What Is Image Resizing?
Image resizing changes the pixel dimensions of a raster image — the width and height expressed in pixels. This operation involves resampling: interpolating the color values of existing pixels to generate the color values of new pixels at the target dimensions. The quality of resampling determines how sharp, smooth, or aliased the resized image appears.
Convertly's resize engine uses Lanczos resampling (also called Lanczos3 or sinc resampling), a high-quality windowed sinc interpolation algorithm that is considered the gold standard for raster image scaling. Lanczos resampling uses a 6-pixel kernel (3 lobes) that preserves fine detail and sharp edges during both upscaling and downscaling, avoiding the blurriness of bilinear resampling and the pixelation of nearest-neighbor resampling.
You can resize by exact pixel dimensions (e.g., 1920×1080), by percentage (e.g., 50% of original size), or by one dimension with the other calculated automatically using the locked aspect ratio. All three modes preserve the image format and color profile of the source file.
How to Use Resize Image
- Step 1: Upload Image — Drop your photo or graphic.
- Step 2: Set Dimensions — Input target width, height, or scale percentage.
- Step 3: Download Resized Image — Save your newly sized image.
What to Expect from Image Resizing
What Usually Converts Well
- High-Order Lanczos Downscaling: Downsamples high-resolution photography using Lanczos filtering, preserving fine edge detail without aliased jaggies.
- Aspect Ratio Locking: Proportionally computes the missing dimension when locking aspect ratio, preventing unnatural stretching or squishing.
- Format Continuity: Maintains your source file format (JPEG, PNG, or WebP) with high quality settings upon saving.
- Alpha Channel Preservation: Transparent PNG and WebP graphics retain their transparent backgrounds throughout the resampling process.
What May Require Adjustment
- Upscaling Inherent Softness: Increasing pixel dimensions above native resolution cannot add real optical camera detail; enlarged pixels appear softer.
- Proportions if Aspect Ratio Is Unlocked: Specifying arbitrary width and height without keeping ratio will distort natural object proportions.
When to Inspect Output
- Substantially Enlarged Graphics: Inspect sharpness when upscaling small graphics to larger dimensions.
- Custom Non-Proportional Dimensions: Verify that unlocked aspect ratios did not produce undesirable stretching across subjects.
Before You Resize: Technical Boundaries & Limitations
Cannot Synthesize Sensor Resolution
Upscaling increases pixel count via interpolation filters; it cannot generate real optical information absent from the original.
Aspect Ratio Distortion When Unlocked
Entering non-proportional width and height values without ratio locking stretches the pixel grid.
100 MB File Size Ceiling
Images up to 100MB are supported per session.
Troubleshooting Common Resize Image Issues
Q: My resized image looks blurry or soft compared to the original.
Blurriness occurs when upscaling (making an image larger than its source resolution). Lanczos produces the sharpest possible result, but no resampling algorithm can recover detail that does not exist in the source pixels. Always resize from the highest-resolution original available.
Q: The aspect ratio lock is producing unexpected dimensions.
With aspect ratio lock enabled, entering one dimension automatically calculates the other proportionally. If the output dimensions must exactly match both values, disable aspect ratio lock and enter both dimensions independently — this will stretch the image non-proportionally if the aspect ratios differ.
Q: My transparent PNG image has a white background after resizing.
Convertly preserves alpha channel transparency in PNG output during resize operations. If you are seeing a white background, ensure you selected PNG as the output format — JPEG does not support transparency and will composite alpha to white.
Frequently Asked Questions (Resize Image)
Will my image get stretched or distorted?
No, aspect ratio locking prevents distortion unless you explicitly override it.
Is Convertly’s Resize Image tool completely free to use?
Yes. Convertly’s Resize Image tool is 100% free with no hidden subscription fees, no trial limits, and no daily conversion caps. You can process files whenever you need without credit card details.
How long are my uploaded files stored on your servers?
Under our privacy policy, all uploaded files and converted outputs are stored in temporary server storage and are automatically deleted after 120 minutes.
Will my file formatting, fonts, or image quality be lost?
Convertly uses standard processing engines (including PyMuPDF, LibreOffice, and Pillow) to preserve document layout, vector geometry, font styling, and image fidelity where supported by the respective target formats.
Do I need to create an account or register to use Resize Image?
No account registration is required. We do not ask for your email address, phone number, or personal details. Simply upload your file, execute the task, and download your result instantly.
Can I use Resize Image on my iPhone, iPad, or Android phone?
Yes! Convertly is fully mobile-optimized. You can access the tool on any smartphone or tablet, select files directly from device storage or cloud drives, and even scan a QR code to transfer files to your phone.
Does this tool work on Mac, Windows, and Linux?
Yes. Convertly runs entirely in your web browser and is fully compatible with Windows 10/11, macOS (Intel & Apple Silicon), Linux (Ubuntu, Fedora, Debian), and ChromeOS across all modern browsers.
What is the maximum file size limit for uploads?
You can process files up to 100MB per session, which provides ample headroom for heavy multi-page documents, high-resolution photographs, and complex presentations.
Does Convertly add watermarks to my converted files?
No. We never stamp logos, watermarks, branding labels, or promotional text onto your documents. Your output files remain clean and professional.
Which web browsers are supported?
Convertly supports all modern web browsers including Google Chrome, Apple Safari, Mozilla Firefox, Microsoft Edge, Brave, and Opera without needing third-party plugins or browser extensions.
Can I convert multiple images at the same time?
Yes! Convertly supports multi-file batch uploads so you can process multiple graphics sequentially with high-speed parallel workers.
Are my files used to train AI models or shared with third parties?
Never. Convertly maintains a strict Zero AI Model Training policy. Your documents and images are never read, analyzed, shared, sold, or used to train machine learning models.
Can I continue editing my document with other Convertly tools?
Yes! You can seamlessly pipe your result into our other 29 conversion tools, such as Compress PDF, Merge PDF, Protect PDF, or Convert to Word.