effects during the display, save, or print operations of graphics and image files. PDFs can also benefit from image filters through Apple’s ColorSync technology integration.
Quartz offers a set of standard filters for applying photographic effects to images, with provisions for defining and utilizing custom filters. macOS includes a Filter Manager to manage image filters effectively.
CIFilters rely on the CIImage and CIContext data types in Quartz. CIImage serves as an image generator, accepting input images and producing new ones, while CIContext handles image manipulation for filter effects.
Apple’s standardized approach to filter effects through CIFilters ensures consistent application and performance across Mac platforms leveraging Quartz APIs.
After filter application, a modified CIImage is output for further processing. Additionally, CIColor can be applied to adjust the overall color tone of an image.
Apple’s built-in filters cover a range of effects, including geometric alterations, compositing, gradients, and lens effects. These filters are categorized and accessible through constants prefixed with “CI”.
Further details on Apple-defined Quartz filters can be explored in the CIFilterBuiltins.h SDK header file and external resources like the Core Image Filter Reference documentation project by Noah Gilmore.
Apple’s CIThermal filter in the CIFilter.io app by Noah Gilmore.
Applying Filters in Preview
Although Preview lacks advanced image editing features, it supports basic manipulations like scaling, rotating, and applying color adjustments. Filter effects, however, are limited in Preview’s current functionality scope.
Nevertheless, you can apply filters during file save operations in Preview using a predefined set of ColorSync Core Image filters provided by macOS. These filters are accessible through the Quartz Filter menu when saving files.
Select a file name, location, Format, and Quartz Filter, if the format supports it.
Preview’s filter options emphasize grayscale conversion, sepia tones, lightness adjustments, and file optimization, catering to limited but efficient image editing needs. PDFs, on the other hand, can be saved in a PDFX-3 format suitable for professional print requirements.
While Preview’s filter set is modest, it offers a quick and straightforward way to enhance image files during save operations. Expansion of filter options in Preview would further augment its utility for image editing tasks.
Core Image and Quartz capabilities present intriguing opportunities for seamless image processing with future potential for broader support across macOS and iOS platforms. For Quartz programming enthusiasts, exploring resources like the legacy Quartz 2D Programming Guide and external references like Programming with Quartz: 2D and PDF Graphics in Mac OS X can provide valuable insights and expertise.