HD Image Converter changes the picture you already have
Same job as Image to HD: meet a minimum pixel size.
The shorter side is scaled toward 1920 pixels by stretching the existing picture.
What HD Image Converter cannot recover
Do not use this to restore a tiny thumbnail. The result will look soft.
HD Image Converter without the extra promises
HD Image Converter sits on this site because Image and HD are not interchangeable, even when they look similar in a file list. Same job as Image to HD: meet a minimum pixel size. Resize, crop, rotate, compress, or change a photo when the next form has rules. People run an HD tool when a slot asks for a large image and they only have a small one.
The shorter side is scaled toward 1920 pixels by stretching the existing picture.
Read this about Image before you upload
Image tools redraw the picture in your browser. They do not upload the file. These tools do not recover detail the camera never captured. Upscale and HD modes enlarge pixels. They are not AI reconstruction.
Keep the original photo.
Read this about HD before you send the download
The download has to be HD, because that is the format the next step named. People run an HD tool when a slot asks for a large image and they only have a small one. The picture can be scaled so the long side meets a target such as 1920 pixels on image-to-HD tools.
Video-to-HD scales toward 720p height, not a true 1080p master. Read the tool page before you rely on the word HD.
Keep, check, then delete
People lose time when they convert before they know which rule failed. Size, pixel dimensions, codec, font encoding, and layout are different rules. HD Image Converter only addresses the Image to HD step. Same job as Image to HD: meet a minimum pixel size. The shorter side is scaled toward 1920 pixels by stretching the existing picture. Do not use this to restore a tiny thumbnail. The result will look soft. The file stays in your browser and is not uploaded. The limit is 100 MB. Keep the original until the download has been opened in the program that will use it. Do the test with a short or simple file first when the real file is large. A one-page PDF, a single photo, or a one-minute clip will show you whether the output is the kind of file you needed. After that test looks right, run the real file once. Keep both the Image original and the HD download until the receiving person or the upload form accepts it. Photos fail uploads for three separate reasons: the format name, the pixel size, and the kilobyte size. HD Image Converter only does the Image to HD step. If the form also prints a pixel size or a 20 KB or 50 KB cap, do that step with the matching tool, starting from the original each time. A second lossy save will not recover detail.
Here is the decision for HD Image Converter. You start with Image and you stop when a real program accepts HD. The original pixels are what you have to work with. The edit is local. Stretching does not recover detail. A blurry photo becomes a larger blur. If those two sentences describe a tradeoff you do not want, do not convert. Renaming the extension by hand will not do this job. Running the tool twice on its own output will not do it either.
Do not use this to restore a tiny thumbnail. The result will look soft.
A related step, if you still need one, is Image Compressor.
Other jobs start from the homepage, where each tool is named for the conversion it actually does.