How to Convert Images Between Formats with Mac Preview

Images arrive in formats that do not always fit the job: a website demands JPG but your screenshot is a PNG, a form accepts only PDF, or a photo is in Apple’s HEIC format that a Windows PC cannot open. On a Mac you do not need converter websites or extra software — the free Preview app converts images between all the common formats in a few clicks, and it can resize and compress them at the same time. This guide shows the single-file method, the batch method for converting many images at once, and how to choose the right format every time.

Quick Answer

Open the image in Preview, choose File, then Export. In the Export dialog pick a format — JPEG, PNG, PDF, TIFF, or HEIC — adjust the quality slider if one appears, and click Save. To convert many images together, select them all in Finder, open them in one Preview window, select every thumbnail in the sidebar, then use File, then Export Selected Images.

Which Format Should You Choose?

Picking the format first makes the rest of the steps obvious:

• JPEG (JPG) — the universal choice for photos. Small files, works everywhere, but loses a little quality each time you save. No transparency.
• PNG — best for screenshots, logos, and graphics with text. Perfectly sharp and supports transparency, but photo files are large.
• HEIC — Apple’s modern photo format from iPhones. Very small files, but older Windows PCs and some websites cannot open it. Convert to JPEG for sharing.
• PDF — turns the image into a document page. Ideal for forms, ID scans, and anything you will print or sign.
• TIFF — a large, lossless format used in printing and archiving. Rarely needed for everyday sharing.
• GIF — only for simple animations or very basic graphics; a poor choice for photos.

Convert One Image, Step by Step

1. Double-click the image to open it in Preview. If another app opens it, right-click the file, choose Open With, then Preview.
2. Choose File, then Export. (On some versions it is Export As.)
3. In the dialog, set the file name and location at the top.
4. Click the Format dropdown and choose your target format. If you do not see the format you want, hold the Option key while clicking the dropdown — Preview reveals extra formats such as GIF, TIFF variants, and Microsoft BMP.
5. For JPEG, drag the Quality slider: towards Least for small email-sized files, towards Best for printing. The dialog shows the estimated file size as you drag — aim for under 1–2 MB for web uploads.
6. Click Save. A converted copy is created; your original stays untouched.

Apple’s Preview image conversion guide on Apple Support lists the formats each macOS version supports.

Resize an Image While You Convert

Oversized dimensions are the other reason uploads get rejected. Shrink the image before or during export:

1. With the image open in Preview, choose Tools, then Adjust Size.
2. Enter a new width — 1600 pixels is plenty for most websites and documents — and keep the “Scale proportionally” box ticked so the height follows automatically.
3. Click OK, then Export in your chosen format as described above.

Reducing a 6000-pixel camera photo to 1600 pixels wide, saved as a mid-quality JPEG, commonly cuts the file from 8 MB to under 500 KB with no visible difference on screen.

Convert Many Images at Once (Batch Method)

Converting a whole folder one file at a time is nobody’s idea of fun. Preview can do the lot together:

1. In Finder, select all the images (Command + A for a whole folder, or Command-click for a chosen set).
2. Right-click and choose Open With, then Preview. All images open in a single window, listed as thumbnails in the sidebar. If the sidebar is hidden, choose View, then Thumbnails.
3. Click the first thumbnail, then press Command + A to select every thumbnail in the sidebar. This step is the one everyone forgets — without it, Export converts only one image.
4. Choose File, then Export Selected Images.
5. Choose a destination folder (a new empty folder keeps things tidy), click Options if shown to set the format and quality, then click Choose.
6. Preview writes a converted copy of every image into that folder.

Fifty iPhone HEIC photos become fifty shareable JPEGs in under a minute with this method. If those photos later need renaming into a clean sequence, our guide on renaming many files at once on Mac finishes the job in seconds.

Convert an Image to PDF — and Back

To turn an image into a PDF, open it in Preview and choose File, then Export, and select PDF as the format. To combine several images into one multi-page PDF, open them together in one Preview window, select all thumbnails, then choose File, then Print, and use the PDF button at the bottom of the print dialog to Save as PDF — each image becomes a page in order.

Going the other direction — PDF page to image — open the PDF in Preview, drag the page’s thumbnail to the desktop, or Export with JPEG/PNG selected to render that page as a picture at screen quality.

Common Mistakes and Helpful Tips

• Converting a JPEG to PNG expecting better quality. Conversion cannot restore detail the JPEG already threw away; the PNG will just be a bigger file with the same quality.
• Forgetting to select all thumbnails in batch export. If only one file comes out, this is why — select the thumbnails, not just the images in Finder.
• Saving over the original. Export always creates a new file, but choosing the same name and folder will replace the original. Convert into a separate folder when the original matters.
• Uploading HEIC to older websites. If a site rejects your iPhone photo, convert it to JPEG first — HEIC support outside Apple devices is still patchy.
• Quality slider at maximum for web use. A “Best” quality JPEG can be five times larger than a 70% one with no visible difference online. Watch the estimated size in the Export dialog.
• Expecting Preview to convert RAW files perfectly. Preview can open common RAW formats and export them, but photographers who need full control should develop RAWs in Photos or a dedicated editor first.

Conclusion

Preview quietly handles nearly every everyday image conversion: open, File, Export, pick a format. Resize first when files are too big, select every thumbnail when converting a batch, and choose JPEG for photos, PNG for screenshots and graphics, and PDF for documents. With those habits you will never need a random converter website again — or risk uploading your private photos to one.

Frequently Asked Questions

Does converting an image reduce its quality?

Saving as JPEG loses a small amount of quality, controlled by the Quality slider. PNG and TIFF conversions are lossless. Converting from one lossy format to another (HEIC to JPEG) loses a little, but at high quality settings the difference is invisible in normal use.

Why don’t I see formats like BMP or GIF in the Export list?

Preview hides its extended format list. Hold the Option key while clicking the Format dropdown in the Export dialog to reveal every supported format.

Can Preview convert a whole folder of HEIC photos to JPEG?

Yes. Select all the photos, open them in one Preview window, select all thumbnails in the sidebar, then use Export Selected Images and choose JPEG.

How do I make an image file smaller for email?

Export as JPEG and drag the Quality slider down while watching the estimated size, or resize the image first under Tools, then Adjust Size. Either approach can shrink a photo by 90% or more.

Can I convert a PDF into separate images for each page?

Open the PDF in Preview, select a page thumbnail, and Export it as JPEG or PNG, repeating per page. For long documents, dragging thumbnails out and converting the results in a batch is faster.