There are several ways to compress an image in Photoshop, depending on your desired outcome (file size vs. image quality) and the intended use of the image. Here are the most common methods:
1. Adjusting Image Size (Dimensions)
This method reduces the overall dimensions of the image, leading to a smaller file size.
- Open Your Image: Go to
File > Openand select the image you want to compress. - Access Image Size: Navigate to
Image > Image Size(or use the shortcutCtrl+Alt+Ion Windows orCommand+Option+Ion Mac). - Adjust Dimensions:
- Pixel Dimensions: Change the width and height. Make sure the "Resample" box is checked. Using "Automatic" for resampling usually works well. Experiment with other resampling methods (like "Bicubic Sharper" for reductions) to see what gives the best result for your particular image.
- Constrain Proportions: Ensure the "Constrain Proportions" icon (a link icon) is activated to maintain the aspect ratio of your image. This prevents distortion.
- Click OK: The image will be resized, and the file size will be reduced.
Example: Reducing a 3000x2000 pixel image to 1500x1000 pixels will significantly reduce its file size.
2. Saving for Web (JPEG, PNG, GIF)
This is the most common method for compressing images for online use, offering various optimization options.
- Open Your Image: Go to
File > Openand select the image you want to compress. - Save for Web (Legacy): Go to
File > Export > Save for Web (Legacy). - Choose File Format: Select the appropriate file format:
- JPEG: Best for photographs and images with many colors. Adjust the "Quality" setting to balance file size and image quality. Lower quality means smaller file size but more compression artifacts.
- PNG: Best for images with sharp lines, text, and transparency. PNG-24 supports more colors than PNG-8, but generally has a larger file size. PNG-8 is a good option for graphics with limited colors.
- GIF: Best for simple animations and images with limited colors (up to 256).
- Adjust Settings: Experiment with the quality settings, color reduction (for GIF and PNG-8), and other options to find the optimal balance between file size and image quality. Use the preview window to compare different settings.
- Click Save: Choose a location to save your compressed image.
Key Considerations for Save for Web:
- JPEG Quality: A quality setting of 60-80 often provides a good balance.
- PNG-8 Color Reduction: Reduce the number of colors if appropriate.
- Progressive JPEG: Enable "Progressive" for JPEGs to display a low-resolution version of the image while it's loading.
3. Save As (JPEG Options)
When saving as a JPEG directly, you have limited compression control compared to "Save for Web (Legacy)".
- Open Your Image: Go to
File > Openand select the image you want to compress. - Save As: Go to
File > Save As. - Choose JPEG: Select "JPEG" from the format dropdown menu.
- Adjust Quality Slider: A quality slider will appear. Drag it to the left to reduce the file size (and image quality) or to the right to increase the file size (and image quality).
- Click Save: Choose a location to save your compressed image.
4. Reducing Color Depth
For images with many colors, reducing the number of colors can significantly decrease file size. This is mostly relevant for formats like GIF or PNG-8.
- Convert to Indexed Color:
Image > Mode > Indexed Color. - Specify Number of Colors: In the Indexed Color dialog box, choose the number of colors you want to use. Fewer colors result in a smaller file size. Experiment with the Palette and Dither options to achieve the best visual result.
Choosing the Right Method
- For web use (photos): "Save for Web (Legacy)" with JPEG format is generally the best option.
- For web use (graphics with transparency or text): "Save for Web (Legacy)" with PNG format (PNG-8 or PNG-24) is typically the best choice.
- For general compression (with some quality loss): Adjusting Image Size or using "Save As" with the JPEG format.
- For reducing colors in graphics: Converting to Indexed Color
