What HD means in pixels and aspect ratios
HD is a display standard, not a vague promise of quality. 720p, usually just called HD, is 1280×720 pixels, a little under one megapixel. 1080p, or Full HD, is 1920×1080, about two megapixels. Both are 16:9 frames, the shape of most TVs, laptop screens and video players.
Photos rarely start in that shape: phones usually shoot 4:3 and many cameras 3:2, so even a large picture can show black bars on a widescreen display. Turning a photo to HD therefore has two parts, enough pixels and the right shape. If you crop a landscape photo to fill a 16:9 screen, its width has to reach 1280 or 1920 pixels. If you show it uncropped with bars at the sides, its height has to reach 720 or 1080, and a portrait photo on a TV is always that case.
Which starting sizes reach HD at 2x and at 4x
Upscaling multiplies both sides: 2x doubles width and height (four times the pixels), and 4x quadruples them (sixteen times the pixels). A 640×360 image at 2x becomes 1280×720, exactly 720p, and at 4x becomes 2560×1440, more than Full HD. A 960×540 image at 2x lands on 1920×1080, exactly Full HD.
Working backwards, 2x reaches 720p from a 16:9 image of 640×360 and 1080p from 960×540. At 4x the minimums fall to 320×180 and 480×270, but sources that small hold so little information that much of the result is the model's best guess. When 4x overshoots, scale the output down to your target in any image editor.
One rule applies to large uploads: in every mode except Anime, images above about 6 megapixels (2.25 for 4x) are first scaled down in your browser, and the output is 2x or 4x of that. For HD this rarely matters, since a 2x result can reach about 24 MP, more than ten times Full HD.
Photo to HD for old phone pictures and chat downloads
Early camera phones saved pictures at 640×480, the VGA size, and many of those files still sit in old backups. At 2x a VGA picture becomes 1280×960, which covers a 720p frame once cropped to 16:9; at 4x it becomes 2560×1920, enough for a Full HD crop. Those small sensors also produced grainy, soft images, and the model reduces grain and softness to a degree as it enlarges.
Images saved from chat apps are a different problem. Messaging services commonly shrink and recompress photos, so the saved copy may be small and marked by blocky JPEG artifacts, which the upscaler reduces to a degree along with noise. Before you start, ask whether the full-size original still exists on the sender's phone or in a cloud backup: a real original always beats an upscaled copy of a compressed one.
Target sizes for thumbnails, slides, banners, frames and TVs
Video thumbnails are commonly made at 1280×720, so 720p is the target there. Most presentation apps default to 16:9 slides, and a photo filling a whole slide on a 1080p projector or TV needs 1920×1080 to stay crisp; one filling half the slide width needs about half as many pixels across. Social platforms resize uploads to their own dimensions, so an HD version gets scaled down rather than stretched up, which generally looks cleaner.
Website banners are wide and shallow, so width counts. A banner across a desktop browser window is often displayed around 1920 pixels wide, and a narrower source gets stretched by the browser and looks soft beside crisp text.
Digital photo frames and TVs are where small old pictures look worst. A 640×480 photo shown full height on a 1080p TV is stretched 2.25 times by the TV's own scaling, which softens everything; doing the photo to HD step here first leaves the screen little stretching to do. For a frame, look up its screen resolution and upscale until the photo at least matches the screen height.
When a picture is too small or too blurry for HD
Not every photo to HD conversion is worth doing. A 160×120 thumbnail becomes only 640×480 even at 4x, still short of 720p. A photo blurred by bad focus or movement gets firmer edges, but detail the camera never captured does not come back, and a big screen makes the remaining softness more obvious.
Heavy compression behaves the same way: the upscaler reduces JPEG blocks to a degree, yet an image saved and resent many times can come out smooth and waxy in skin, grass and sky. In a distant group shot, a face only a handful of pixels wide stays a soft impression at 1080p.
The practical check is the before/after slider. Look at eyes, hair, lettering and straight lines; if they hold up, use the result at full size. If they look painted, aim lower, such as 720p instead of 1080p, or show the photo smaller on the slide or page.
Getting the best photo to HD result: source, mode and scale
Start from the best file you have: the original from the camera roll or a backup, not a screenshot or a copy forwarded through a chat, because every resave removes information the model could have used. Uploads can be JPG, PNG or WebP up to 25 MB, and results usually arrive in 5 to 15 seconds, ready to compare on a before/after slider and download.
Photo mode, preselected on this page, suits camera pictures. It runs the same Real-ESRGAN model as the Basic and Screenshot presets, so switching among those three does not change the engine. Anime mode uses a separate Real-ESRGAN build meant for flat colors and line art, and suits drawings rather than photographs.
For scale, choose the smallest setting that reaches your target. A 2x job uses 1 credit and a 4x job uses 2, so 2x is also the cheaper choice whenever it lands on or past 1280×720 or 1920×1080.