Batch · Rec. 601 luma
Bulk Grayscale Converter
Convert a whole set of images to black and white with a single, predictable formula — and keep the transparency if you output PNG.
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Bis zu 50 Dateien und 200 MB pro Stapel
Verarbeitung im Browser — nichts wird hochgeladen.
Stapel-Einstellungen
PNG behält den Alphakanal. JPG legt Transparenz auf Weiß.
Downloads kommen direkt aus dem Arbeitsspeicher des Browsers. Es wird nichts gespeichert.
Turning a picture grey is not one operation but several, and the difference shows on skin, sky and anything red. This tool uses Rec. 601 luma: each pixel becomes 0.299 times its red, plus 0.587 times its green, plus 0.114 times its blue. Those weights approximate how human vision responds, which is why a red jumper stays visibly darker than a green one instead of collapsing to the same grey the way a naive average would render them. The alpha channel is copied through untouched, so a transparent PNG logo comes out grey with its transparency intact.
80 press photos that have to print in one ink
A community newspaper prints in black only. The photo editor receives 80 colour JPEGs each week and needs to see, before layout, which ones survive the loss of colour — a red-jacketed runner against green grass is striking in colour and almost invisible in grey, because those two colours land within a few points of each other on the luma scale. Running the whole set through in one pass takes under a minute and makes the weak frames obvious immediately, without touching the colour originals, which stay on disk for the website.
How bulk grayscale converter works
Add the images
Up to 50 files, in any of the formats the browser can decode.
Pick the output format
PNG keeps transparency and stays lossless. JPG produces smaller files and flattens any transparency onto white.
Convert
Each file is decoded, run through the same pixel kernel the single-image grayscale tool uses, and re-encoded.
Download
Individual files or the whole batch as one ZIP.
Limits, stated plainly
- 50 files and 200 MB per batch.
- One fixed formula: Rec. 601 luma at 0.299 red, 0.587 green, 0.114 blue. There is no strength slider, and there is no channel mixer.
- Transparency survives only in PNG output. Choosing JPG flattens transparent areas onto white before converting.
- Very large images are held in memory as full-size pixel arrays while they are processed, so a batch of 40-megapixel files will be slower and heavier than a batch of web-sized ones.
- Metadata is not preserved through the re-encode.
Every file in this batch is decoded, processed and re-encoded inside your browser tab. No image data is sent to a server, there is no queue, and there is no account. The ceilings above (50 files, 200 MB) exist because your device holds every decoded image in memory while it works.
What this tool will not do
- It will not produce a sepia or duotone look. Those are separate tools with their own colour handling.
- It will not let you weight the channels yourself, the way a darkroom red filter would. This is one fixed, predictable conversion.
- It will not adjust contrast afterwards. Grey images often want a contrast lift; that is a different tool and a deliberate second step.
Bulk Grayscale Converter — questions people actually ask
Why not just average the red, green and blue values?
Because the eye is far more sensitive to green than to blue. A plain average renders pure red and pure green as the same mid grey, which is wrong for almost every photograph. The Rec. 601 weights used here keep the relative brightness people actually perceive.
Does my transparent PNG stay transparent?
Yes, if you keep PNG as the output format. The conversion touches only the red, green and blue channels; alpha is copied through byte for byte. Selecting JPG will flatten those areas onto white, because JPEG has no alpha channel.
Is this the same as desaturating in a photo editor?
It is the same family of operation but not always the same numbers. Editors offer several conversions — luminosity, average, lightness, channel mixer — and they produce visibly different greys. This tool always uses Rec. 601 luma, so every file in every batch is treated identically.
Can I get the colour back afterwards?
Not from the grey file. Converting to grayscale discards the colour information permanently, which is why the tool writes new files and never overwrites your originals. Keep the colour versions.
Why is my black-and-white JPEG barely smaller than the colour one?
JPEG already stores colour at reduced resolution and spends most of its bytes on brightness detail. Removing colour therefore saves less than people expect — usually 10 to 20 per cent. If size is the goal, lower the quality or use the bulk compressor.
Other batch tools
Bulk Image Compressor
Shrink a whole folder of photos in one go, with the real before-and-after size on every row. The encoder runs in your tab, so nothing is uploaded.
OpenBulk Image Resizer
Drop a folder of photos, set one rule, and every file comes back at the new size. Nothing is uploaded — the resizing happens on your own machine.
OpenBulk Image Converter
Point a mixed folder at one target format. PNG, JPG, WebP, GIF, BMP and iPhone HEIC files all go in; PNG, JPG or WebP comes out.
Open