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canvas.toBlob() ignores the quality argument for PNG. The HTML Standard applies quality only to formats that support variable quality and explicitly excludes image/png. JPEG and WebP can use a requested quality value, but it does not guarantee a particular file size or identical results across browsers.
Why PNG quality appears to do nothing
The API accepts an optional quality argument, but that does not mean every output format uses it. The WHATWG HTML Standard’s bitmap serialization rule says a user agent applies the value when the requested format supports variable quality and the type is not image/png. PNG is therefore excluded from this quality adjustment.
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If a slider is meant to make PNG files smaller by lowering “quality,” it cannot do that through toBlob(). To affect output size, change the canvas dimensions or content, or offer a lossy format such as JPEG or WebP when supported.
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How PNG, JPEG and WebP handle the quality argument
| Format | Does quality apply? | What to expect |
|---|---|---|
| PNG | No | The standard excludes PNG from variable-quality processing. The quality argument does not control PNG encoder quality. |
| JPEG | Yes, when supported | It is a lossy format; the number requests an encoder quality level, not a guaranteed byte size or universal visual score. |
| WebP | Yes, when supported | MDN documents WebP as a lossy format that can use the quality argument. Confirm the actual output type because unsupported requests fall back to PNG. |
The MDN documentation for toBlob() describes the quality value as an optional number from 0 to 1 and notes that unsupported types fall back to PNG. Values outside that range cause the browser to use its default quality behavior. Even within range, the same number does not promise equal appearance or file size across formats or browser implementations; the standard notes that implementations can interpret “quality” differently.
#1 Best Overall
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Drawing Tablet XPPen StarG640 Digital Graphic Tablet 6x4 Inch Art Tablet with Battery-Free Stylus Pen Tablet for Mac, Windows and Chromebook (Drawing/E-Learning/Remote-Working)
- Battery-Free Pen: StarG640 drawing tablet is the perfect replacement for a traditional mouse! The XPPen advanced Battery-free PN01 stylus does not require charging, allowing for constant uninterrupted Draw and Play, making lines flow quicker and smoother, enhancing overall performance
- Ideal for Online Education: XPPen G640 graphics tablet is designed for digital drawing, painting, sketching, E-signatures, online teaching, remote work, photo editing, it's compatible with Microsoft Office apps like Word, PowerPoint, OneNote, Zoom, Xsplit etc. Works perfect than a mouse, visually present your handwritten notes, signatures precisely
- Compact and Portable: The G640 art tablet is only 2 mm thick, it's as slim as all primary level graphic tablets, allowing you to carry it with you on the go
- Chromebook Supported: XPPen G640 digital drawing tablet is ready to work seamlessly with Chromebook devices now, so you can create information-rich content and collaborate with teachers and classmates on Google Jamboard’s whiteboard; Take notes quickly and conveniently with Google Keep, and effortlessly sketch diagrams with the Google Canvas
- Multipurpose Use: Designed for playing OSU! Game, digital drawing, painting, sketch, sign documents digitally, this writing tablet also compatible with Microsoft Office programs like Word, PowerPoint, OneNote and more. Create mind-maps, draw diagrams or take notes as replacement for mouse
Check what format the browser actually returned
A requested MIME type is not proof of the encoded format. PNG is the required baseline, while other formats may not be supported by a given user agent. If the requested type is unsupported, the browser returns PNG, which can make both a format selector and its quality setting seem ineffective.
canvas.toBlob((blob) => {
if (!blob) throw new Error("Canvas encoding failed");
console.log({ requested: "image/webp", actual: blob.type, bytes: blob.size });
}, "image/webp", 0.8);Read blob.type to verify the result: if it is image/png, the requested WebP format was not honored. The example logs the returned byte count for your own checks; it does not imply a particular expected size.
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HUION Inspiroy H1060P Graphics Drawing Tablet, 10 x 6.25 in, 12+16 Hot Keys | 8192 Pressure Levels, Battery-Free Stylus, Digital Art Tablet Works with Mac, Windows PC and Android
- Working Area Configuration - HUION art tablet equips with a 10 x 6.25 inches working area, providing the user with the most comfortable size to work; the 10mm slim structure and minimalist design of appearance make the drawing tablet more attractive.
- Tilt Function Battery-free Stylus: This computer graphics tablet come with a battery-free stylus PW100, no need to charge, allowing for constant uninterrupted drawing. ±60° tilt support enables imitation of lines input with diverse drawing gestures, with accuracy ensured.
- Press Keys:12 programmable press keys plus 16 programmable soft keys, you can set shortcut keys on drawing tablet's driver based on your preferences, such as erase, zoom in/out, scroll up and down, and so on.
- Compatibility: HUION graphics tablet supports Windows 7 or later/ macOS 10.12 or later/ Android 6.0 or later/ Linux (Ubuntu). A USB adapter is required to connect to a Mac computer. H1060P supports various mainstream design and drawing software, including PS, SAI, AI, CDR, etc. (Please note: The H1060P is compatible with Ubuntu, but it requires the use of the Xorg display server. Wayland is not supported.)
- NOTE: You can easily connect your phone to the art tablet via the OTG connector; while iPhone and iPad are NOT at the moment. The cursor will not show up in the SAMSUNG Galaxy S series at present. If you are not sure whether the product is compatible with your Phone or any help, please contact us.
Designing a useful format and quality control
- For PNG, label the setting as a format choice or adjust dimensions and content; do not present it as a PNG quality control.
- For JPEG or WebP, describe the slider as a requested quality level. Explain that the resulting size and appearance depend on the image and browser encoder.
- After encoding, check the returned Blob type so the interface can distinguish a supported lossy format from PNG fallback.
- Handle a
nullcallback result as an encoding failure rather than assuming a Blob was produced.
Use toBlob() for large image output
For large images, toBlob() avoids building the entire encoded image as a data URL in memory. MDN’s toDataURL() documentation warns that data URLs can cause performance problems and may exceed URL limits, and recommends using toBlob() with an object URL instead.
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XPPen Artist 13.3 Pro V2 Drawing Tablet with Screen, 16K, Full-Laminated | Anti-Glare 123% sRGB Display, 8 Keys for Art, Animation, Mac, PC, Android, Includes Adjustable Stand, Designed for Beginners
- PLEASE NOTE：XPPen Artist13.3 Pro drawing tablet Need to connect with computer,you need to use it with your computer or laptop, the 3 in 1 cable is included
- Drawing Tablet with Screen: Tilt Function- XPPen Artist 13.3 Pro supports up to 60 degrees of tilt function, so now you don't need to adjust the brush direction in the software again and again. Simply tilt to add shading to your creation and enjoy smoother and more natural transitions between lines and strokes
- Graphics Tablets: High Color Gamut- The 13.3 inch fully-laminated FHD Display pairs a superb color accuracy of 88% NTSC (Adobe RGB≧91%，sRGB≧123%) with a 178-degree viewing angle and delivers rich colors, vivid images, and dazzling details in a wider view. Your creative world is now as powerful as it is colorful
- Drawing Pad: One is enough- The sleek Red Dial on the display is expertly designed with creators in mind, its strategic placement allows for natural drawing postures. With just one wheel, you can effortlessly zoom in and out, adjust brush sizes, and flip the canvas—all tailored to suit the habits of everyday artists. The 8 customizable shortcut keys allow you to personalize your setup, streamlining your workflow and enhancing creative efficiency
- Universal Compatibility & Software Support：supports Windows 7 (or later), Mac OS X 10.10 (or later), Chrome OS 88 (or later), and Linux systems. Fully compatible with major creative software including Photoshop, Illustrator, SAI, and Blender 3D. Register your device to access additional programs like ArtRage 5 and openCanvas for expanded creative possibilities.
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GAOMON S620 Graphics Drawing Tablet, 6.5x4, 8192 Pressure & 4 Hot Keys
- 【FOR DIGITAL ART & CREATION】-- Perfect for beginner who starts digital drawing, sketching, graphics design, 3D art work, animation, etc. Also meet basic use of professionals who requires portable feature especially during travel.【FOR ANNOTATING AND SIGNATURE】--You can sign and write in excel, word, pdf, ppt, etc.【FOR ONLINE MEETING & ONLINE CLASS】It works with most online meeting programs, like Zoom, and so on. 【FOR Osu! & GAMING】--It's a large help for playing rythm games like Osu!
- 【PASSIVE PEN】--Battery-free pen cuts the inconveneince of charging the pen. 【8192 HIGH LEVEL PEN PRESSURE & 4 CUSTOMIZABLE EXPRESS KEYS】It will provide you precise control and accuracy at your fingertips, to bring more natural lines and enhance creative performance. 4 customizable express keys could be set to more functions as you like. Using them while working will largely improve your work flow.
- 【COMPATIBILITY OR APPLICATION】-- It compatible with Windows 7 or later and macOS 10.12 or later. Noted: It is not compatible with ipad or iphone. Work with most art programs like Adobe Photoshop, Illustrator, Clip Studio, Lightroom, Sketchbook Pro, Manga Studio, CorelPainter, FireAlpaca, OpenCanvas, Paint Tool Sai2, Krita and so on.
- 【266 PPS REPORT RATE + 5080LPI RESOLUTION + 10MM PEN READING HEIGHT + 6.5*4 INCHES ACTIVE AREA】-- This size is more portable and lightweight, easy to be carried around in the laptop bag to the workplace, school, and travel. But it’s also big enough for digital painting, handwriting, playing games and animation design, etc.
- 【HUMANIZED DESIGN】-- 4 rubber feet are created to ensure the stability of the tablet from slipper. 【LEFT & RIGHT HANDED SUPPORT】--Set 180 degree roate inside GAOMON Driver to set left hand mode.
Rank #3
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XOPPOX Graphics Drawing Tablet, 10×6 Inch Large Active Area with Battery-Free Stylus, 8192 Levels of Pen Pressure and 12 Hot Keys, Compatible with PC/Mac/Android for Painting, Design & Online Teaching
- 【Broad Compatibility】XOPPOX upgraded drawing tablet is compatible with Windows XP/7/8/10/11, Android 4.4 and above, and macOS 11 or later (not compatible with iPhone, iPad, or Chromebook). Note: For Mac users, permissions for Accessibility, Input Monitoring, and Full Disk Access are required in Security & Privacy after installation
- 【No-Battery Pen】The digital drawing tablet comes with a battery-free pen featuring 8192 levels of pressure sensitivity, making lines smoother and more natural. This pen does not need to be charged, so you don’t have to worry about battery power. The package includes 20 replacement nibs
- 【Convenient Shortcut Keys】Designed with 12 customizable shortcut keys and 10 multimedia keys (only compatible with Windows), this drawing pad for pc provides greater convenience and helps improve productivity and efficiency by allowing you to set shortcuts for many different software in the driver settings
- 【Easy to Install】When connecting the graphics tablet to the computer, you can find the installation driver on the removable disk of your computer and install it. Note: After installation, you need to perform some settings and restart your computer before use. If you have any questions about the drawing tablet for pc, please reach out to us directly via "Get Product Support" on the Amazon order page or after-sales email
- 【Wide Range of Use】XOPPOX drawing tablet is compatible with office software such as Microsoft Word, Excel, PowerPoint. It is ideal for online teaching, online classes, remote work, web conferences, presentations, and so on. The art tablet is also compatible with most major software, including Photoshop, SAI, FlipaClip, MediBang, Adobe Illustrator, Lightroom, and more
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
