how to reduce size of multiple images in photoshop

Image Optimization Techniques for Batch Processing

Image Resolution Adjustment

A core method for altering file dimensions. Resolution is typically expressed in pixels per inch (PPI). Decreasing PPI proportionally decreases file size.

Considerations

  • Intended Use: Web display requires lower resolution than print.
  • Image Quality: Lowering resolution excessively can introduce pixelation and loss of detail.

File Format Selection and Compression

Different formats offer varying levels of compression. Common formats include:

  • JPEG: Lossy compression suitable for photographs. Offers adjustable quality settings; lower quality results in smaller files.
  • PNG: Lossless compression, best for graphics, logos, and images with sharp lines or text. Typically larger than JPEGs for photographs.
  • GIF: Lossless compression limited to 256 colors, suitable for simple animations or graphics.
  • WebP: Modern image format offering superior lossless and lossy compression for images on the web.

Utilizing appropriate compression algorithms within each format is critical.

Color Depth Reduction

Decreasing the number of colors in an image can significantly reduce file size, especially for images with limited color palettes.

Indexed Color

Reduces colors to a specified number. Suitable for graphics and illustrations.

Image Scaling (Resizing)

Reducing the physical dimensions (width and height) of an image directly affects its file size. Scaling down is often necessary for web use.

Resampling Methods

Algorithms used to calculate pixel values during resizing. Common methods include:

  • Bilinear: Provides a balance between speed and quality.
  • Bicubic: Generally produces sharper results but is slower.
  • Nearest Neighbor: Fastest method, but can result in a jagged appearance. Best for pixel art or preserving hard edges.

Metadata Stripping

Images often contain embedded metadata (e.g., camera settings, location data, copyright information). Removing unnecessary metadata reduces file size without affecting visual quality.

Automated Batch Processing

Leveraging automation features significantly enhances efficiency when handling numerous images. This involves creating and applying repeatable actions.

Action Creation

Recording a series of steps (e.g., resizing, format conversion, quality adjustment) into a reusable action.

Batch Application

Applying the created action to a folder of images, automating the optimization process.